Twin charging

Hey all a friend is playing with the idea of twin charging his car. It already has a turbo and he wants to fit a very small supercharger (off one of those weird Japanese 600cc supercharged vans).

All the systems on cars I know of - Lancia Delta S4, March ST, new VW twincharge seem to rely on electronic trickery. We've researched how these cars do it but want a simpler, mechanical way of doing it using valves and stuff.

Are there any other cars that twincharge?

How would you go about twincharging, what DIY ways have been done?

We've got several of our own ideas already but what does the group reckon?

Reply to
fishman
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I would say it is a waste of time. Go for a ball bearing turbo to increase low down boost. Or increase displacement of the engine.

Fraser

Reply to
Fraser Johnston

It probably is a waste of time compared to what you suggest, but it's interesting and fun. I think it is a ball bearing turbo already. (GT28RS)

Reply to
fishman

How about referencing the boost from the turbo to operate a pressure switch, that will kick out a magnetic clutch like they use aircon compressors.

That way, when boost is off/low on the turbo, supercharger kicks in, boost climbs on the turbo, reaches level set on the hobes/pressure switch, turns off the mag clutch, supercharger goes into freewheel. Would that work, is it practical.

Reply to
NeedforSwede2

There's quite a lot of info in the interweb from people who have twincharged the supercharged Mk1 MR2. Some getting upto 450bhp from a 1.6 4AGE since they can use a huge turbo and have no lag. Here's a start

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I was doing it I'd get a electric clutch for the supercharger so that once the turbo is producing sufficient boost the supercharger can be disengaged. Once that's happened you need a valve to stop the turbo boost going back out the supercharger.

Reply to
Homer

You could hook up a supercharger as normal to run say 15psi if geared accordingly. You could then fit a big turbo that can only boost at high revs if no supercharger is fitted - this would give better top end power and no lag. The extra exhaust gas from the supercharger would allow the oversized turbo to boost early and "take over". The supercharger in effect would only do anything fron low revs, and it would fill in the lag only. Then the oversized turbo takes over early. It will make more power at a given boost level simply because the turbine and turbine housing are big, and not restrictive in the same way a standard (boosts from 3k) one is. The only proviso would be that you fit a large reed valve (like one from a big outboard two stroke) after the turbo before it feeds the plenum. If you dont the boost from the supercharger will all just escape at low revs, and its energy will be totally wasted.

Fueling should be easy. The standard turbo arrangement is a three port regulator that keeps the fuel pressure at "x" above manifold pressure. It ought to be ok, provided that the fuel pump can deliver enough fuel for the extra boost at high rpm against the extra pressure. You could need bigger injectors though.

But rather than go with all this mechanical mayhem, fit the same big turbo and hit it with a dose of nitrous to make it boost from 1k rpm??? Then use a pressure switch in the plenum once boost arrives to turn off the nitrous. This happens fast so a bottle lasts absolutely ages. This setup potentially gives better power too because you are not wasting energy turning a supercharger...

Reply to
Burgerman

And if you forget the clutch the valve isnt needed other than the one thats essential on the turbo outlet!

Reply to
Burgerman

I think you will find this wont work as you expect...

Reply to
Ed

I never tried it. But as far as I can see it should? Why do you think not?

Reply to
Burgerman

It's much better to feed the turbo into the supercharger, then out of the supercharger into the intake manifold (via intercooler) The supercharger then must have its own bypass valve, which many do although usually too small do, to regulate the boost of the supercharger, that also happens to open as the turbo starts to kick in, ultimately bypassing the supercharger.

Although this is very simplified, what you get is improved supercharger efficiency as its assisted early by the turbo, just as the supercharger also helps the turbo in the first place. What you must then allow is the bypass valve to open fully once the turbo is on boost, at this point you can disconnect the supercharger, as its not doing anything.

The trick is to stabilise the bypass valve so it doesn't get into a resonance with the boost fluctuations of the supercharger, this can in practice be actually quite hard and is one of the reasons why this system on my car seems so complex.

If your feeling even more adventurous you can also control the bypass valve so that at light throttle and idle conditions it is also open, thus allowing a free air path around the supercharger and improving off throttle economy :)

I speak from practical experience on all aspects of above..

Ed

Reply to
Ed

Then the supercharger is trying to draw all its air through a non spinning turbo at low rpm! And hindering off boost (turbo) performance. As well as hindering on boost performance. Because rather than increasing flow directly in to the motor as well as pressure you are running up against a fixed volume positive displacement pump!

You want to feed the output DIRECTLY into the engine so as you dont just compress it before the supercharger and heat it up. Because the turbo is not a positive displacement pump, you are simply limiting its flow, if its a big one, although not the pressure.Is this how yours is arranged???

then out of

Not seen a bypass valve on a supercharger. Only blow off! (You know metal plate, big springs) Only played with old sprintex, and some bike ones, and the big ones used on serious drag cars. (Wade?)

