would the 20g make more power or less at 8-10 psi.? being bigger and all? and would it take longer to spool.?? thanks

the 20G would make more power since it flows more air. To put things in comparison, a stock 14B turbo at 8psi wouldn't make nearly the same power that a T66 would make at 8psi.

96 Indy Red Dodge Avenger I4 5spd
225.7whp/227.2wtq @ 10psi, currently running 12-14psi.
HRC Stage III turbo setup
JE 8.8:1 pistons
Eagle rods
block bored .020" over
GReddy FMIC w/ custom piping
1G crushed BOV
SPEC Stage 3 clutch
2.5" DP, 2.5" high flow cat, 3" ERT catback w/ Magnaflow muffler and 3" tip.
much much more...

Its like the age old question
What weighs more?
Ton of bricks
or
Ton of feathers

well of coarse a ton is a ton.
So 8 psi is 8 psi however we have to take into account the actual volumetric efficiency.

8psi on 20g would be more efficent.

My answer is not science but im sure you get the point.

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It deals with the volumetric efficency... A 16g at 8psi will say produce 90 hp while a 20g at 8psi will produce 115... The 20g will flow more air at any equivelant psi than a 16g because it is larger

I think everyone is dancing around the correct answer, but not quite hitting it. The first thing is to separate the compressor from the turbine. If we only consider the compressor, then our only task is to supply the engine with a specific mass of oxygen. The engine will add the appropriate mass of fuel to combust and generate a specific amount of energy (we calculate power from that energy). We will assume that the "air" around any compressors we choose to compare will contain the same mass percent of oxygen relative to all of the other components of "air" (that includes moisture content). We will also assume that the engine will add the appropriate mass of fuel relative to the mass of air we feed it. We should also assume no interaction between the compressor and engine, besides the transfer of air for combustion. We, of course, assume that the engine displacement and RPM are constant for any comparisons. So, how do you define what mass of air you are feeding the engine with a compressor? With our assumptions above, all you need is temperature and pressure. 8 psi is only 8 psi if it is at the same temperature upon reaching the engine. So, a T25 compressor could allow an engine to generate the same power as a T66 compressor if the air reaching the engine was at the same pressure and temperature. Unfortunately, we are bound by certain mechanical limitations. The ideal gas law sets the minimum temperature rise that the air must undergo when its pressure is increased. Any temperature increase beyond that minimum can be related to the efficiency of the compressor. I haven't looked at the maps, but you'd probably find that a T25 compressor would heat the air more at 8 psi than a T66 compressor at 8 psi. At 15 and 20 psi, the difference would probably be dramatic. I mentioned earlier that we would separate the compressor from the turbine. It takes a certain amount of power to turn the compressor. That power is supplied by the turbine. The exhaust stream is the energy source for the turbine. There is efficiency here to. A turbine will need a certain exhaust pressure ratio to produce the needed power to turn the compressor wheel. One turbine could require a higher exhaust pressure ratio to achieve the same power output to the compressor wheel. Since one side of that pressure ratio is fixed (atmospheric pressure), the increased pressure exists in the exhaust manifold. This can negatively affect the operation of the engine and reduce engine power output. So, a bad turbine choice could offset the gains achieved by a good compressor choice (at many operating points). Both must be chosen with care in addition to the actual compressor and turbine housings. Choosing the options based on calculations and publicly available charts is nothing but a best guess. Shops with intelligent employees and lots of dyno time could make a better recommendation. Only a design engineer in that industry armed with piles of confidential test data could do an excellent job of matching a complete turbocharger to a specific engine. I've rambled and gotten off the subject a little. I have left out a lot of details, but I think I've chosen my words carefully enough to not say anything technically "wrong". I am certain others can add to this.

Corbin

'95 ESI-T
Now with more power and fewer leaks



Gimme fuel...Gimme fire...Gimme that which I desire

All I can add is that running a mitsubishi-ish turbo means you have extermely limited choices for turbine housings and basically makes that point moot

IMO the turbine deal is not really of much importance until you switch to a Garrett, because my god they have a lot of choices to choose from for not only ARs but wheels, trims, etc...

1995 Eagle Talon ESi

what about lag. is there more with the 20g?

Simply answered.. of course, but you could undersize the exhaust housing for a reduced top end, but faster spool up.

Ball bearings can get you the best of both worlds.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician