OMG, I made it through all 24 pages... it took me a week at work - seriously, not a full time week, but 'when i have time week'.
some really good info here, but then again, there's some misrepresentation going on. Mind you might might be slightly off topic.
Particulary I want to comment on turbo sizing.
Everybody here seems to be talking about the compressor, and compressor maps, etc. Turbo is made of two parts compressor and turbine. they are conected by a common shaft therefore turbine is as important in making power as compressor being drive by that turbine. Nobody mentioned manifold design/type...
Exhaust housing size is mentioned in only 2 posts in the whle thread, while it is a very important factor.
Exhaust housing size, along with manifold sizing/design and exhaust system greatly affect power and responsiveness of the engin.
Assume good manifold deskign (tulbural, no sharp turns, equal length, full split pulse separation, with 2 wastegates) and ample exhaust system used.
The bigger the exhaust housing the less restrictive the exhaust gasses path, therefore greater power putput. That is aswell compounded by the fact that less restriction lowers EGT's therefore raises knock treshold.
it is common that oem turbo setups usually use smaller exhaust housing as that produces a quick throttle response making car feel more powerfull than it actually is...
ok, ok, where i'm getting at, with regards to pre turbo WI.
I'm saying that all thought I agree with the fact that preT injection will incerase flow of the compressor, i think the because air is dense, compressor is harder to turn therefore is turbine and that is more resistance to the engine.
And if your turbo is outside of efficency range, wi might incerase air flow, but chances are that your exhaust housing is maxed out in terms of flow therefore more air will not make much more power.
Many people here seem to confuse boost with power. power is a function of much much power is made in cylinders and how much is lost for running rngine (resistance of bearings, inertial losses on pistons which are constantly accelerating up and down, resistance of the exhaust gas flow. Generally speaking in a healty setup should produce nearly 200% of it's NA power at 1 bar of boost (i.e. 2 bat absolute pressure). and it's not exacly 100% per 1 bar, but as you incerase the boost you should see incerase in power. keep incerasing boost further and you will eventually get to the point of diminshing returns, where more boost doe not produce as much more power as at lower levels. so you work out a happy safe spot for you or look what can be changed to make that boost range more efficient... bigger exhaust housing, more efficient compressor, etc...
I guess what I'm saying is that with small oem setup type turbo your tuning abilities are limited because of the size of the turbo. and normally stock manifolds are cast and generally pretty bad design (see twin turbo supra stock manifold).
but with building efficient systems (low exhaust restrictions) great efficiency can be obtained. taking that idea to new level, there are some great benefits when we reac the point when boost pressure is higher than exhaust backpressure... then you can use wild cams on turbo motors, and that allows you to spool large turbos with small engine with great efficiency.... a example of bad way to do it is the 800hp skyline mentioned earlier in this thread which at 3 bar makes less power than at 2 bar. too small compressors ? possily. exhaust restrictions must be huge. pumping more air will not solve the problem. get exhaust housings 2-4 sizes larger and it will make 900 on the same boost... they will spool a bit later tho...
I think water (and other pre turbo injection) has it's place and should be further researched. But results may vary in every case. It seems like ideal candidate would be turbos with smallish compressor but large turbine... where compressor is limiting factor of the system... cooling charge air by convection (evaporatino of water or other fluid) is a way to go i think, but needs more experimentation...
I was thinking... maybe along with spraying large quantities of methanol, inject pure oxygen to the intake tract... yes, it might be expensive but power gains might be great too.... would work good on drag cars...
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