Twin Charging a Honda CRX
Twin Charging a Honda CRX
(OP)
I having a moment of madness and considering twin charging a 1988 Aussie model CRX.
Aussie model has the DOHC D16A8 engine and factory A/C and P/S both of which I must retain.
The plan would involve a second hand Toyota SC14 roots type blower.
I already have a turbo being a brand new Garrett GT2859R-707160-9. M24 cast on compressor.
Ball bearing, water cooled bearings.
Compressor is 44.5 inducer, 59.4 exducer, 56 trim, 0.42 A/R
Turbine is 53.8 wheel dia, 62 trim, 0.64 A/R
It has an internal waste gate but I also have a 41mm Chinese external wastegate.
The turbo is correct size for my ambitions turbo only, but probably a bit small for twin charged.
Aussie model has the DOHC D16A8 engine and factory A/C and P/S both of which I must retain.
The plan would involve a second hand Toyota SC14 roots type blower.
I already have a turbo being a brand new Garrett GT2859R-707160-9. M24 cast on compressor.
Ball bearing, water cooled bearings.
Compressor is 44.5 inducer, 59.4 exducer, 56 trim, 0.42 A/R
Turbine is 53.8 wheel dia, 62 trim, 0.64 A/R
It has an internal waste gate but I also have a 41mm Chinese external wastegate.
The turbo is correct size for my ambitions turbo only, but probably a bit small for twin charged.
Regards
Pat
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RE: Twin Charging a Honda CRX
I hope there will be room for a sandwich plate water to air inter cooler. There should be enough room. This keeps the manifold inter cooler volume real small so throttle can be on the inlet to the blower.
Turbo would be on a mass produced after market cast iron manifold. Tried and true, reliable compact fits with A/C and P/S and stock radiator location.
Air to air inter cooler would be front mounted between grill/bumper and radiator to cool air from turbo before the SC-14
Just to prove I must be stark raving mad, I am also considering propane liquid injection as fuel.
I already have a Honda ECU with a fully programmable chip installed. These allow full remapping of fuel and ignition tables and retain all OEM features.
The engine will be bored to 78mm (from 75mm) and stroked to 94.5mm (from 90mm) with a raised deck via longer thicker iron sleeves and an aluminium closed deck plate about 12mm thick to holds it stable with longer 150mm rods (from 137mm) giving 1.59:1 (from 1.52).
The rods will be after market H beams, the pistons will be after market forged and the crank will be Honda D17 forged steel.
Head will be mildly ported with 1mm bigger 1 piece SS valves and stronger springs. Cams will be stock as these engines already make power to 7000 rpm stock. Lobe centres will be spread a few degrees as a starter
Regards
Pat
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RE: Twin Charging a Honda CRX
The questions are:-
Has anyone had any real experience with a Toyota SC-14 with the clutch removed so it runs permanently coupled to the crank.
If so, how fast can you reliably turn the blower.
Do they perform better with the rotor coating or stripped off.
Do the bearings stand up. Can they be improved. Will I need to make new end housings to get reliability.
Will water injection before the blower help by lubrication, sealing and cooling the rotors.
Has anyone made better rotors, like 3 or 4 lobe high helix rotors like the Eatons. How much advantage will better rotors be on a twin charged system where high speed efficiency does not matter so much
Would the second inter cooler (the water to air one) be necessary or advantageous with water injection. Probably not.
With say 20# boost at 60 deg C charge temp, on propane at I think 105 octane and excellent exhaust scavenging and good quench and tumble in the chamber what CR can I run. 8:1 maybe.
How wide is the drive belt on the SC14 Is it toothed or multi grove V belt.
Can a chain drive work and be narrower to clear the chassis and eliminate slip.
Regards
Pat
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RE: Twin Charging a Honda CRX
No direct experience with that particular supercharger, but a couple of thoughts on your proposed setup. I would keep the supercharger's role light and use it to help the transient response while letting the turbo do most of the actual boosting work. This is especially true of you want to delete the clutch and run the charger full time.
In a serial arrangement, you don't need a high PR in each stage before you get far more boost than your engine can handle. Also, in this arrangement, the more boost generated on the first stage heats up the charge even more and costs more compressor work for the second stage.
Turbo sizing is only a concern in view of what your power output goals are. That compressor you've specified can flow up to 26 lb/min at PR=2.3 with 70% efficiency. Placing it as the second stage will push the operating points - with inlet correction factors - to the left, making the compressor an effectively bigger unit than it really is. Turbo alone, you're good for about 220 BHP at 6000 RPM, as I've calculated with your given numbers in the below link assuming a BSFC of 390 g/kWh at maximum power and a pretty rich AFR of 11:1
http://1l2.us/bd_
Done right with the additional supercharger and some form of water/methanol/fuel injection, you may be able to raise that to 270 BHP. That assumes you run a pressure ratio of about 1.3 across the supercharger. I don't estimate more because you are turbocharger mass flow constrained and not boost pressure constrained (here you'd already be running about 28 PSI gravimetric).
Lotus placed auxiliary fuel injectors in the Exige 275E (tri-fuel flexible) upstream of the supercharger to give a charge-cooling effect. Gasoline in the fuel can also provide some lubricating benefits as well, but if you try this, ensure that the turbo compressor seals are compatible with the fuel draw-through. My simulation have shown though, that pre-compressor injection of any fluid pushes operating points to the right of the map, making you closer to the mass flow limit. Water/methanol injection - preferably as close as possible to the inlet ports - could certainly help also help with charge-cooling and retarding knock.
HTH.
RE: Twin Charging a Honda CRX
RE: Twin Charging a Honda CRX
are you familiar with VAG's 1.4 TFSI twincharging? I could find info for that setup for you. I believe TDIMeister could find it too.
RE: Twin Charging a Honda CRX
My experience with an SC14 was that they are designed for short term operation only. On the original engine, the clutch disconnects the blower drive except during short manic bursts of acceleration.
Hooked up to be driven constantly, my SC14 always ran hot, and the whole blower gradually become more and more loose and noisy, until mechanical sympathy forced me to retire it to the dumpster bin. I ended up wearing out three of these blowers one after the other.
As these SC14 blowers now only cost about $200 secondhand, twelve to eighteen months of service out of each one may actually not be such a bad deal.
These Toyota blowers are definitely not rebuildable. The bearings are a unique unobtainable size, and epoxied into the aluminium case. To get it apart requires pressing off both the helical timing gears together. Without the factory jig, you will never be able to press the same gears back on so they are both still a tight interference fit, and the rotors still correctly timed. So forget about any rebuilding. These are a throw away item.
An Eaton M90 is a far better designed and more robust piece of machinery, and only slightly larger. And if you could score an M65 "Kompressor" of a small Merc, that may be another option to think about, especially if space is at a premium.
All these modern blowers now run a multirib belt, which will be silent. Toothed 8mm pitch timing belts are going to whine, and some people really enjoy this characteristic sound, but not me.
An Eaton is robust enough to run continuously, and with a suitable air bypass system can be completely unloaded.
RE: Twin Charging a Honda CRX
Seems both components are correct size.
It seems an Eaton is a better option if I can find the space. I was thinking the SC14 was a lot smaller and lighter than the Eatons.
I have a budget for the turbo setup, but the twin charge would be extra budget and I expect an Eaton might blow that out of the water.
If the m90 is the onethat is std on the V6 Commodores, I think they are just to bulky and heavy and a reverse direction drive needs to be fabricated.
There is a kit from Jackson Superchargers (JSRC) for an M45, but they are for the single cam D series and are far from a bolt on and in my opinion expensive and poorly engineered and only make about 8# boost and have belt slip problems and manifold heat problems
270 hp is top limit for the drive train which is old enough for replacement parts to be a problem if I break them regularly.
Should I get a few SC14s and consider them consumables like brake pads or spark plugs.
Regards
Pat
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RE: Twin Charging a Honda CRX
It is going to be just as much cost and hours of work fabricating mounts, plumbing, and fabricating up a reliable drive system, and debugging, as for something much better.
Why spend $1,000 on parts to install a $200 blower that is not going to be up to the mark?
And it will eventually cost that, by the time you have built everything twice, shredded four expensive drive belts, and purchased several new drive pulleys to get the drive ratio where you want it.
All this is based on personal experience over a few decades working on my own supercharger projects, and mentoring other people's projects.
About 90% of the effort will go into building and debugging the supercharging part. Hooking up the turbo is trivial.
So I might suggest you just plan on fitting the blower first. That will keep you entertained for a surprisingly long time, while you sort out the multiplicity of issues.
The results of just fitting a low boost roots blower will be fairly disappointing for all the work and cash sunk into the project. Be mentally prepared for that...
It will run well, but it won't be the ball of fire you may have been expecting.
If you go the other way and fit just the oversize turbo first, it will go like the clappers (if you really thrash it), but the high boost threshold, and a very narrow power band will soon become really annoying if you drive the car in traffic every day.
But with the whole twincharge setup installed, the results will be purely magical.
It will be absolutely nothing like it was with either just the turbo or blower fitted, but something unique and totally different.
RE: Twin Charging a Honda CRX
The blowers where GM type on American V8 for drag racing with MFI and methanol. Most things where available off the shelf as the first few where SBC. I am doing a 430 odd CI Ford Windsor right now. That has been a bit harder to buy off the shelf parts for.
I will ask around about an Eaton off a V6 Commodore and see what turns up.
I know what to expect (or not expect) from a low boost blower so I will not be disappoint at that stage.
I'm thinking it is all getting to hard
Regards
Pat
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RE: Twin Charging a Honda CRX
There has been so much written lately in these forums about the combination of a positive displacement blower and a turbo (and it does seem to be a good idea) maybe some manufacturer should think about making an aftermarket blower/turbo in the one unit?
RE: Twin Charging a Honda CRX
Also ideally the air should be cool as it enters the roots.
The mounting of a roots is greatly limited by needing a stable strong mount to maintain belt alignment and tension while a turbo can be mounted pretty well anywhere you can run a pipe so long as the heat won't damage surroundings.
By combining them, you need to compromise several of the above.
Regards
Pat
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RE: Twin Charging a Honda CRX
The mounting and driving of the supercharger will be by far the most difficult obstacle to overcome. As I said earlier, the blower part will be about 90% of the whole project.
It is almost certain that other major engine accessories may need to be moved to make space, and that is what rapidly complicates the whole thing.
The turbo is physically quite small in comparison, and the adjustable orientation of both housings on the core make it quite readily adaptable.
My own preference is to not mount the blower right over the inlet ports, but to use the original plenum and throttle body as is, and fit the intercooler between the blower and throttle body. But as we all know, Pat has some very strong objections to that idea, so I will not pursue it here.
RE: Twin Charging a Honda CRX
I guess I haven't been around here enough... what is the crux of Pat's objections to that idea?
RE: Twin Charging a Honda CRX
I have softened my view on that a little, but would still want more than just a bypass with either a burst panel or an emergency shut down throttle like those fitted to Detroit diesels to shut down runaways as well as the bypass.
An idler and the blower over the gear box certainly helps with packaging and direction of rotation.
Blower over the inlet port certainly helps response if the throttle is before the blower.
I will not remove A/C or P/S. It would be hard to move them much, but I have a few options from stock parts as I have the D16A8 and a D17Z1. Although both D series, they have different crank snouts and crank pulley stacks and ancillary mounts.
I really want to do this but I need a nice compact little blower. The engine will use about 7200 litres/min theoretical displacement so I guess the blower needs to have a maximum output of 1000 litres/min at reasonable efficiency to give enough boost to add a little power and keep inlet pressure higher than the exhaust during overlap.
What is the minimum pressure ratio I need for good scavenging. I guess that varies a lot with turbo housing and AR and exhaust system back pressure. Is 1.3 usually enough or do I need the 1.5 you have already mentioned.
Regards
Pat
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RE: Twin Charging a Honda CRX
But a great deal depends on planned valve overlap.
That might end up as 8psi boost, with 4psi total exhaust back pressure in your typical big diesel two stoke truck.
A reasonable starting point might be a blower design pressure ratio of around 1.5 for this type of project.
Turbine back pressure is going to rob you of some of that, but it might be a reasonable starting point.
RE: Twin Charging a Honda CRX
M62 from series 1 3800 (bonneville, other GM's, 91-95) might be getting harder to find. Same size or slightly larger outlat than the T-bird M90, longer case due to the cast inlet.
Mercedes or Toyota M45
Methanol injection before the blower will increase VE and raise boost 1-2 psi, but also increases friction and parasitic losses. It's a fine line, I've done this on a GTP (3800 series II, L67). Very temperamental, it eliminated the detonation but wasn't much faster. Ran into belt slip issues when I shouldn't have.
RE: Twin Charging a Honda CRX
The M24 are the blowers fitted to the VW twincharger these days, if you can source one 2nd hand they are very expensive. If you are lucky you got one years ago from development of a certain Ethanol fuelled 1000cc RoCam engined Brazilian Ford ECOsport. You can still get them very cheap if you look from that source.
The Eaton website shows they are good to very high RPM's - due to small size.
M45 are fitted to BMW's mini and were very cheap 5 years ago but now not so. Still cheapest option.
One other thing to conider is the anti-lag effect of having the throttle downstream of the SC. Off-throttle the airflow is maintained through the turbo compressor (or Rp accross it).. You will LOSE this if you HAVE to have the throttle before the blower, and stall the TC each time you shut the throttle, change gear, tip out.
RE: Twin Charging a Honda CRX
That will make a significant difference to the importance of throttle response.
RE: Twin Charging a Honda CRX
A Blow off valve fixes the turbo blowing against a closed throttle just like in almost every turbo only application out there.
Response with throttle before blower is not an issue if the blower is mounted directly to a compact manifold with small plenum. Only last week I drove a T bucket Hot Rod with a 351 CI Ford Cleveland V8 with a 6:71, open plenum manifold and open plenum adaptor for the twin 4 barrel carbys. It smoked the tyres before the pedal even hit the floor when you slammed the throttle.
Regards
Pat
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RE: Twin Charging a Honda CRX
Like you say though, maybe response is good enough without that benefit, or maybe you are never off throttle whith this engine? Drag racing?
RE: Twin Charging a Honda CRX
It will weigh in at 1900# I expect and have 250ish hp and around 180 ft lb with 4WD. 1.8 litre 4 valve twin cam at 7# boost from the blower with no turbo at all should respond well enough. I expect the turbo boost will just be extra party time.
Regards
Pat
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RE: Twin Charging a Honda CRX
On the other hand, if you lay out the SC to blow into the TC and the SC is too small, then IT will be your limiting factor.
In either case, if you generate much the boost in the first stage without intercooling between stages, you generate conditions of high compressor work in the second stage, and this is more grave for the SC in the second stage in terms of thermal considerations and drive-belt skipping because you're asking for too much power transmission upon the belt.
The higher mass flow-rated device should ALWAYS be in the first stage.
RE: Twin Charging a Honda CRX
The second stage compressor work will be higher, (without interstage cooling), but the disadvantage is more theoretical than practical.
The only real limitation might be supercharger bearing and lubricant temperature. But if the interstage temperatures are objectionably high, it does not take much to pull down that temperature significantly, because the temperature differential across an interstage heat exchanger will be so high.
In any case, the supercharger will be well heat soaked, and running at under hood ambient temperatures anyway, so cooling the supercharger intake air temperature down below that, is a complete waste of time.
In practice, the blower is going to run hot, and a short burst of acceleration (say ten seconds worth) is not going to have any significant effect on the supercharger bearing temperatures.
Running it for several minutes flat out on a dyno might be different.
But on the road, cooking the supercharger bearings has never in my experience been a problem for anyone.
If you start to think about water pump and alternator bearings, and how reliable they are at similar operating temperatures, supercharger bearings will be just as reliable.
RE: Twin Charging a Honda CRX
It is capable of flowing 26 lb/min at PR=2.3 with 70% efficiency. Efficiency drops off rapidly without a significant increase in mass flow beyond this point.
The order of which device is put in which stage does not materially affect the attainable power output; the output will be determined by which ever device has the limiting *corrected* mass flow in the system -- mass flow remains constant because of the continuity equation but *corrected* mass flow across the device depends on inlet temperature and pressure doesn't have to be the same across both devices. A device in the first stage draws from ambient so that actual mass flow is approximately equal to corrected mass flow. In contrast, a device in the second stage has its inlet charge pre-compressed by the first stage, thus having the appearance of a "larger" device - meaning that the corrected mass flow is less than the actual mass flow by the correction factor that's proportional to T^0.5/P, i.e. the plotted operating points of corrected mass flow vs. pressure ratio on a compressor map will effectively shift toward the left.
RE: Twin Charging a Honda CRX
The flow of a turbo is largely influenced by any up stream flow restriction, they tend towards being constant pressure differential devices, with variable flow.
A positive displacement supercharger tends towards being a constant flow device. Restrict the outlet significantly, and discharge pressure can rise hugely.
RE: Twin Charging a Honda CRX
The purpose of the supercharger is twofold.
1) To improve response while the turbo is off boost.
2) To scavenge residual hot exhaust gas from the chamber during overlap.
As I understand it, a turbo is not positive displacement and it can allow air to flow past it with moderate resistance even if the wheel is stationary. It obviously offers less resistance as it increases rpm up to the point that it contributes to airflow.
A roots blower is positive displacement and it's displacement is absolutely tied to rpm. If it is stationary, no air flows. Although it cannot displace extra air from the turbo under boost, that air can have a higher density so mas air flow is maintained at the level of the turbo.
This means to a reasonable degree you get the mass air flow of the highest device. I know the turbo airflow depends on the head of pressure it pumps against as it is not positive displacement.
Regards
Pat
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RE: Twin Charging a Honda CRX
RE: Twin Charging a Honda CRX
Also car is stripped back to a bare shell and I need a few parts back on before I can do more measurements. It will take some time if it ever happens.
Regards
Pat
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RE: Twin Charging a Honda CRX
RE: Twin Charging a Honda CRX
This is not a bilge pump "electric turbo" so I hope you read past the first sentence!
RE: Twin Charging a Honda CRX
ANY turbo system has some lag.
A roots blower has virtually zero lag and that is the only reason I am considering the extra complication.
Regards
Pat
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RE: Twin Charging a Honda CRX
Bodge it all up, and you will then have an excellent idea of how to mount it, required drive snout length, and how to drive it, and available clearance.
When you know EXACTLY what you want, your supreme patience will eventually be rewarded on e-bay.
RE: Twin Charging a Honda CRX
That would seem to do the exact opposite of twincharging. Choking the turbine side down would increase exhaust manifold pressure, while twincharging would decrease it.
RE: Twin Charging a Honda CRX
RE: Twin Charging a Honda CRX
I have spent around eighteen months of totally wasted effort trying to get a VNT turbo to work on a gasoline engine.
Forget it !!!!!
Just build a twincharge system using a mundane garden variety roots blower, and a suitable modern ball bearing turbo, and it will absolutely KILL any straight turbo engine in every single respect.
Strong words, but anyone that has ever tried twincharging, or driven a twincharged vehicle knows exactly what I am talking about.
RE: Twin Charging a Honda CRX
As far as I am aware the only (current) production SI engine that uses VGT turbine technology is Porsche's Flat-6 Turbo. They changed some materials to give lower thermal expansion, and if you look at the turbine side a/r, it is quite large....
