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Twincharging with Screw-Type SC instead of Roots

Twincharging with Screw-Type SC instead of Roots

Twincharging with Screw-Type SC instead of Roots

(OP)
Twincharging an engine that features a screw-type supercharger (ie it already has internal compression) in my mind has the following advantages and disadvantages:

Disadvantages:
It would still feature parasitic loss when the supercharger is "bypassed" and the turbo is powering away at higher rpm

Advantage:
The efficiency being better than a roots blower, would mean lower temps and more power

Can one of the gurus post their thoughts? PatPrimmer and Warpspeed had a lot to say on previous TwinCharge topics.

In short: what is the suitability of screw-type SC for twincharging project?

PS: I really have the twincharge bug! help!
 

RE: Twincharging with Screw-Type SC instead of Roots

You've probably got it ... the screw type would give (theoretically) an efficiency loss during cruise, but a minor power improvement during the short period of acceleration until the turbo takes over.

The twin-charging application that I'm aware of (VW) only uses the supercharging for the first moment of acceleration in which the turbo is running "off design". As soon as the engine builds enough revs for the turbo to take over, it does. This leads me to suspect that there is little purpose in using a higher efficiency supercharger, because it is really only used for maybe a second at a time. Also, those engines are intercooled, so whatever minor extra heat comes from using a supercharger that is less efficient than it could be, gets taken away by the intercooler anyway.

At least in that application, the need to minimize parasitic losses during cruise and acceleration when the turbo is active takes priority.

'course, not every application is the same, I'm speaking only of that one, where VW's intention was to make a downsized and more-efficient gasoline engine; it's best not to throw away a few points of efficiency driving an inactive supercharger.

RE: Twincharging with Screw-Type SC instead of Roots

Also, I'm thinking the lower heat capacity of the oil would make for more of a temperature differential when it hits the radiator, improving cooling of the oil there. Would help any bit? Also, engine oil could go higher in temp with no risk of it boiling, even in an unpressurized system.

Anyone done this or know of this having been done?

RE: Twincharging with Screw-Type SC instead of Roots

Have you considered electric clutching the supercharger?  Mercedes, on the original SLK230 had an electric clutch on their 2.3l four cylinder, Eaton M45 supercharged, which in my mind could potentially open many options for a twin charged application.  Mazda, with the twin turbo RX7 of 1993 through 1995, had a very complex system of making the turbos sequential.  I'm not saying it was especially good, but when in a good state of tune, that system gave a nice flat torque curve, coming on low, which the little rotary really needed.  If designed properly, twin charging should be able to eliminate the parasitic loss of the supercharger, when no longer needed, or overtaken by the turbocharger.

j79 guy

RE: Twincharging with Screw-Type SC instead of Roots

This has all been done before. At this stage I have nothing further to add other than a small Roots at low boost vs a small screw at low boost does not impact all that much on total efficiency compared to the alterntive ways to get the same power and response.

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

(OP)
Thanks for the responses guys, the question is redundant now. I was contemplating buying the mazda Miller cycle engine 2.3L that comes with a lysholm type supercharger, then just adding the turbo - hence the question about whether or not it'll be a problem using the lysholm!

I'm now leaning towards the subaru EJ20T as used in the STi as a candidate. By choosing an engine that's already fed force induction, then compression etc is already sorted.

I was also looking at the SR20DET.

In my location, there are displacement rules that coincide with vehicle weight. It works out that a 2L turbocharged engine can be put in a 800kg car, provided the engine will meet the emissions requirements of the car. So if I choose a mazda mx-5 (miata) between '89 and '97 then it weighs 940kg and all should be good. Although I'm not sure if the boxer will fit between the miata chassis rails...

RE: Twincharging with Screw-Type SC instead of Roots

jbond:  As you know, the EJ20T has terrible turbo lag.  Once on the boost, they are stellar, but waiting for the turbo to spool can be irritating.  An Eaton 45 supercharger, or equivalent would snap up the throttle response quite nicely.  However, I doubt you will find a satisfactory fitment to the MX5 chassis.  I've contemplated this swap as well, and was leaning to the Oldmobile Quad-4, mid 1990's vintage.  The new Ecotech 2.0 engine, which is an evolutionary growth of the Quad-4, would potentially be even better.  The new Ecotech turbo engines will start showing up in the wreckers shortly.

j79 guy.

RE: Twincharging with Screw-Type SC instead of Roots

(OP)
j79 guy, thanks for the tip. I'll look into the Ecotech turbo engines too.

I quite like the novelty of the boxer, the look, the sound, etc :) Plus I think they're already designed for around 18psi and 8k rpm which is plenty in a sub 1000kg car

RE: Twincharging with Screw-Type SC instead of Roots

The Subaru engine looks just right for an upside down Eaton supercharger, and it would not interfere with factory style turbo location whatsoever.  It looks like it would complement it, actually.  (As such, I am acquiring the bits and pieces to take on this project!)

I realize VW does things their way, but I thought the main advantage to twincharging involved the pressure differential/heat characteristics when you ran the turbo and supercharger in series rather than in parallel sequence.  Bypassing the blower would seem to revert it to a standard, if not now highly complex, turbo engine.

 

RE: Twincharging with Screw-Type SC instead of Roots

In series keeps a system that i complex by definition as simple as possible, or is that as least extremely complex as possible.

Regards

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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Twincharging with Screw-Type SC instead of Roots

(OP)
izzmus, yes great idea, to upside-down mount the eaton below the intake manifold. Is there enough clearance room there?
Additionally, I had always hoped of fitting an A/W intercooler after the eaton, that would take at least an additional inch of space for a highly compact solution. Perhaps spacers where the intake manifolds meet the heads (if they meet orthogonally)

twincharged AWD sounds like the ducks nuts as you wouldn't be spinning the wheels like rwd may do if you have too much torque off idle

RE: Twincharging with Screw-Type SC instead of Roots

A custom intake manifold is assumed.  Fortunately, Subaru saw fit to make the turbo engines (for the North American market at least) with three piece intake manifolds, with the fuel injectors and rails attaching to the lower stubs.  A custom intake manifold is not therefore going to be nearly as time consuming to fabricate as it could be.

Believe it or not, my plans are for front drive.  As it will be entirely on an experimental, beer-money type basis, I don't want to have to deal with the reputation for drivetrain breakage that Subarus have earned.  Not yet, at least.
 

RE: Twincharging with Screw-Type SC instead of Roots

(OP)
FWD in what body? An imprezza or liberty, or something entirely different?

Here's some pics:






Alternator, Power Steering Pump, AirCon Compressor - which one are you going to remove? Or, will you accomodate them with a bracket to re-mount it a little to the side? :)




 

RE: Twincharging with Screw-Type SC instead of Roots

This is getting off-topic, so this will be my last post on the subject (a valid e-mail address will not be hard to find if you wish to go off-board) but the models here are a tad different, and all one needs to do is look into "reversed intake manifolds" (positions throttle to face forward) to see the options for relocating accessories.

Trying to steer back on topic, the screw type superchargers require less power for a given boost level, so the drop in parasitic loss alone would be advantageous.   

RE: Twincharging with Screw-Type SC instead of Roots

The twincharged VW engine has an electromagnetic clutch that completely disengages the supercharger when it's not needed, so the associated parasitic losses of the bypassed supercharger is not there.  In fact, I don't know of any contemporary OEM supercharged application that doesn't have a clutched disengagement during part load.

Care should be taken about discussing efficiencies.  While it is well known that screw compressors have internal compression, the general blanket conclusion is that this is more efficient than a positive displacement blower.  This is true at increasing pressure ratios, but in fact, at low PRs the difference approaches insignificance, and a Roots blower can get better efficiencies than a screw compressor because of less aggregate losses (the work of a compressor covers more than simply the process work).

Generally, if the PRs of the compressor stage is less than about 1.5, the differences in efficiencies are pretty small, and cost becomes the overriding factor.  However, the VW TSI engine has the blower delivering a PR of 2.5 barely above idle at 1250 RPM, and IMO a screw compressor would be better suited for this, but again, cost was the overriding factor.

In an SI engine, a large reduction in compressor work and charge temperatures can be achieved by injecting fuel at the compressor inlet, as Lotus has done with the Exige 265E and 270 Tri-fuel prototypes.

RE: Twincharging with Screw-Type SC instead of Roots

After re-reading a paper I have on the TSI, I must amend my comment on the supercharger PR.  At 1250 RPM full-load, the total PR is 2.5, but the contribution of the supercharger itself never exceeds a PR of about 1.75.  At this operating point, the total PR is achieved by a series connection of the supercharger and turbocharger, the respective PRs being 1.75 and 1.43.  The supercharger PR is on a downward slope, and the turbo PR is going upward, until the turbocharger takes over completely beyond about 2500 RPM to redline, again at full-load.

RE: Twincharging with Screw-Type SC instead of Roots

Quote:

Although I'm not sure if the boxer will fit between the miata chassis rails...  
its a bit off topic but you can make anything fit :)
I once saw a crosly wagon with a 426 hemi.

http://classiccars.com/Uploads/Preview/34926.jpg

Luck is a difficult thing to verify and therefore should be tested often. - Me

RE: Twincharging with Screw-Type SC instead of Roots

The Thing Is I Have Both A Mercedes Supercharger (Screw Type) Off A C180K And A Mitsubishi Turbo. It Was Not My Intention To Use Both On The Same Car (1700cc Motor)

But The Supercharger Does Not Have An Electro-Magnetic Clutch Which Would Be Ideal. Short Of Designing One Or Adapting Another I Need A Plan.

Plus How Would One Design The Plumbing. Would Both The Chargers Meet At The Intercooler.

If It's A Ball-Ache I Rather Not Have The Labour Pains :)

Has Anybody Done Something Like This Before?

RE: Twincharging with Screw-Type SC instead of Roots

The plumbing layout is easy.

Air into turbo via filter and bell mouth.

From turbo to intercooler if  available.

From inter cooler to throttle body.

From throttle body to the belt driven supercharger inlet.

From the belt driven supercharger to the intercooler if available.

The use of intercoolers and where thy are is optional but desirable. One should suffice unless you are generating a lot of boost at both stages.

Typically best results are obtained with moderate boost at the belt driven but a lot of boost from the turbo, so the critical intercooling area is after the turbo, but this can either be directly after or the belt driven. I think there is a slight advantage to feed cool air into the belt driven, but there is also some intercooler efficiency gain by feeding hot air into the intercooler, but I am guessing re this aspect. One intercooler after the belt driven is the simplest and most thermally efficient so long as the belt driven can run efficiently and durably at the inlet air temperatures it would get directly from the turbo outlet.

 

Regards

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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Twincharging with Screw-Type SC instead of Roots

Yes That Is A Method That Could Work.

There Are Three Ways To Go About This I Suppose.

Turbo Before (Feeding) Super
Parallel
Super Before (Feeding) Turbo

I Was Thinking More Along The Lines Of Going Parallel With The Super Working Until Say 2000Rpm Then Disengaging The Clutch Of The Super By Then The Turbo Should Have Overcome It's Lag Stage.

But The Super Doesn't Have A Clutch.

Also Doesn't Feeding A Turbo Or SuperCharger With Compressed Air Further Increases It's Compression? Just A Thought. Sort Of A Compound Turbo-Charging Situation. If So I Would Have To Decrease My Compression Ratio To A 5.8 :1

This Is Exactly Why People Don't Often Do This. The Road Less Travelled.

RE: Twincharging with Screw-Type SC instead of Roots

What's with the capital letter at the beginning of each word??

Anyway, the trouble with doing any sort of change-over is that it's potentially abrupt and can cause driveability problems.

The VW arrangement has the supercharger in front and the turbocharger second. The turbo "sucks" through the supercharger. When the turbo is "sucking" enough to draw the supercharger outlet below atmospheric, it bypasses the supercharger (and in that case de-clutches it, but a simple flapper that acts like a check valve will do the job as well, just won't reduce the mechanical losses). This arrangement gives a near-constant pressure ratio and even when the turbo isn't quite "on boost" yet, whatever boost it does create is unloading the supercharger to cut down power demand to drive it.

A parallel arrangement would have a significant risk of running the compressor in surge (too little flow through it) when the engine is in supercharger mode, and it would not make use of the turbo to unload the supercharger.

RE: Twincharging with Screw-Type SC instead of Roots

Sucking through a positive displacement pump does not work, other than to reduce effort to drive the pump.

To draw in extra air for the turbo you need a bypass. The bypass is an extra complication that you don't need if you run the turbo directly into thebelt driven blower.

Yes if you make more boost you need less compression or higher octane fuel, NO MATTER HOW YOU GET THE BOOST.

Have you read the previous treads on this as you seem to be missing some basic points that were covered previously.

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

Before stating that it doesn't work, might want to take a closer look at how VW did it, because that's the way theirs is, and it's in production.

The VW twin-charged engine is not designed to make the absolute maximum possible amount of power. It is designed to have a flat torque curve and to be as efficient as a gasoline engine can be (by downsizing it). The supercharger is only used when the turbo is "off-design" (takeoff from a standstill). The turbo is designed to unload the supercharger as quickly as possible, as soon as the revs come up.

RE: Twincharging with Screw-Type SC instead of Roots

As I understand it VW has a bypass. I said it does not work to such through a positive displacement pump. With a bypass, it does not try to suck through the positive displacement pump.

I stand by my comment.

With the resources of an OEM you might be able to tune the bypass to switch over the boost source smoothly, however a a hot rodder that might be more complicated, which I why I advise the less complex method.

Al;so hot rodders typically are looking for more power, not more economy. I doubt that no matter how the OP does this that he will improve his fuel economy, but he will immprove power.  

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

I Have Read The Thread Again And Yes I Did Miss Plenty Good Points. Sorry About The Caps It's Habit More Than Anything.

I Must Admit Im Still A Junior To The Whole Supercharging Idea, I Know Plenty About The Turbocharger But Using Them Together Is New Grounds.

My Only Worry About Running The Chargers In Series Was The Extreme Increase Of Compression. And In That Lies The Reason Why I Opted For Parallel Charging.

I Didn't Say That Series Charging Was Impossible, I Just Didn't Read The Thread Properly.

The SuperCharger That I Have Is An Eaton Type And Not A Screw-Type As I Mentioned. Sorry

I Think That Having The Super Feeding The Turbo Is Rather Complicated In That A Bypass Valve Is Required, And Once Again Im Not Too Sure Of The Plumbing.
But The Turbo Feeding The Super Is A Better Idea, The Only Drawback Is The Two Intercoolers, I Would Rather Have Two Mainly To Prolong The Life Of The Super.

But Once Again Could Someone Advise If The Compression Would Change From One To The Charger To The Other. Thus Dramatically Reducing The Compression Ratio Of The Engine.

I Really Appreciate You Guys Bearing With Me And My Q's As I Come Up To Speed With Things.

RE: Twincharging with Screw-Type SC instead of Roots

Re he typos in my last post. Sorry I posted late at night and saw some serious misquotes of my previous statements and reacted to correct them when I should have been sleeping.

Once again. The compression is dependant on the maximum total boost and charge temperature. The combustion chamber has no idea how you get to that.

For instance, if the roots blower produces 15 psi at a certain rpm and charge temperature, it tolerates the same compression as a turbo producing the same.

If the roots blower produces 7.5 psi or a multiplication factor of 1.5 times atmosphere, and the turbo feeds it at 15 psi then you get 22.5 psi boost. You need the same compression as if you get 22.5 psi boost any other way

 

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

Thanx Pat For Answering My Q's

If I Were To Add The SuperCharger First Run With It And See Where The Power Comes In And Out (And After That Add The Turbo)

My Q Is Do I Need To Add A Dumpvalve To The SuperCharger Plumbing, I Don't Think So Cause The Supercharger Is Belt Driven.

Then If I Had Both The Super And Turbo I Would Still Need The Dumpvalve. I Know It's A Stupid Q But I'd Rather Make Sure.

Pat You Said

"The plumbing layout is easy.

Air into turbo via filter and bell mouth.

From turbo to intercooler if  available.

From inter cooler to throttle body.

From throttle body to the belt driven supercharger inlet.

From the belt driven supercharger to the intercooler if available."

Does The Throttle Body Have To Be Before The SuperCharger And Not On The Inlet Plenum?
 

RE: Twincharging with Screw-Type SC instead of Roots

Yes

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

Why

RE: Twincharging with Screw-Type SC instead of Roots

Because, like I said in PREVIOUS THREADS, a Roots blower is positive displacement, and if fully throttled downstream, pressure builds up and bends or breaks things, like the throttle plates, then you have a damaged throttle that can't be closed, then you have  runaway engine.

I am really fed up with doing your homework for you. READ THE PREVIOUS THREADS if you expect any more help from me.  

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

Yes it does get extremely tedious Pat, I too am sick and tired of people asking the same very basic questions that have already been answered many times over and over, and then wanting to start an argument over it.

To put it simply, the best and simplest way to do this is to place the turbo compressor ahead of the positive displacement supercharger (in series), and use a load sensitive air bypass system directly around both the supercharger and turbo compressor, that opens at idle and small throttle openings. Leave the throttle body right where it is on the plenum, down stream of the supercharger for the fewest drivability problems.

To respond to the original poster, It depends on which is most important to you, full throttle performance, or part throttle fuel economy. A roots blower is well up to the job and has the lowest parasitic losses when fully bypassed. A screw blower will consume some power, even when fully bypassed, as the supercharger heat and noise will quickly tell you.  

At the generally low supercharger boost pressures required for twin charging, the screw blower hardly seems worthwhile, unless you already have one on the engine all set up ready to go.

RE: Twincharging with Screw-Type SC instead of Roots

That one most definitely is Roots blower and then turbo, with a flapper / check valve to allow the turbo to draw in air bypassing the Roots blower when it feels like drawing in more air than the Roots blower is supplying.

The VW arrangement is similar in concept.

These OEM applications are using the Roots blower to fill in the bottom end of the torque curve before the turbo "spools up", and use the turbo to unload the roots blower as it picks up speed.

RE: Twincharging with Screw-Type SC instead of Roots

(OP)
Don't get confused with "what's best for OEM is what's best for you"

you may have a different set of priorities

it is common sense to understand and to acknowledge that OEM are in the business of making a profit ($)

when people buy a performance car or a performance motorbike, one of the first things they do is replace the exhaust system and the intake filters because of the recognised compromises that are made in the manufacture of them

OEM's calculate what is the cheapest implementation of something that will suffice and yet yield the greatest profits, and then that is the business case

forget VW, look how complicated their implementation is, there are guys on this forum that have implemented the turbo followed by roots and even posted videos of it on youtube and it rocks...

RE: Twincharging with Screw-Type SC instead of Roots

It certainly looks that way, the pipework is extremely confusing follow just from those pictures.

But just remember, that is a marine diesel engine.  There is no throttle butterfly to suddenly block off airflow. No wastegate either.

Accelerating up through a manual gearbox in a road car involves some fairly drastic throttle butterfly movement, and that places far more stringent requirements on throttle response than a marine or aircraft engine.

While that pipe layout obviously works just fine in a boat, It would create some HUGE drivability problems if copied in a gasoline powered a road car.

For instance, where would you insert the throttle butterfly? And those total pipe volumes look enormous. All perfectly fine for the application, but completely unsuitable for an air throttled gasoline road application.

RE: Twincharging with Screw-Type SC instead of Roots

VW's gasoline (TSI) implementation has the throttle body before the intake manifold (after the turbo and intercooler etc), same as every other turbo gasoline engine.

Regarding throttle closure, I am rather sure that VW's system will use the same style of internal bypass valve around the turbo compressor that they do on their other production turbo engines (2.0T, 1.8T). On that engine, the supercharger is clutched, and the computer is programmed for the conditions on when to engage or disengage this clutch (and the flapper that bypasses the supercharger).

No question that aftermarket may have different priorities than OEM. No question that cost is an issue for an OEM (but what's the difference in cost whether the turbo or super comes first? I can't see it). No question that there are multiple ways to accomplish this. The fact that this thread has so many responses and discussion is evidence of that on its own.

It's equally important to understand why the OEM's do it the way they do it, and what the advantages and disadvantages of each arrangement are, and what all the issues are that need some sort of work-around or some extra control devices, and how those controls should work.

So far, we've discussed two OEM implementations, one gasoline and one diesel, both of which are supercharger first (on the low pressure side), turbo second, with some means (flapper valve and/or clutch) of bypassing the supercharger when it is not needed.

RE: Twincharging with Screw-Type SC instead of Roots

The OEMs have one big advantage over the do it yourself Hot Rodder, in that they can use the existing electronic engine management system to control any air bypass system or clutch.

So for them, the control system costs almost nothing (once fully developed) because most of it is already there.

Any air bypass around the supercharger absolutely must be smooth, linear, and extremely progressive in action. The infamous noisy and abrupt turbo blowoff valves are totally unsuitable  for this application.

As you slowly open the throttle from light load, to something slightly more, you certainly don't want valves or flaps suddenly flying open or slamming shut, and massive sudden changes in engine induction air pressure. Clutching and de-clutching the blower smoothly is not as simple as it  looks either.

If you suddenly slam your foot on the throttle, how do you start up a completely stationary blower without creating a massive mechanical and pressure shock load ?

Instead of a clutch, use a turbo external wastegate (fitted with a light spring) as a supercharger air bypass, actuated by the pressure differential across the throttle body. Use this to completely unload, and SMOOTHLY load up the blower, but keep the blower rotors turning always.

My advice to anyone planning to build a twincharge system with EFI would be to leave the throttle body in the original factory position if at all possible.

Where you fit the turbo into this is entirely up to you. But placing it ahead of the supercharger requires no additional controls on the induction side.

If you place it after the supercharger, some type of air diverting flap will be required. That will almost certainly introduce a whole series of extra problems you could well do without for gasoline road application.

One of the less obvious advantage of placing the turbo compressor ahead of the supercharger, is you will never have any problems with compressor surge, or compressor stall. The supercharger is always drawing significant air volume through the turbo compressor, even with a fully closed throttle. It has been proven to work extremely well countless times, and is simple.  Why complicate things unnecessarily ?

RE: Twincharging with Screw-Type SC instead of Roots

Warpspeed:  Just remember that Volvo-Penta marine engines have air-to-water and water-to-water heat exchangers, not the air-to-air and water-to-air exchangers that this engine has.

PJGD

RE: Twincharging with Screw-Type SC instead of Roots

The latter point is only true if the air being drawn through the supercharger is being spilled / vented to atmosphere. Normally on supercharged applications, the throttle is in front of the supercharger, which means that latter point won't be any more true than with a naturally aspirated engine. (Closed throttle = next to no airflow, supercharged or not. Same situation for the turbo.) "Unmeasured air" on an EFI system that uses a MAF (mass airflow) sensor will cause trouble.

This stuff ain't simple, no matter which way it's done.

RE: Twincharging with Screw-Type SC instead of Roots

That is the whole point Brian.

With a positive displacement supercharger, and the throttle placed down stream, air MUST be recirculated to unload the supercharger at very small throttle openings. And to prevent destructive boost spikes on sudden high rpm throttle closure.

The closer the throttle(s) are to the intake valves, the crisper the throttle response will be. The really serious normally aspirated guys are well aware of this, but the forced induction people often choose to ignore this simple truth.

If you plan to run a seriously large intercooler after the supercharger, (and you should), placing the throttle over the supercharger intake is a very backward step. How bad it ends up, depends on what you have. But it will definitely feel distinctly worse to drive.

 

RE: Twincharging with Screw-Type SC instead of Roots

If one was to intercool the air after the turbo before entering the supercharger would a liquid charger cooler after the supercharger suffice.  

RE: Twincharging with Screw-Type SC instead of Roots

What Warpspeed says about response is true, but if you close a throttle after a positive displacement blower, you need a pressure relief valve in the manifold between the blower and the throttle. If this valve sticks closed, pressure will build up against the throttle plates an bend things and can result in a runaway engine. In my opinion  not worth therisk.

If the blower has a low boost multiplication rate and you add liquid coolant (alcohol water blend) just before the blower, you can retain good if not perfect response and eliminate engine runaway risk.   

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

If you use a turbo wastegate for the supercharger air bypass, any pressure spike will force the poppet valve off its seat (against the internal spring), and act as a fail safe pressure relief valve, up stream of the throttle.

This will still work, even if one of the two pressure control hoses to the wastegate diaphragm fall off.

All production cars must be fitted with dual throttle return springs these days, and that should go a long way to avoiding a stuck open throttle.

A stuck open throttle can be a frightening experience in any car. But on a really high powered forced induction car it can be absolutely terrifying.
 

RE: Twincharging with Screw-Type SC instead of Roots

yes.  it's wise to have a kill switch (coil or fuel) within reach so you don't chance losing steering if she's bouncing off over redline.   anyone ever have their gas pedal catch on the floormat?  

A throttle body in front of a twin screw type charger is not such a bad thing.   These chargers are quite loud, even at an idle.  this type of setup also requires plumbing to be rigid because everything downstream of the charger will now also be under vacuum.  referencing my setup, throttle response is immediate at any rpm, in any gear.  it's great because there's always immediate boost available.   this is the exact opposite of my other car, who's turbo doesn't spool until 4k, but will blow 20psi all day.

I'm going to take the TSI's side of the table for arguement's sake.  please tear me apart so we can find it's shortcomings.

I think control of the SC clutch and bypass valve are easier than we may thing.  in this scenerio, the TB would have to stay on the manifold because it can't be upstream of the turbo, so it may be a little noisey (maybe baffle the intake?).   any standalone management system could handle it and even manage duty cycle if you wanted partial openings.   I simply see the SC bypass being closed unless turbo is making boost, then it would need to open fully. can't see when it would want to be partially open, you would lose boost from SC.  (off beat, supposedely these clutched eatons can freewheel? ).  for oem mangement, you'll likely be restricted to electro or mechanical vacuum switches.. hmm.

now for the bypass, a throttle body with TPS could provide position feedback to a servo of some type.  or, a drive by wire TB could be rigged to work.  anyone have any other thoughts for other off the shelf valves or even check valves that would work?

knowing the sc makes X psi and the turbo makes XX psi, management would disengage the SC 'circuit' (pulley and bypass) when boost levels reach desired turbo levels.  without management, this could be done with a pressure switch.

you'd also have the ability to turn the SC off, and you'd drive no problem.  great for being quiet when you don't need it.  in cabin SC on/off switch.. sweet..

back to the thread starter, if clutched lysholm style chargers were available, if that's even possible because it does take alot to spin it, my opinion is it would be superior to the eaton.   but the clutched m45 or m62 off the MB is very attractive for this application.

great reading this thread, nice to meet everyone, and I'm curious to see what we all build!  

RE: Twincharging with Screw-Type SC instead of Roots

o/k so let's assume your supercharger is making 15 psi of boost, and you decide to suddenly de-clutch the supercharger "to reduce losses" once the turbo winds up.

What do you think will happen to the engine induction air pressure, if the supercharger that is contributing significant (probably most of) the flow and pressure to the engine, is suddenly switched off?

Why not completely bypass the turbo exhaust turbine as well "to reduce losses" even further ?

But seriously, once the supercharger is creating positive boost pressure, there is NO WAY you can just switch it off.  It would feel like disconnecting half your spark plugs.

The only time you can smoothly clutch, or de-clutch a supercharger is when it is already completely bypassed, and producing zero boost pressure. That would only be the case at engine idle and very light throttle during constant speed highway operation.

If it is already totally unloaded, why de-clutch it ?

A throttle body in front of any positive displacement supercharger just turns the supercharger into a giant vacuum pump.  If you think large vacuum pumps consume zero drive power, you would be mistaken. Throttling the air into a supercharger does not unload it, far from it.

It will run hot and noisy throttled at the intake. My own experience trying this, is it will cost around ten percent in wasted fuel creating all that unwanted heat and noise.

Every production supercharged engine I am aware of uses an air bypass around the supercharger that opens on closed at light throttle.

What you need to do is relieve the supercharger of all back pressure. That will unload it, unless it is a screw blower with internal compression.  Unfortunately there is no obvious way to completely unload a screw blower. But a roots blower can be completely unloaded. Imagine just the rotors spinning around in open air with no outer casing, to get the general idea. This ability to easily and completely unload a roots blower without de-clutching is a considerable advantage for a road car, and should not be dismissed lightly.

Forget about unloading the supercharger under boost.  It will work about the same as completely unloading a turbo by fully opening the wastegate when up to full turbo boost.

And another potential problem that may be less than obvious.  If you de-clutch a positive displacement supercharger when it has positive boost pressure at the discharge, it will run backwards at a million explosive rpm, venting all the up stream boost backwards through the supercharger. That not only makes a very nasty noise, it can break things.
 

RE: Twincharging with Screw-Type SC instead of Roots

Supercharger first, turbo second arrangement being discussed here.

If the supercharger is making boost from idle speed, the turbo will not be. As the engine accelerates and the turbo spools up, the turbo compressor starts accelerating and developing a pressure ratio. This automatically draws down the discharge pressure of the supercharger (Not to the point of being a vacuum, just to the point of the pressure ratio becoming lower.) Eventually it will draw down the supercharger outlet pressure to atmospheric. Under load, that's when the supercharger can be bypassed (and de-clutched at your option).

The tricky bit is what to do at part load and idle. The supercharger must be bypassed in these conditions.

With OEM fully-mapped engine controls it's not a problem to duty-cycle or modulate the bypass valve depending on RPM and requested engine load.

