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!
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
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
Anyone done this or know of this having been done?
RE: Twincharging with Screw-Type SC instead of Roots
j79 guy
RE: Twincharging with Screw-Type SC instead of Roots
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
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
j79 guy.
RE: Twincharging with Screw-Type SC instead of Roots
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
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
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
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
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
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
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
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
RE: Twincharging with Screw-Type SC instead of Roots
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
RE: Twincharging with Screw-Type SC instead of Roots
I am really fed up with doing your homework for you. READ THE PREVIOUS THREADS if you expect any more help from me.
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
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
PJGD
RE: Twincharging with Screw-Type SC instead of Roots
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
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
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
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
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
PJGD
RE: Twincharging with Screw-Type SC instead of Roots
This stuff ain't simple, no matter which way it's done.
RE: Twincharging with Screw-Type SC instead of Roots
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
RE: Twincharging with Screw-Type SC instead of Roots
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
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
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
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
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
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
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
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
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
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
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
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
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
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
RE: Twincharging with Screw-Type SC instead of Roots
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
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
RE: Twincharging with Screw-Type SC instead of Roots
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 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
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
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
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
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
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
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
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
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
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 do have this shot of the blower though. Sorry the other link didn't work.
RE: Twincharging with Screw-Type SC instead of Roots
Thanx
RE: Twincharging with Screw-Type SC instead of Roots
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
RE: Twincharging with Screw-Type SC instead of Roots
Any Thoughts on the matter?
RE: Twincharging with Screw-Type SC instead of Roots
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'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
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
RE: Twincharging with Screw-Type SC instead of Roots
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
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
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
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
j79guy
RE: Twincharging with Screw-Type SC instead of Roots
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~