RE: Twin Charging a Honda CRX
Now the theory goes, that you can close the vanes right up and get an incredibly small a/r and the turbo will spool up at very low rpm.
The engine simply does not like seeing 80psi+ exhaust back pressure at wide open throttle low rpm.
The theory also goes that you can open the vanes right up and get massive low restriction exhaust flow.
Again all you get is massive exhaust back pressure at the top end. The reason being you are trying to force ALL of the exhaust gas through the turbine. It just goes into sonic choke and the power curve hits a brick wall.
Not even Garrett could make it work on a gasoline engine.
If it did work well, Garrett would be selling them instead of their excellent ball bearing turbos.
These VNT turbos have been around for decades on diesels, everyone has tried, only Porsche have been able to get it to work after massive complexity, and adding twin wastegates and a lot of electronics to control the vanes.
Twincharging is vastly simpler to control and get working, the results will be infinitely better, and anyone can do it.
RE: Twin Charging a Honda CRX
Regards
Pat
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RE: Twin Charging a Honda CRX
What type of vane position control did you use? What type of VGT mechanism did the turbo have?
Sorry Pat, if this is a bit OT, I will start another thread.
RE: Twin Charging a Honda CRX
the other is that , if you run 250 bhp on the blower , how can a 260 bhp turbo add anything ?although ,without looking at the map , id expect a 45mm inlet to run around 310 bhp .its still not much of a gain ..i feel a bigger compressor ,and a much bigger turbine is needed .
remember ,as im sure you allready know ,your ex gas quantity is greatly increased by the blower .something in the 50mm comp inlet sort of size ,and a gt 30/35 size turbine maybe .
regards
robert
RE: Twin Charging a Honda CRX
Building exhaust turbine wheels that stand up just fine to the extreme EGTs experieneced in gasoline SI engines is not a problem.
But you are suggesting the exact same materials when used for the stationary vanes are not good enough?
I don't think so.
This is all way off topic, I suggest you start a new thread.
RE: Twin Charging a Honda CRX
I'll post up some info in a new thread.
RE: Twin Charging a Honda CRX
A lot of the diesel turbos aren't going to last forever if you throw them on a gas engine, but that doesn't mean material limits are impossible to overcome.
RE: Twin Charging a Honda CRX
Getting it to work at all is the problem.
Might I respectfully suggest that you have never yourself fitted one of these turbos onto a gasoline engine, and tried in vain (sic) to make it work.
Lots of other people, including myself have put enormous effort into it, and we have all very quickly discovered the same things.
And as a matter of interest it is never the vanes themselves that jam up as you seem to think. It is the circular sliding vane actuating ring that links all the vane toggles together. That jamming problem comes from gradual exhaust deposit buildup (mainly lead), it is definitely not a materials related or heat problem.
In diesels these deposits are oily, in a high mileage gasoline engine they are as hard as concrete.
Unleaded gasoline goes a long way to reducing hard exhaust deposit buildup, which is probably why Porsche have never suffered from well known jammed vane problem.
I know you don't believe me, but these VNT turbos have been around for over thirty years. Where are all the winning race cars using this variable vane technology?
RE: Twin Charging a Honda CRX
It has been about 10 years since leaded fuel was allowed in Aus except for aircraft and a very few special race events. Even the V8 Supercars use unleaded.
Regards
Pat
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RE: Twin Charging a Honda CRX
But the VNT turbo has been around on diesels for decades.
But twenty or thirty years ago, the hard very dry exhaust deposits usually eventually led to vane jamming problems in high mileage engines.
The Japanese have been pouring vast amounts of money into developing turbo production engines for a very long time, and not a single variable vane turbo anywhere to be found. Ask yourself why is that?
As a matter of interest the race winning Formula One Honda TAG turbo engines used a pair of VNT turbos. But then the required power band was very narrow.
The Honda engineers know all about variable vane technology.
But no variable vane production Honda road cars ever surfaced.
And those Honda engineers are far from stupid people.
RE: Twin Charging a Honda CRX
Regards
Pat
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RE: Twin Charging a Honda CRX
RE: Twin Charging a Honda CRX
After that, I then started looking around for another off beat challenge, and VNT technology sounded really exciting, so I had a go at that.
After eighteen months of totally wasted money and effort I gave it up, and bolted on a simple ball bearing turbo, which was far superior to the VNT in every single respect.
Everyone from Joe the Saturday night street racer, to massively funded serious professional R&D outfits like Honda and Garrett have had a go, and given up on it too.
Twincharging has the advantages of both supercharging and turbocharging, without the disadvantages of either.
It is a lot of work, but fairly straightforward and easy to set up, understand, and get going to perfection.
Over all these years I have never known anyone that started a twincharge project to either give up on it, or be less than totally ecstatic with the final results.
RE: Twin Charging a Honda CRX
Regards
Pat
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RE: Twin Charging a Honda CRX
RE: Twin Charging a Honda CRX
But it is a far more robust blower. They do look larger, and that may be a problem.
If driven at about crank speed, it will work fine, have plenty of top end airflow, and it will last forever.
If it is going to be mounted directly over the inlet ports without subsequent intercooling, it makes more sense to use a larger displacement blower that will add minimal extra heat and not be really struggling with volumetric efficiency at very high rotor rpm.
If a blower is remote mounted, with plenty of intercooling after the blower, you can use a smaller blower and push it much harder.
For example, the Americans commonly use 6/71 GM blowers with displacements of 411 CID per revolution on small block engines. That may look grossly excessive, but in practice it has proved to work well.
An M62 would probably be quite adequate, but M90s are far more readily available at sensible prices.
RE: Twin Charging a Honda CRX
Find me an M62 for less than A$500 in Sydney, that I can borrow until I fit it up and I will certainly use the slightly more compact design.
I went to Eatons site and the critical size difference was any a few mm bigger. Length is not critical. It is housing width and depth (depending on orientation of mounting) that matters.
This will depend largely on whether or not I can flip the drive snout, gear box and rotors over 180 deg to reverse rotation
Regards
Pat
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RE: Twin Charging a Honda CRX
The rotors cannot be flipped over in the housing, as the output is triangular to prevent backfeed through the blower.
My M62 is in the bottom box of a large pile of VW parts, else I'd see how modular the design really is. (It is ex-Buick 3800)
RE: Twin Charging a Honda CRX
They where both for the SOHC d series. Mine is DOHC D series with moderately different manifold flanges.
What there is of the Endyne kit is much better design but virtually unobtainable. The Jackson kits while complete are easy to get but really are pretty much junk.
I agree that Jackson and Endyne probably just flipped over the drive, but I need to confirm that can be easily done without need to make patterns or one off billet parts
Regards
Pat
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RE: Twin Charging a Honda CRX
I agree the root cause of the vanes jammming is the deposits, but did not consider that the gasoline deposits would be much more different than the diesel ones. I now work with the diesel engines and we use a cleaning cycle to rid the 'sweep' of the vanes and the control ring of soot buildup after the engine is switched off and everything is hot.
In operation, once the layer has built up, the only thing to clean it off is the action of the vanes. Because the gasoline ex temps are higher, the vanes/control ring are more prone to this effect due to the vanes expanding more than diesel. The vanes get stuck at one end of the ring travel, as they climb up the thicker part of the deposits. There does not seem to me to be a way around this for relaible production VNT on SI.
Can I ask, how did you control the VNT vanes in your application? It is very interesting.. Was it purely mechanical i.e. throttle pulls vanes closed and then boost opens them again?
By the way, was the Porsche turbo vane-ring style VNT or just nozzle/throat style?
I would also like to just say that I am greatful for your opinion on these things, and that I am also a twincharge convert
RE: Twin Charging a Honda CRX
At the time (2001) it was the very first and only VNT turbo available in Australia.