My comment about supercharged applications normally having the throttle before the supercharger is not based on OEM, but rather based on the traditional V8 with a supercharger sticking through the hood and a set of carbs on top ... The other way I've seen it has the throttle after the supercharger, but the supercharger is centrifugal (non positive displacement); lots of kits for Mustangs etc are like this. I don't know if they do any bypassing, but I doubt if efficiency was a prime consideration in either case.

RE: Twincharging with Screw-Type SC instead of Roots

Yes indeed.  The typical hot rodder and drag racer does not fit a roots blower to his engine to increase fuel mileage (smile).

So to him, the only matter of any importance is the standing quarter mile acceleration time at wide open throttle.  What it does at part throttle down the highway is of absolutely no interest whatsoever.

But practical every day street engines are a whole different ball game, especially now gasoline is becoming expensive, and soon perhaps scarce too. Throttle response, drivability and economy make the whole game more difficult.

While there are many weird and wonderful configurations possible, some are going to be fairly difficult or maybe impossible to get the bugs out of.

RE: Twincharging with Screw-Type SC instead of Roots

so it looks like switching off the SC is a delicate task.  so yes, any pressure between the SC and turbo must be bled off before disengaging to 1) prevent it from spinning backwards and 2) enable a smooth disengagement.   this could be done by opening the SC bypass before the SC is disengaged once the turbo has spooled.  this is very tricky as we don't want to combine boost that would result in a boost spike.  with my Wintec II, I could start opening the SC bypass when boost levels exceed the turbo's 15psi (like 16psi), then immediately after atmophere is met between the two, the SC could be safely disengaged without notice.  RPM would be around 4k.

I think we need to make an assumption that stand alone management is required for this.  it's just too tricky to do this with vaccuum switching..  

As for number's i'm thinking, expecting no more than 8-10 psi from the charger, and the sky is the limit for this turbo (running 15psi street).

at low RPM/idle or when boost is not needed, a diverter valve would open by vac. in the intake creating a loop for the SC's flow.    and this would be in addition to (if it's even necessary) to a BOV between the turbo and TB.  SC doesn't necessarily need to be bypassed at idle or low RPM, it just needs a way to blowoff/divert pressure.

in regards to bypassing the turbo, I would expect it to spool a little faster/earlier with 8psi coming into it.  thoughts?

back to TB location, no matter where the TB is, you're not going to unload a screw type compression (I think you confirmed my suspesion).   No matter where the TB is (pre or post charger), you still need a diverter or boost return.   It's not a vaccuum pump even though it may appear to be with an upstream TB closed.  it may be under vacuum, but it's still moving air around unrestricted in a loop and not drawing any more power than if the TB was downstream.

definately not an easy thing to do, but not impossible as VW has it currently in production.   but definately alot better than pushing a turbo THRU an eaton as most VW tuners are doing today.  

RE: Twincharging with Screw-Type SC instead of Roots

All the problems have been solved, some very nice twin charging systems have now been built all over the world.  
Yet people still try to complicate things unnecessarily, and why that is so, baffles me.

Aftermarket engine management will definitely be required, because the fuel, and especially the ignition timing requirements will differ hugely from what came fitted to the original normally aspirated engine.

Here is how to do it.

1/ Leave the throttle on the plenum in the original position !!!

2/ Mount the roots type supercharger, and the drive system to the engine. The car will still be drivable while you do this. It is a big job.

3/ Fit an air bypass system directly around the supercharger using an external turbo wategate. Connect up the wastegate actuator to work from the differential pressure drop across the throttle body.

4/ Connect the supercharger discharge to the throttle body via the largest air to air intercooler that will fit in the available space in front of the radiator.

5/ You now have a very nice, really tractable supercharged engine with excellent drivability and fuel economy. It will be very well behaved, but will probably lack extreme top end power.  Nevertheless it is an excellent start.

6/ To twincharge, just install a turbo to that engine in the usual way. Turbo compressor discharge goes straight into the supercharger intake. Exhaust wastegate sensing pressure comes from total combined boost after the supercharger.

This is a PROVEN system.  
It is SIMPLE as it can possibly be.
And it works extremely well, as many people that have built it this way all agree.

If you want to try doing it some other completely different way, I wish you luck.  

RE: Twincharging with Screw-Type SC instead of Roots

Holy defensive.. the system you just described is common, and proven, however I'm trying to discuss alternatives to it.  On the table here is basically replicating the VW TSI design, which is in production, so spare me the over-complication nonsense.

first of all, TB positioning is getting confused here.  for the TSI replication of a twin charged design, the TB stays on the plenum downstream of the chargers.   For a twinscrew ALONE, I'm not aware of any losses associated with a TB positioned upstream of the charger.  The charger is not under any more continuous load than with the TB downstream.  there is still a recirc.   this is extremely common with lysholms due to their noise.  I'm doing it too and have no temperature or efficiency issues.

for the record, I already have a Lysholm twin screw blowing a 2l 16v motor.   as you stated, drivibility and fuel economy is excellent.  I'm not making any changes to this car. It's running OEM digi-1 boost aware management with a custom chip, so aftermarket management is not necessarily required for boosted motors; however, it's I/O's will help with the twincharged specific issues of the TSI design.  

my other '87 is the same 2l 16v motor, but with a big turbo.  it's an all or nothing kind of setup spooling at 4k. 230whp in 2200lbs.   this is the setup that needs a supercharger for low end which is lacks now.   

Also have a supercharged cabriolet, a small turbo type I scirocco, and completed countless other boosted swaps.  not looking for you to teach me how to build a setup we are not even talking about.

now as far as being constructive, one of your comments caught my attention.  

If it is already totally unloaded, why de-clutch it ?

agreeing that the charger must be unloaded to de-clutch it, this brings up another issue.  when to re-engage it.   also agreeing our target is street driving, right?   All of my cars are daily drivers and I've never been to the track.   so this would mean re-engaging it between shifts if and only if the next gear RPM will be lower than the turbo spool RPM..  now here's a tricky area!!  

complicated, yes.. impossible, no.   I know we could build the system you described with a turbo blowing a eaton (didn't I mention I didn't want to do that in the last sentence of the previous post? ? ), but I found this thread researching the TSI and thought it looked open for discussion.   believe the first thing I said was I'm taking the TSI side of the table...   maybe you need to take a closer look at the TSI setup..

RE: Twincharging with Screw-Type SC instead of Roots

one more quicky -
why disengage the charger under light load/low RPM?  I would want it spinning and ready to boost.  it would be recirculating because of the diverter.  once the TB is open for accelleration to the point where there is no vac, the diverter/bov closes, the charger is already spinning, and you get immediate boost.   you're just closing a diverter to get boost.
 

RE: Twincharging with Screw-Type SC instead of Roots

I'd have say that this thread has been very fruitful.

But the way I've decided to do it is way Warpspeed suggests, Sc then Turbo with two wastegates controlling the boost. And Possibly Using Two Intercoolers, the one might be a charger cooler.

I'll use the Sc first and how it behaves then i'll add  the turbo.

RE: Twincharging with Screw-Type SC instead of Roots

no agruement that setup will work and has been done before, but it suffers from the same fundimental problems  where all intake air passes thru both chargers.  this means compressing and/or displacing air twice throughout the entire RPM band.  needless to say, heatons are best for their mid-range performance, yet it must run past its efficiency range in this setup.  Again, this is an option, and you'll make gobs of HP thoughout your nice TQ curve.. TC FTW.  

the point of the TSI engine is to allow both compressors to work within their efficiency range, and for one charger to not effect the other charger, almost like it's not even there, eliminating almost all paracitic and flow related losses.   This is a breakthru in twin charging and I believe VW is the only one doing now.   they get 168bhp from a 1.4l motor! from the factory!   that alot of power from a little package, efficiency at it's best.  

Just looking for a healthy discussion on understanding the concepts and workings behind the latest, production automotive twincharged setups made by VW or whomever.  

RE: Twincharging with Screw-Type SC instead of Roots

Yes all the intake air passes through both chargers in series, all of the time. And trying to get around that somehow, will not gain you much. But it will surely increase complexity, and introduce some other rather interesting little problems that will likely keep you occupied.

Two stage compression does not mean the compressed air will be twice as hot as many people sometimes expect.  It is compressed twice, but each stage only provides roughly half the total compression.  The net effect is not going to vary by much, no matter how this compression actually takes place.

By far the more important issue is providing sufficient intercooling AFTER all this violence has been inflicted upon the air, (by whatever means).

If intercooler capacity is made generous, the efficiency of compression becomes hardly significant at all. If you can reduce induction temperatures sufficiently, the engine will be very grateful.  And it will happily show it's gratitude by providing a little extra supercharger drive torque, and tolerating a slightly higher turbine intake pressure.

So to a great extent, a less than wonderful supercharger and turbo combination can be offset by fitting the worlds largest intercooler. At the end of the day, what comes out of the flywheel is what matters.

Hoof, use one monster intercooler last thing after the supercharger. Cooling the air before the supercharger is not  of any real practical advantage. This is especially true if it means the final intercooler must be made much smaller, which is often the case.

The supercharger can handle hot air just fine, it will be fairly dense hot air, but that is no problem.  Just alter the drive ratio to get the required pressure increase. A few extra supercharger rpm is no big deal. Place all the charge cooling last, and pull out as much heat as possible there.

As for clutching and de-clutching, that too is something of very doubtful value.  The manufacturers do it for two reasons. The Toyota blowers are rubbish, and wear out extremely fast if continuously driven. They also run very hot if driven continuously. Toyota clutch their blowers simply to make them last.

I am told Mercedes clutch their blowers for noise vibration and harshness reasons only. The clutches are a big problem, they operate under high stress, and figuring out an acceptable  clutch control strategy to do this is far from simple.

Just use a solid well designed supercharger (most are) and keep it spinning. It simplifies things greatly, and there is no disadvantage except perhaps some slight continuous mechanical noise from the drive, especially if a toothed belt is used. Use a silent multirib belt if at all possible.
   



 

RE: Twincharging with Screw-Type SC instead of Roots

If you intercool between compression stages your max ideal power savings are on the order of ~0.5 hp (assuming a 2.0 L engine with 90% vol eff at 7000 rpm and one bar of total boost).  You will get better heat transfer with only one intercooler after both stages because your temperature differential will be greater so you should easily make that 1/2 hp back with a cooler intake charge (as long as the supercharger can handle the hotter air).

RE: Twincharging with Screw-Type SC instead of Roots

The supercharger will usually be mounted right behind the radiator, and often right up close to the exhaust manifold.  The whole engine bay will be as hot as hell, and the supercharger will rapidly heat soak to perhaps 85C or more.

What air comes out of the turbo will also be pretty well "roasted" even under non boost conditions. Just feed the turbo straight into the supercharger intake.

It makes for a nice neat compact installation, with minimum pipe volumes, and don't worry about high interstage air temperature, there is nothing you can really do about it anyway.   

RE: Twincharging with Screw-Type SC instead of Roots

You still have the real danger that if the blow of valve sticks closed, you have a runaway engine if it then bends the throttle shafts and sticks them part opened.

A closed throttle downstream of a positive displacement pump builds pressure until something relieves the pressure. If the BOV sticks, something else gives.

If it were mine, I would fit a burst panel as well as the BOV so the burst panel broke well before the throttle shafts bent. A single valve safety device really is jst not good enough when the consequences are considered.

Two BOVs are also not all that good re safety as if one fails the other operates with no real indication to the driver. It can stay that way undetected for years. A burst plate is very obvious when it bursts. The burst plate should be upstream of the throttle for obvious reasons  

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Twincharging with Screw-Type SC instead of Roots

Or just leave the IC piping clamps loose :).  A good point though, Pat.

RE: Twincharging with Screw-Type SC instead of Roots

An external turbo wastegate is pretty fail safe.  The spring holds it closed. There is nothing there that can obviously fail and jam one shut. The wastegate is also working with with clean air, not red hot exhaust gas. The bypass is also in fairly constant motion (with all throttle movement), which should discourage sticking anyway.

A bursting plate is not a bad idea. Drag racers have been known to use light gauge aluminium cut from a drink can  to work as a bursting plate on big gasoline and nitro filled roots blowers. Blower explosions can be pretty expensive.

For the truly paranoid, a pair of wastegates working in parallel would offer another solution.

My own experience with extreme pressure spikes, is that either a hose blows, or the supercharger drive belt first slips and then shreds.  

RE: Twincharging with Screw-Type SC instead of Roots

I am only paranoid when the consequence of not being so can be fatal.
I agree belt or duct failure are likely before throttle shaft, but how well you secure a pipe or how much overcapacity drive has is a fairly inconsistent method.

I have seen blowers with direct crank drives and gear drives. It would take a lot for that system to fail first. Just because belt drives are by far the most common now, I would not automatically presume it in the absence of alternative information. I know it's a stretch in this case, but others read what we post here.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Twincharging with Screw-Type SC instead of Roots

check it:
http://mr2.com/TEXT/SuperChargerInfo.html

looks like toyota is no stranger to SC clutches and bypass valves.  Even though some may think the setup stucks, it has a lot of merit considering it was done at the OEM level in 87-89!  infact, it's described to be similar to, if not actually being, the eaton type onboard bypass/wastegate.

it may not seem like bypassing and disengaging a SC would not offer much gain, but it's one more piece that add's to overall efficiency/performance of the motor, and it's happening now more often than not on OEM vehicles.  Here's how I look at it:  I know how much power I currently make with the turbo, and I don't want to lose any of it.   ie, once the turbo spools, I want the same unrestricted, fresh, cold air that I get now w/o a SC.   It's a hefty wish, and has warts, could be done other ways, but I've been bitten by the TSI bug.

monster fmic is a must.  Not a big fan of a/w ic's because of all their damn components.  (ha ha :)  My plan is the existing monster fmic between the turbo and TB/engine.   The little TSI uses an a/w IC in the intake manifold. how compact.

 

RE: Twincharging with Screw-Type SC instead of Roots

Nobody has referenced the best old thread in this one yet, so here it is - thread71-174690: twincharging estimated results.

I'm new here, I found that old thread on Google while researching the possibility of twincharging my car vs a bigger blower vs straight turbo.  It is the best technical discussion i've ever had the pleasure of reading in any forum on any topic I think, and I thank all who participated - especially Pat and Warpspeed - for the fantastic information.  I am DEFINATELY going twincharged now.  Maybe I can contribute a little, too.

It seems to me after much looking around, that starting with a supercharged engine or an engine for which well developed supercharging kits are readily available rather than a turbo motor would be a far simpler begining point.  Fabbing up a turbo system involves an exhaust manifold flange and some pipes (okay not really, but it IS easier) and intercooling should you desire it is simpler.  Adding a supercharger involes a custom intake mani and mounts, removing something or finding room for the extra pulley not to mention finding a correct size belt and new tensioner settings for the extra drag - and now you get to cool the air you compressed, which is a lot more involed than a front mount air-to-air common in a custom turbo setup.  I mention this because in subsequent threads I see a lot of people talking about adding a blower to this or that turbo motor for a twincharge, and that seems overcomplicated to me.

