Twincharging Cut Off?

[ynhrgt]

Not so sound idiotic, but couldn't I just copy this...

I really could use a diagram if you could draw one up.

Edited March 1, 2006 by ynhrgt

[PHATR32]

i knew someone ws gonna stick that pic up.

take a close look at it!!

also, do you really think itll fit in the engine bay?

steve

[discopotato03]

Hm , still need convincing I think . Before I start I want it fully understood that I don't want to be involved in any wars of any kind . I am willing to learn from anyone and at worst agree to differ over conflicting views .

Both blowers and turbochargers have their place and if one suited my purpose better than the other I'd use it . They both have good and bad characteristics so choosing the least worst is the go .

I have a better grounding with turbos but having said that have used roots blowers on large (645 Cu In per cyl V16) two stroke diesels . I could go into the whys and wherefores of later versions with basically a mechanically driven via a free wheel turbo that becomes exhaust driven at approx half revs . That version makes 3300 BHP compared to 2000 for the blower version and the last revision did 3500 from the same capacity .

Two stroke diesels are a long way from a four stroke petrol engine so they like different characteristics with forced induction . With car engines the best way to make early torque from limited capacity (without chemical supercharging ie NOs) is a blower of some kind because it can develop higher than atmospheric manifold pressure at low crank speed . Low engine speed torque is good but its not free horsepower because the power you get is after the parasitic losses of driving the blower . Its debatable how much manifold pressure is usable at low revs before detonation sets in ie wide open throttle meaning near maximum dynamic compression plus boost pressure .

The way I see it blowers will always have a pumping efficiency problem because of the high surface contact area around the screws/lobe rotors and the casing itself which will be anything but cool in an engine bay . Turbos will also suffer from this but their thermal mass would be less so less heat to conduct to the air particularly at high flow rates . Thats interesting what you say about screw blowers at 70% efficiency as I've not seen that before .

Turbos use rotary compressors and these are also not perfect because they will have an island of peak efficiency . In a perfect world this flow rate and pressure would coincide with the engines torque peak to give the coolest charge temps at that point .

I would say that the greatest advantage the turbocharger has is its ability to recover something from the waste heat that is ejected from the exhaust . This is also not a free ride though it is a valid attemp to recover waste heat that the fuel was burnt to develop .

Turbochargers have developed to the stage where it is not as hard as some think to get higher inlet manifold pressure than exhaust manifold pressure . The turbine and compressor combine to form the rotating group and its no exageration to claim the innertial weight loss through higher spec steel and aluminium alloys with thinner section blades in smaller diametres spun at dizzy revs can approach 50% of the old dinosaurs of the late 60's early 70's . Annular contact ball bearings have made a huge difference to the transient response of the rotating group compared to the high oil shear high contact area of floating bushes and plate / collar thrust bearings . What this ultimately means is that less exhaust gass energy read less restrictive turbines and housings are needed to make adequate shaft power with which to drive the compressor . Constant development is going into the science of gas turbines to seek more of the above efficiencies in order to lessen the energy requirement to drive them .

To make an exhaust driven compressor work all of the exhaust gas must pass through the turbine/s . For the exhaust gas to have any energy it has to be hot ie expanding so turbines and housings are going to be hot . A turbine housings job is to collect the gasses and accelerate them into the turbine inducer blades via its nossle . The more efficient the housing and turbine combination is the less restriction it will cause .

Turbocharging manufacturers style does not suit most of us because the compromises the manufacturer built in are not what we would given a choise . Legislation prevents them using exhausts and state of tune that promotes (to different degrees) what we want . They have to make what is economic green and socially acceptable to Mr Mrs and Miss - bad press means bad sales and economic suicide .

So in order to get the prefered pressure balance across the engine we need to size the turbo so that it can make the best use of the available exhaust energy . The turbine generally needs to be somewhere near the same diametre at the compressor and its trim and housings a/r optomised to power the compressor efficiently . The compressor (just like the turbine) has to be optomised in diametre trim style and speed range to compliment the turbine . The following example is going to nark some of you and I truly wish I could remember where I saw it so you could see the results for yourselves . The engine was a ... wait for it... SR20DET , the turbo was a HKS GT3037 in 52T wearing a .73 a/r turbine housing . The housing was extrude honed - smoothed - , the cams were from Jim Wolf Technology , the exhaust mnifold was a long leged stainless thing with I think a merged collector . External gate was I think a 40mm Tial . The Garrett production engineer who had a hand in it said that on the dyno it was in crossover up to ~ 52-5400 rpm . I can't remember what else was done to it though a highly developed Nissan ECU , injectors , pumps and IC

for sure . I think it had the early high port head with lots of time put into it .

Now for me I want 3.1 litres of RB 6 because the capacity and CR should make the torque I want without boost most of the time . If I get the turbo right its exhaust side should have very little restriction if any off boost so no issues here . The increased airflow from the compressor should be easily generated because I hope to use a reasonably small trim (for a GT40 compressor) so that the turbine gets an easy time and its transients should be snappy . If it breathes well it should inhale loads of air without high boost pressure so the turbo should not be working very hard so again low turbine inlet pressure .

If I thought I could use a blower of some kind that could do all this and plumb into an R32 bay , be efficient over a wide range of airflow rates and pressures and be quiet (engine exhaust and blower) and be tunable to fix any problems I'd probably do it .

Cheers A .

[StockyMcStock]

nice spiel, but everything still comes back to compromise. turbochargers and superchargers are both compromises in some manner, it all depends on what you want from your engine, and how you want it to behave.

If I thought I could use a blower of some kind that could do all this and plumb into an R32 bay , be efficient over a wide range of airflow rates and pressures and be quiet (engine exhaust and blower) and be tunable to fix any problems I'd probably do it

well i'll show you how to do it, then you can give it a try

seriously, it's hard but not impossible, and after seeing tony's results with the little 1.6L laser engine, i couldn't help but give it a try with an RB30DE. for me, the cost of an Opcon blower was too high, so i went with the twincharge. i may sell it all and try the blower out later on, but for now i want to see just how far i can push an eaton M90 with a GT40 together. packaging is the fun part......

ynhrgt: RE: that pic of the 26 up there. it's either a photoshop, missing parts or just a silly show demo thing. if you can figure out why it wouldn't work, then you are well on your way to understanding the twincharge system.

[ynhrgt]

Again guys, I appreciate the debate in turbocharging / supercharging.. but this isn't "WHICH" is better, it is how do I make the engine better with BOTH.

BTW, Warpspeed, I take back my whole "I don't get it" statement. I understand everything a lot better, I just had to draw a few pictures, and make a few obscene hand gestures regarding throttle position in proportion to poppet valve position. Basically, I understand now.

I have a few things I need to clarify still. How certain are you that at under FULL accelleration, with the bypass valve fully closed.. that the supercharger wouldn't suck up some horsepower? I mean its still connected to the drivebelt isn't it? Or would the turbochargers behind the supercharger push the supercharger to avoid the power loss?

I understand that under partial / light throttle or when the throttle is fully closed (fully stopped or when up-shifting) that ALL the air would be re-directed back into the supercharger inlet which is great since it uses its own energy to propel itself. But when you downshift what is the gaurantee that the bypass valve will re-direct everything properly espescially under high rpm since it has two turbos spinning behind it?

All I need is just a drawing of the piping if you could provide this So I have a rough idea to go by.

BTW is it a good idea to ceramic coat the turbos, turbo manifold and intake piping?

[StockyMcStock]

the blower does draw power, just in a different fashion to the way turbos do. we're not saying that it doesn't, cause it sure does! it will draw more power than usual too, as it's working harder than if it were drawing in merely atmospheric pressure air.

i'm not sure what you're getting at with the downshifting thing, just think of the bypass as releasing pressure from the piping when it's not needed.

i'm not going to draw you a picture. turbo pulls in air, pushes this into the blower INLET. the blower OUTLET then feeds through your intercooler, with the bypass gate situated somewhere along the line here. then it goes into the engine.

why are you set on using two turbos? wank factor? there is honestly no point at all to it. a single large turbo will be easier to package and work just as well. i would point out that it may be almost impossible to package two turbos and a supercharger into a skyline engine bay, especially if you have a power steering pump and an air con compressor.