Seems that both ways would work. But that your way would inhibit flow until the bypass opens? It probably doesent make much difference either way, except. My way you are adding turbo air to an already boosted intake. OK it will be at a lower volume and pressure than the turbo is supplying but its a positive displacement. So there should be no need for any boost regulation or bypass. Engine gets more volume, so smaller compressor would be needed?

Either way it would be interesting to see what difference it would make!

Yes. What controls the bypass? My way wouldnt need or want one?

Economy was never one of my interests! But yes it should. But having to draw air through a non spinning turbo (intake restrictor) would reduce both power and economy due to pumping losses and lower airflow???

So again doing it my way would actually help here if you did keep a supercharger bypass?

Well I cant! I built a lot of serious stuff including one off turbo setups, superchargers, and turbo/nitrous stuff but it always seemed over complicated to go super/turbo to me!

Surely you could fit a truck T5 or something on yours rather than a exhaust restricting 2.5/3/etc? and gain huge top end advantage?

350bhp per litre is easy enough, just go rich, loadsa boost with big non restrictive turbo!
Reply to
Burgerman

Wrong, the turbo always spins faster than the flow needed even at low rpms, it just cannot create positive boost. Its never a restriction on the intake to the supercharger. If you were here I could demonstrate this in practice.

No, read what I said :) You have a bypass valve that when the turbo is on boost its bypassing the supercharger totally. So again that does not impose a restriction.

Check out the Lancia Delta S4 system, and if you can find it the Nissan March ST system. They are almost identical. Its not a fluke. Its simply the best way to do it.

How I have described is exactly how is the best way to do it. Also the supercharger does not generate much heat since when assisted by the turbo, its pressure ratio gets progressively smaller until its not need at all. That is WHY a supercharger and turbo can complement each other so well, just so few are capable of understanding this or making it work.

I'm most familiar with the Eaton type chargers. Not the most efficient but they offer good value for money. Its common on the larger Eaton ones to have a pretty similar arrangement as a turbo where an actuator opens under boost to recirc/bypass the supercharger.

Not so, since without the supercharger the turbo drops off anyway, as alone it cannot sustain its own boost. Again I could demonstrate this if you were here..

Perhaps this diagram I have will help:

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And for comparison the Lancia Delta S4 layout:

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Remove the intercooler after the turbo on the lancia and amazingly both systems have identical pipework - coincidence? :) I think not! Interestingly Lancia had real issues controlling the supercharger bypass (show as the left pipes on the supercharger)

Ed

Reply to
Ed

I doubt this, because without enough exhaust gas to spin it up I have seen big turbos stopped while the throttle is being blipped up to 2k revs. The way to find out would be to measure the pressure between compressor and super, accurately.

But since total air pressure is a function of the amount of compression it makes no difference if this comes from the turbo, the supercharger or a combination of the two. 2 bar is still 2 bar. You still get the same temperature in total. Plus that caused by the extra heat soak from the turbo etc. And the bypass has to be timed perfectly if it is to not cause a few probs during transition.

You dont need to I have been doing this with nitrous on drag bikes for 20 years! With the huge advantage of less available oxygen untul after ignition, and massive charge cooling doing the opposite to the supercharger. This allows greater boost as well before detonation once the nitrous is switched on.

With a bypass valve you have a bit of a transition problem because if you open it "late" so the turbo is properly self sustaining then its in the way for a time. If you open it early and its not generating enough power or boost alone it will drop off boost causing your bypass to close. This is the obvious achillies heel I would have thought. Doing it my way would not even need a bypass.

I know how to fix it though. Do both! Add another bypass with a reed valve from an rd 250 or some small bike past the supercharger as well. Now you could open the bypass later or not at all. That would allow your percieved low speed efficiency gain (which I still cannot see actually helping personally) to remain and allow your supercharger to run free and do nothing much at higher revs.

Reply to
Burgerman

Ok, if that was the case without a supercharger, as soon as you added one it would be a non issue..

Thats not right, since each have different efficiencies, and thus same pressure at different densities. The whole point of all of this is to get each working as efficient as possible. Roots chargers are in some cases horrendously inefficient, and so will be producing allot more heat for a given pressure ratio and flow volume than a turbo.

The bypass is not so much timed right, its pressure activated, but yes it must be damped and controlled in such a way that its smooth.

Yes! Quite, but there is no nitrous in the system were talking about.. :)

If your way is better do you have any suggestions as to why both examples I showed did not do it?

I need to show you a graph I have of the turbo helping the supercharger. Its quite interesting, Ill post it later if I can find it..

Ed

Reply to
Ed

I realize that but basically any theoretical gain is small and unlikely to be seen in practice.

Buggered if I know! Maybe it didnt occur to them!

Reply to
Burgerman

Upto 80% turbo compared to a roots supercharger of around 50% or so..

Hahahah!

Reply to
Ed

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