I'm starting with a great ice of work, the GM LSJ EcoTec.  I wish to bring in a new (I hope) idea to the twincharging discussion, that of using a remote-mount turbo for the system.  It seems to me that this would have several benifits.  Firstly, as remote turbo guys are always saying, cooler operating temps and less heat transferred to the compressed air.  Since we're compressing it again, cooler to begin with can't possibly hurt.  Secondly, we can run a real header system before the turbine.  Yes, the positive action makes this unecessary per se, but it occurs to me that in combination with a properly proportioned wastegate mounted near the front of the system and well before the turbine, further "tuning" of this complex exhaust equation becomes possible.  Just a thought.

Lastly a question.  The discussion has focused on a lesser pressure blower fed by a higher pressure turbine for the most part.  I feel that keeping my blower PSI up (stock is 12-12.5) should make for stronger low end response, and blowing a few extra PSI at the top end via the bigger than normal turbo up top would flatten things out.  Maybe less peak power this way, but a much flatter curve.  Correct me if I'm way off here.

The plans forming in my head now would invlove a GM stage 2 type arrangement bumping the redline of my 2.0 to 7k rpm, spinning the blower slightly faster with a slightly smaller pulley delivering 15-ish known PSI, and affixing a GT30 or 35-ish turbo out back with a long tube header system and high-velocity tuned exhaust with a custom wastegate mounted up front to make the motor think the exhaust is a lot bigger once the turbo is up to speed - reducing overall backpressure and keeping things cooler and happier.  I'll take a hit on overall pressure, I don't think I'll be starving for power, LMAO.  The existing HPTuners suite for the LSJ would give me a fairly wide level of control over the fuel and spark without messing with standalone stuff, and the existing boost-bypass from GM makes that (very good) discussion moot for me as well.

I'm also thinking an E85 conversion makes for less overall thermal units of power, but more resisitance to the obscene boost levels and detonation for a lot less $$ than VP105, lol.  This will be daily driven on a fairly frequent basis!

Thoughts? Feedback?

RE: Twincharging with Screw-Type SC instead of Roots

Can't figure out the edit funtion yet?  LOL

Forgot to mention that I'd be thinking no more than 8 psi from the turbo, tops.  Based on teh excellent info provided previously, that should get me more than enough boost - I might keep it in the 4-6 psi range from teh turbo!  Just a little more up top where the blower gets out of it's efficiancy range.

Thanks for reading...

RE: Twincharging with Screw-Type SC instead of Roots

I'm a newcomer to this particular arena so go easy, but I do have a fair amount of experience with compound forced induction having successfully twincharged a 2.5L V-6 engine for a customer/friend in the past. I've tuned a few different twincharged engines over the the last 10 years and I'm also slowly doing another twincharge build on my own car, an '03 SVT Focus which is what has led me to this site.

What I don't understand is everyone's fascination with copying VAG's design and placing the blower before the turbo. VAG had the luxury of placing the induction components in whatever order they wanted and using an expensive servo operated valve along with complex control logic to fix the inherit flaw present in modern OEM engineering.........fuel economy. Their design takes a fairly old idea and uses every trick to reduce as much parasitic drag as possible even though an unloaded and bypassed Roots blower takes little power to turn.

I'm not an OEM (thank God) so fleet fuel economy ratings and accountants don't drive my design choices. My current list of intake obstructions (in order) is: filter, turbo, air to air intercooler, throttle body, blower, air to water intercooler, intake valves. The blower and air to liquid IC came assembled together in a purpose built intake manifold. The entire unit is mounted tidily on the back side (transverse front driver) of the engine. A fairly large heat exchanger (6"x24"x1") is mounted in the rear of the car with some duct work to supply atmosphere through it at speed and 6" fans at idle. A cast manifold couples the turbo to the head and the charge is fed through a medium sized FMIC. A recirculating (don't like the ricer psshhhht) bypass is used before the throttle body and the whole thing is tuned with a MAP based standalone. There are some other black boxes and variables thrown into the mix like water/methanol injection but they aren't related to the big picture here.

The whole thing runs smoothly with no compressor switchover drama. When the turbo comes up to full boost it simply blows through the supercharger without incident. The powerband is as predictable as any other turbocharged car. The blower makes the engine behave as a larger one and the turbo does it's normal thing. It's sort of like driving a 3.5 L. turbo 4 cyl instead of a twincharged 2.0 L.

RE: Twincharging with Screw-Type SC instead of Roots

Jamin you posted while I was writing.

It seems we're on the exact same track. I use an M62 roots blower kit which by itself put out 12 psi. The turbo is a GT2871R which is internally gated (unlike the GT30 or 35 you're planning on) the electronic boost controller is set for 8 psi low boost and 12 psi high boost. The engine is built so it swallows the high pressures without issue. The tires are only 215s though and even with a limited slip, the low boost setting is overkill. Granulated rubber on demand in the lower three gears.

You're absolutely right about using a kit solution for the supercharger. I wouldn't have liked the chore of intercooling a roots blower and fabricating mounts. As you can see from the pic, this kit made it very easy for me.

RE: Twincharging with Screw-Type SC instead of Roots

Scirockett,
Yes the Toyota supercharging system was way ahead of it's time in so many ways. The only real problem was the "economical" construction of the rather cheap and nasty strait two lobe blower, which is non rebuildable. The bypass system is excellent, but unfortunately it is not readily transferable to another vehicle, because of how the whole thing is integrated into a very complex inlet manifold casting. Functionally, it is well worth studying and copying. A truly great effort by both the bean counters and the engineers at Toyota.

Jamin2
Starting out with a supercharged engine is the only way to do it, either OEM, a commercial blower kit, or do it yourself.

Changing the pulley drive ratio and/or the turbine a/r enables you to set it all up to predominantly have either the characteristics of a supercharged engine, the characteristics of a turbocharged engine, or the best of both without the disadvantages of either.

Jamin, there is no edit function here. Once you hit 'submit'   there is no going back.

DigitalGT
Definitely on the right track with this.
I too am baffled by some peoples ideas about doing this in really strange complex ways that only introduce extra problems.

 

RE: Twincharging with Screw-Type SC instead of Roots

(OP)
Digital GT and Jamin2, do you guys have pics you can post up?

Digital GT, I couldn't see that SVT SC Kit that you posted up, the link didn't seem to work. Try this:

To include an image in your post:
]img http://www.mysite.com/images/happy.gif]
edit: Change the first "]" to a "["

RE: Twincharging with Screw-Type SC instead of Roots

Digital GT - I didn't go into details about teh engine I'm using, as I believe there's a fair amount of info out their about the LSJ.  We are on a VERY similar track, lol - the LSJ uses an M62 from the factory, blowing 12 psi pver a 9.5:1 compression ratio.  They designed a very trick intake manifold with integrated laminouva (sp?) air to water intercooling, and a barely adequate front mounted heat exchanger.  The intake mani doesn't flow quite as smoothly as we'd like, but it gets the job done.  Luckily my car is blessed with an abundance space between the front bumper mounts and the radiator, so plumbing in a larger HE is cake, with room to spare for an air to air for the turbo, a popular mod is the HE from a Mustang Cobra plumbed inline with the existing HE, don't evenbother removing it.  Good for 20 degree drop in IAT's.  Okay - too much detail, lol.