[ynhrgt]

I'm not set on using anything till I figure out what I need to do. There is no need to get hostile here, I'm just asking some legitimate questions.

My question is exactly where does the bypass valve air go to? back to the supercharger? So I'm assuming you would need another pipe re-routing all that air that needs to be rerouted back into the supercharger?

I can live without air conditioning, it's not that nesscessary, besides it should free up some HP anyways. Power steering however I refuse to live without. I'll have to find a way to mount everything up.

the blower does draw power, just in a different fashion to the way turbos do. we're not saying that it doesn't, cause it sure does! it will draw more power than usual too, as it's working harder than if it were drawing in merely atmospheric pressure air.

i'm not sure what you're getting at with the downshifting thing, just think of the bypass as releasing pressure from the piping when it's not needed.

i'm not going to draw you a picture. turbo pulls in air, pushes this into the blower INLET. the blower OUTLET then feeds through your intercooler, with the bypass gate situated somewhere along the line here. then it goes into the engine.

why are you set on using two turbos? wank factor? there is honestly no point at all to it. a single large turbo will be easier to package and work just as well. i would point out that it may be almost impossible to package two turbos and a supercharger into a skyline engine bay, especially if you have a power steering pump and an air con compressor.

[StockyMcStock]

sorry i wasn't being hostile, just wondering if you realised that twin turbos was going to basically be an impossibility, with packaging.

the bypass outlet can either air-vent (it's very loud though) or re-circulate. you could recirculate it back to the turbo-blower connecting pipe but you might get some huge compressor surge, and it would slow the turbine shaft speed down pretty sharply on gearchanges in much the same fashion as a normal turbo setup does with large pipework volumes.

the other option is to vent it back into the turbo INLET, which is fine and should quieten it all down a fair bit.

i had my SC-14 blower air vented, it was pushing fairly low air volumes but was extremely loud on gear changes! depends on how much you care about noise i guess.

[ynhrgt]

Well, okay.. I understand that much. But now your telling me a different story heh.

From what I've understood so far, the bypass valve needed to be re-circulated or vented to atmosphere to relieve excess pressure when the throttle is partially closed or fully closed. I was under the impression that the bypass valve would re-route all the boost generated by the supercharger/turbochargers BACK into the supercharger inlet when the throttle is closed.

Now your telling me the supercharger would get compressor surge when the throttle is closed during upshifts/downshifts? I mean.. isn't the whole point of re-circulating the air to get rid of a lot of the supercharger parasitic loss by having its own air power it?

I should have asked this from the beginning, could you show me YOUR setup?

Please tell me if the following would work? It's a *VERY* crude drawing.

sorry i wasn't being hostile, just wondering if you realised that twin turbos was going to basically be an impossibility, with packaging.

the bypass outlet can either air-vent (it's very loud though) or re-circulate. you could recirculate it back to the turbo-blower connecting pipe but you might get some huge compressor surge, and it would slow the turbine shaft speed down pretty sharply on gearchanges in much the same fashion as a normal turbo setup does with large pipework volumes.

the other option is to vent it back into the turbo INLET, which is fine and should quieten it all down a fair bit.

i had my SC-14 blower air vented, it was pushing fairly low air volumes but was extremely loud on gear changes! depends on how much you care about noise i guess.

Edited March 1, 2006 by ynhrgt

[StockyMcStock]

if you re-circulate the bypass back into the supercharger-turbo connecting pipe, when you change gears at full noise you'll get massive air flow through the pipe, at high pressures, which relieves the pressure on the blower nicely. however, all this air then hits the turbo compressor wheels, in much the same fashion as in a conventional turbo setup. tony had it like this, and couldn't hear them surging, but technically it would be better to air vent it or re-circulate it back into the turbo INLETS.

your picture is correct, that is how mine is set up, and tony's was too, except we just use a single large turbo. sorry i don't have any pics of it, it's not fully complete yet. i'm currently re-fabricating my manifold to a low-mount so that the blower can physically fit in the engine bay. there are a lot of packaging problems, trust me!