This also used a vacuum actuator to operate the vanes.
That baffled me, and still does. Where on an un-throttled diesel does the vacuum come from to operate the vane control ?
The very first thing I did was toss the original Garrett vacuum actuator and fabricate own actuator from scratch.
This slowly evolved over about eighteen months of messing about, but ended up having two diaphragms one behind the other, on the same axis to control the vane lever.
After all these years the exact details escape me right at this moment.
But the basic idea was that a vacuum diaphragm was directly connected to the vane actuating push rod. A light spring forced the vanes totally closed, and the vanes were opened by manifold vacuum. This is exactly opposite to the original Garrett actuator.
At engine idle and very light throttle, the vanes were wide open. As you opened the throttle and manifold vacuum reduced, (for acceleration) the vanes would close. Full throttle gave fully closed vanes.
Now there was a second pressure diaphragm and spring arranged to operate from boost pressure. This was not rigidly connected to the actuation rod, but could push on the end of the actuation rod to open the vanes at full boost pressure.
So the vanes open under vacuum, close at full throttle, and open again at full boost. The control system itself worked reasonably well, but the engine was never happy with the extreme exhaust back pressures created.
It sounds great, slam the vanes shut at 1500 rpm and watch the boost pressure quickly rise, but that boost was nothing compared to the 80+ psi exhaust back pressures that mode of operation created.
The effect when you floored it was the engine would die completely for about two seconds, then there was a MASSIVE surge of acceleration.
At the top end, forcing all the exhaust through a very small turbine again caused huge back pressure, and very disappointing power.
It really needed a wastegate, but that was something I never got around to trying. The whole complex mess had horrible drivability, but I never had any vane jamming problems - ever.
It was all a huge step backwards from twincharging.
Whereas twincharging was successful beyond my wildest hopes, the variable vane VNT turbo installation on the same engine was truly awful in every single respect.
RE: Twin Charging a Honda CRX
I found that the range of vane operation is critical, and using the end-stop of the vane control ring lever to tune max exh bp and transient response must be completed before any other setpoints. There was no way that I could have ever closed the vanes to the maximum point. If I did ever go too far on the bp and snap the vanes open (i.e. max bp), I had similar symptoms - a combustion instability followed by a runaway boost condition and eventually misfire stall. The key was in fast transient control, and using the wastegate for safety.
The gasoline engine needs fast airmass control as the lambda operating range is much narrower than the diesel...
May I ask which engine you used the 3.0 VGT on?
The vacuum on the diesel engines is taken from the vacuum pump. They all have this to power the brake booster. The vacuum is controlled by a PWM solenoid, which goes high duty to increase vacuum to give a high exh bp condition. This has the benefit of a fail-safe system.
RE: Twin Charging a Honda CRX
Where you set that closed vane travel limit is critical, but I could never discover a setting that the engine was entirely happy with. If you don't close the vanes sufficiently, you lose all the supposed advantages of VNT technology. If you DO try to close up the vanes, the exhaust back pressure climbs to values that create huge exhaust reversion and massive exhaust pumping losses.
The engine I had this fitted to was a Mazda B6T, 1.6 litres, four valves, the DOHC factory turbo engine. The VNT turbo came from a three litre diesel with a rated power of 150Kw, which was my fairly modest power goal on gasoline.
RE: Twin Charging a Honda CRX
RE: Twin Charging a Honda CRX
And that corresponds to maximum tangential exhaust velocity coming out of the vanes.
A smaller a/r or vanes closed up will always produce more boost, unfortunately it also dramatically increases turbine back pressure.
Vanes wide open might give 5psi Boost, and 5psi back pressure.
Vanes closed might give 15psi boost and 80psi back pressure.
Closing the vanes just to get a higher boost reading, especially at low rpm, does not make the engine happier.
You simply cannot get something for nothing.
If the exhaust mass flow is minimal, trying to force it all through a pin hole just to rev up the exhaust turbine, only produces unacceptably high back pressure.