I would really like to hear more about the '28in that setup.  I was thinking GT28, but after reading up on the other thread I figured I'd jump a size or two, lol.  I've seen a GT30 (don't recall the trim) in action on a 2.4 liter four, and it made full boost by 3400 rpm - with 12 psi worth of blower, I'm guessing that GT28 ramps up REAL fast, lol.

Warpspeed - thanls for the quick and direct reply, it's exactly what I was needing - knowingthat either track works without problems.  this being my first blown car (I've owned many a turbo), I've become somewhat addicted to teh feel, lol.  I may, down the road, bore/stroke this poor thing to 2.5 litersand upgrade to a TVS blower (1.32 liters/rotation vs the M62's .962).  I want lots of low and midrange power, but with more total power than a blower alone cn deliver.  I was all but resigned to going turbo and dealing with the difference in power delivery.  I am now VERY excited to get this going!   
  

RE: Twincharging with Screw-Type SC instead of Roots

(OP)
Jamin2, I think that the GT2856R (commonly called the GT28R) is too small for a 2L (in fact that turbo comes stock on some OEM 2L so it's definately on the small side)

My car is a 3L V6, and twin turbo'd (so 1.5L feeding each turbo) and is being built for GT28RS (about 550rwhp).

Given that you will be running a SC for low down grunt, you no longer care about a quick spoolup turbo. On top of that, remember that you 2L running with a SC at 15psi is acting like a 4L N/A. So any GT28 is too small for your application!

RE: Twincharging with Screw-Type SC instead of Roots

I don't have finished pictures of my twincharged conversion yet. The car is currently on stands in my garage undergoing ANOTHER clutch replacement and the oiling system is being upgraded with a 2 quart oil accumulator, braided hose and an oil cooler.

I do have this shot of the blower though. Sorry the other link didn't work.

RE: Twincharging with Screw-Type SC instead of Roots

I need to replace the oil in the gear section of the supercharger, unfortunately after searching I can't find what type or viscosity ,mainly the latter ,to use can somebody please suggest a type of oil. Somebody suggested Diff Oil like a 85w 90.

Thanx

RE: Twincharging with Screw-Type SC instead of Roots

Manual transmission gear box oil. After all it is a one speed gear box

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

I wouldn't use MTX gear box lube. Several OEMs have supercharger lube designed specifically for Roots blowers. I buy mine from the local Pontiac dealership but only because it is the closest GM car dealership to my house. You want "GM Vehicle Care Supercharger Oil" and it comes in 4 ounce bottles. You need two bottles. Part # 12345982. It costs about $7 a bottle.

RE: Twincharging with Screw-Type SC instead of Roots

here's the response straight from Steve Padfield of Vortech Engineering: "[Vortech's] maintenance-free lubrication system uses engine oil that is pre-filtered and injected directly onto the drive gears. We chose this configuration as opposed to a `self-contained' setup because engine oil provides faster warm up, excellent reliability, and superior cooling. The lubrication oil benefits from continuous filtration, being routinely changed along with the engine oil (instead of an additional maintenance action). This system also offers the best opportunity for thermally stable operation. Vortech firmly believes this is the best method to feed and care for a supercharger."

Any Thoughts on the matter?
 

RE: Twincharging with Screw-Type SC instead of Roots

Vortech intentionally designs their blowers around the idea of using the existing engine oiling system for lubrication. Magnuson, on the other hand, designs around a self-contained oil bath. I don't see a centrifugal blower as having smaller tolerances than a modern engine and, as such, see no reason why filtered engine oil (which is certainly good enough for the highly stressed powerplant) can't be used.

I'm a big proponent of using what the OEM recommends if for no other reason than to eliminate a warranty dispute later down the road. Obviously I leave myself very open to the idea of upgrading but sometimes mother really does know best. So long as the oil supply is post-filter and regular oil changes are made, I see no flaws in Vortech's logic. If it's good enough for the 100,000+ RPM center cartridge of a 1600° F. turbocharger, it's good enough for a blower.

That my humble grease monkey opinion. I'm sure someone else can geek it all out for you or reference some white paper somewhere to "prove" me wrong however. :)

RE: Twincharging with Screw-Type SC instead of Roots

I Know what you mean about getting blown by facts. Um I think they wanted the oil filtered because they were using tiny oil jets to spray oil on the gears. Possibly they didn't want them getting blocked.

I'll have a look to see how hard it is to adapt a oil jet system to the charger.

RE: Twincharging with Screw-Type SC instead of Roots

The gears are similar to gear box gears in design and operation. They don't know what they drive. Normal manual transmission gear box oil does work I use it in a 6:71 no problems I think it was 80 weight. I never paid that much attention. It was left over from oil I bought for a manual box I rebuilt about 20 years ago.

Regards

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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Twincharging with Screw-Type SC instead of Roots

Whipple and Opcon/Autorotor both recommend 15/50 or 20/50 synthetic motor oil for the gearboxes in the twin screw compressors.

 

RE: Twincharging with Screw-Type SC instead of Roots

Pat I can see where you're coming from in that they are just two gears costantly in contact and motion, and that Normal Manual Transmission oil would work. If I Were to use this then i would just change the oil regularly.

I'll try to find i similar rating to those two types of oil, but if i cant then im not gonna bash my head. At the end of the day Im sure it's a marketing sceme because people think it's a supercharger it SHOULD have exotic oils, fully synthetic will only do.

RE: Twincharging with Screw-Type SC instead of Roots

I have run synthetic engine oil in roots blowers with a sealed oil case for high mileages without any problems. The oil always stays very clean. The only danger is that if one of the seals leak, the fairly small volume of oil contained in the blower gear case may leak away unnoticed. If you are a typical hotrodder or enthusiast, there is probably not much chance of that ever happening.

There is probably still an argument for using the main engine oiling system in an OEM application, where the blower gear case oil level may never get checked. At least the blower is always full of oil, and it gets changed when the engine oil is changed.

At the end of the day, I don't think it really matters either way.    

RE: Twincharging with Screw-Type SC instead of Roots

Crankcase oil has a much harder life than gearbox oil due to blow by of combustion products.

A blower gearbox may see some oil dilution from unburned fuel depending on where the fuel is added to the system. This applies to all oil types

 

Regards

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RE: Twincharging with Screw-Type SC instead of Roots

The best oil is the oil you change. Regularily.  I put a B&M minicharger on a small block Chevy, back in the mid 1980's, and about a year and a half later, the customer calls me up saying the blower tossed the drive belt and the unit is siezed.  I ask "when did you change the oil last"?  Bingo, he never did. Rebuild was thankfully light, and from then on every 5000km, the oil was replaced with regular 10-30 engine oil with good results.  On my Thunderbird SC, I was using genuine Ford supercharger oil, when I discovered that Ford's supercharger oil seemed to be exactly the same as aircraft turbine engine oil, (Unscientific smell, and finger feel test.) and since then I've used Esso-2380 turbine engine aircraft oil in the supercharger gear sump, with excellent results. (The car now has 265,000km on the original engine.)  A lot less expensive per litre too.

j79guy

RE: Twincharging with Screw-Type SC instead of Roots

(OP)
Well, just a short update on this one :) today I bought an EJ255 which is the 2.5 litre turbo engine as used in the Subaru WRX 2006+ models

Have also decided that I won't do an engine transplant, but I'm going to design a car in Pro-E software and then build it

:) Also, I'm stoked at the price - I got it dirt cheap! $300AuD which is about $200 USD
how cheap is that! spun bearing or something, which doesn't matter cos I'd rip it open anyways~

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