[ynhrgt]

Well, I'm assuming I can't use a regular re-circulating blow off valve at all? No PTSHHH sound hahaha. Lol.

By the way, could you explain to me again why the supercharger WOULDN'T hold back the turbocharger? I mean at higher rpm, wouldn't the supercharger lose its charm? I couldn't find a clear explanation why again

I'm not sure how would I stretch a pipe across the engine back BACK into the turbocharger inlet pipes, wouldn't it be just better to recirculate that air back into the connecting pipes? What is the benefit of rerouting into the TURBO inlet pipes?. that would take a lot of damn piping work lol. Could you offer a simple suggestion using my picture as a guide?

if you re-circulate the bypass back into the supercharger-turbo connecting pipe, when you change gears at full noise you'll get massive air flow through the pipe, at high pressures, which relieves the pressure on the blower nicely. however, all this air then hits the turbo compressor wheels, in much the same fashion as in a conventional turbo setup. tony had it like this, and couldn't hear them surging, but technically it would be better to air vent it or re-circulate it back into the turbo INLETS.

your picture is correct, that is how mine is set up, and tony's was too, except we just use a single large turbo. sorry i don't have any pics of it, it's not fully complete yet. i'm currently re-fabricating my manifold to a low-mount so that the blower can physically fit in the engine bay. there are a lot of packaging problems, trust me!

[StockyMcStock]

the supercharging is just a mechanical air pump. it takes in a fixed gulp of air, then pushes it out the other side of the casing. do it fast enough, and you get a pressure increase across the thing.

now if you push more air into it by increasing the pressure at the inlet, it just passes that amount of air out the other side, same as before. except there's more of it. same as if you ran it at 50,000 feet above sea level where the air is less dense, it'd push less air out the other side. all you're doing is pushing more air into the same gulp that the blower takes.

read my post again, you even quoted my explanation of why you should re-circ the vent back into the turbo inlets rather than the turbo-blower connecting pipe.

[Cubes]

What charger is it you are using StockyMcStock, I know you've said in the past. I've forgot.

My guess its still going to have the turbo feel to it, just a turbo on a big cubed motor.

[StockyMcStock]

i've got an Eaton M90, same as used on the supercharged 3.8 commonwhores here in aus. mine came from the US though, and is newer. there were a whole bunch of revisions to the design over the years, mine is one of the more recent models.

My guess its still going to have the turbo feel to it, just a turbo on a big cubed motor.

you're pretty much right there. i would expect it to feel a lot like a twin turbo big block V8, with very well sized turbos. stonking low-end pull, then it just takes off when the turbo comes on song.

tony and i went to a lot of trouble picking the exact turbine to use, and i hope to see turbo boost well below 2500rpm. time will tell how good our estimates were though.

god, i starting making the manifold today. what an abortion of a thing! you won't believe the lengths i had to go to with header routing to make it all fit.......

[ynhrgt]

Yeah, I was just wondering if the supercharger wouldn't be able to keep up with the turbochargers outlet boost pressure. Which is a legitimate question imho, because at higher rpms espescially towards redline, superchargers run out of breath, exactly how sure are you this wouldn't impede on the turbochargers flow?

I mean the turbocharger has a greater highend, your comment sort of contradicts that saying a supercharger can maintain this flow even towards redline.

the supercharging is just a mechanical air pump. it takes in a fixed gulp of air, then pushes it out the other side of the casing. do it fast enough, and you get a pressure increase across the thing.

now if you push more air into it by increasing the pressure at the inlet, it just passes that amount of air out the other side, same as before. except there's more of it. same as if you ran it at 50,000 feet above sea level where the air is less dense, it'd push less air out the other side. all you're doing is pushing more air into the same gulp that the blower takes.

read my post again, you even quoted my explanation of why you should re-circ the vent back into the turbo inlets rather than the turbo-blower connecting pipe.

[Warpspeed]

For some strange reason, I have not been receiving e-mail notification of additions to this thread ??

Anyhow, I will attempt to explain why the supercharger can never be restrictive.

Any supercharger that is set up to make some positive boost, only does so because it pumps a larger volume of air than the engine would normally flow. The engine acts like a restriction to the supercharger, and the pressure builds up between the supercharger outlet, and the engine induction. This positive "boost" pressure will rise, until the flow rate through the supercharger and engine are exactly the same.

Because the supercharger and engine are directly coupled, they will rise and fall in speed together, and the boost pressure may vary slightly with Rpm, but the supercharger is never going to be a restriction to the engine while it is producing some positive boost pressure. So there is never the worry that a supercharger is going to become a restriction and limit engine power. It is there to do exactly the opposite.

By placing a turbo compressor ahead of the supercharger, nothing has really changed, except the supercharger now sees some already compressed air at it's inlet. It can still never be a restriction, the supercharger will always further increase the boost pressure coming out of the turbo to something higher.

Yes, the supercharger will absorb some power, and so will the turbo. But they give back far more power than they consume. In fact the supercharger will be pumping denser air, and the drive power is even higher than it would be if the intake was just open to atmospheric pressure. Believe me, none of that really matters.

Your piping diagram would work fine the way it is drawn, provided no airflow meters are being used ahead of where the wastegate is. The airflow meters need to measure exact engine airflow, and that cannot happen if you are venting some air that will never reach the engine.

Although just venting air from the wastegate will work, it would be very noisy whenever the wastegate is open, and that will be almost all of the time except at full throttle. Much better to feed the air back either directly into the turbo intake, or directly into the supercharger inlet, (after the turbo). It will vastly reduce the noise problem. It would also allow you to use an airfolw meter in the usual location before the turbo. That would work because all of the air going through the airflow meter also goes through the engine, no matter if the wastegate is bypassing air or not.

I fully agree with stocky that a single large turbo has many advantages in a twincharge application. Cost and packaging being the main ones. I have already done all of this myself, and had a twincharged system running on my car for over eighteen months. Stocky is in the final stages of getting his twincharge system on the road. Stocky having previously had a supercharged engine fitted with this bypass system, we both know and understand the requirements pretty well. I have experimented with all types of bypass systems and the wastegate idea works wonderfully well. If you fit a turbo blowoff valve the car will be a jerky pig to drive. Try it and see. The bypass has to be proportional, smooth, and progressive in action. A blowoff valve is sudden and violent.

Anyway once the whole system is fitted to the car, minor pipework changes and bypass systems changes are fairly easy to experiment with. The big drama is mounting and driving the supercharger, and locating the turbo and two wastegates around everything else in the engine compartment.

[ynhrgt]

Okay, I just have a few last questions.. which shouldn't be too hard to answer at all.

Which would be better? Rerouting the recirculated air back into the turbo/supercharger connecting pipe or back into the turbocharger inlet (which i'm assuming is directly after the air filter)?

Well, I'd really like to use a conventional blow off valve of some kind if possible, since I have a nice Turbo XS RFL bov sitting at home waiting to be used . I guess it would also be impossible to adapt a bov AND a wastegate into this correct? lol.

I will update my piping diagram soon. Your sure this bypass is the best I could possibly go with?

For some strange reason, I have not been receiving e-mail notification of additions to this thread ??

Anyhow, I will attempt to explain why the supercharger can never be restrictive.

Any supercharger that is set up to make some positive boost, only does so because it pumps a larger volume of air than the engine would normally flow. The engine acts like a restriction to the supercharger, and the pressure builds up between the supercharger outlet, and the engine induction. This positive "boost" pressure will rise, until the flow rate through the supercharger and engine are exactly the same.

Because the supercharger and engine are directly coupled, they will rise and fall in speed together, and the boost pressure may vary slightly with Rpm, but the supercharger is never going to be a restriction to the engine while it is producing some positive boost pressure. So there is never the worry that a supercharger is going to become a restriction and limit engine power. It is there to do exactly the opposite.

By placing a turbo compressor ahead of the supercharger, nothing has really changed, except the supercharger now sees some already compressed air at it's inlet. It can still never be a restriction, the supercharger will always further increase the boost pressure coming out of the turbo to something higher.

Yes, the supercharger will absorb some power, and so will the turbo. But they give back far more power than they consume. In fact the supercharger will be pumping denser air, and the drive power is even higher than it would be if the intake was just open to atmospheric pressure. Believe me, none of that really matters.

Your piping diagram would work fine the way it is drawn, provided no airflow meters are being used ahead of where the wastegate is. The airflow meters need to measure exact engine airflow, and that cannot happen if you are venting some air that will never reach the engine.

Although just venting air from the wastegate will work, it would be very noisy whenever the wastegate is open, and that will be almost all of the time except at full throttle. Much better to feed the air back either directly into the turbo intake, or directly into the supercharger inlet, (after the turbo). It will vastly reduce the noise problem. It would also allow you to use an airfolw meter in the usual location before the turbo. That would work because all of the air going through the airflow meter also goes through the engine, no matter if the wastegate is bypassing air or not.

I fully agree with stocky that a single large turbo has many advantages in a twincharge application. Cost and packaging being the main ones. I have already done all of this myself, and had a twincharged system running on my car for over eighteen months. Stocky is in the final stages of getting his twincharge system on the road. Stocky having previously had a supercharged engine fitted with this bypass system, we both know and understand the requirements pretty well. I have experimented with all types of bypass systems and the wastegate idea works wonderfully well. If you fit a turbo blowoff valve the car will be a jerky pig to drive. Try it and see. The bypass has to be proportional, smooth, and progressive in action. A blowoff valve is sudden and violent.

Anyway once the whole system is fitted to the car, minor pipework changes and bypass systems changes are fairly easy to experiment with. The big drama is mounting and driving the supercharger, and locating the turbo and two wastegates around everything else in the engine compartment.

[Warpspeed]

It probably does not matter much if the bypassed air goes back into the supercharger inlet, or the turbo inlet, as long as the air can circulate freely through the supercharger with a closed, or almost closed throttle.

Back to the turbo inlet has the advantage that it will eliminate any possibility of compressor surge, so that might be better. Just make sure that all that volume of recirculating air cannot cause any turbulence back at the airflow meter at small throttle openings, or the ECU may not be terribly happy.

After two years of testing and experimenting with many alternative bypass methods, I can only suggest that a modified wastegate works extremely well, and a modified turbo blowoff valve will give absolutely horrible drivability. But do it any way you want, it is your car. We can only advise you of the things we have found not to work, and perhaps save you from a few problems.

The same goes for engineering a good reliable belt drive for the supercharger. You can listen to the experiences of people that have already succeeded after having had some real dramas, or you can learn it all yourself from scratch the hard way.

[ynhrgt]

Can you recommend a good wastegate? I'd rather avoid tinkering around with wastegates since I'm not a pro. heh.

BTW, is it a good idea to ceramic coat the intake pipes, and the turbo/supercharger connecting pipe?

I'm planning on ceramic coating the turbochargers, turbo manifolds, and probably doing a real nice custom intake heh.

It probably does not matter much if the bypassed air goes back into the supercharger inlet, or the turbo inlet, as long as the air can circulate freely through the supercharger with a closed, or almost closed throttle.

Back to the turbo inlet has the advantage that it will eliminate any possibility of compressor surge, so that might be better. Just make sure that all that volume of recirculating air cannot cause any turbulence back at the airflow meter at small throttle openings, or the ECU may not be terribly happy.

After two years of testing and experimenting with many alternative bypass methods, I can only suggest that a modified wastegate works extremely well, and a modified turbo blowoff valve will give absolutely horrible drivability. But do it any way you want, it is your car. We can only advise you of the things we have found not to work, and perhaps save you from a few problems.

The same goes for engineering a good reliable belt drive for the supercharger. You can listen to the experiences of people that have already succeeded after having had some real dramas, or you can learn it all yourself from scratch the hard way.

[Warpspeed]

I very strongly suggest you get it all working and sorted out before spending big money on cosmetics. Once something is ceramic coated, it is not possible to cut and weld it, or modify it in any way.

Any external wastegate will work provided the control diaphragm is AT LEAST twice the diameter of the wastegate poppet valve. Garret, Teal, or Turbonetics wastegates are very good. The Chinese ones you need to be a bit careful.

Nothing you can buy will work straight off out of the box, you need to find a suitable much lighter wastegate spring. That will take a bit of experimentation to get it exactly how you want it.