Quote:
Originally Posted by hobieboy
I thought I knew but now I can't explain it...
2 turbos, same boost. One big, one smaller. Why would a bigger turbo make more hp if both can hold same boost and same RPM?

If you look at the ideal gas law this might explain the issue. I think it is about heat added through the turbocharger.
Please excuse me, as I haven't studied this stuff in a long time. I finished engineering school in 1994 and don't practice.
However, from the idea gas law.... pV = nRT .
where.....
T = absolute temperature
n = relates to number of molecules of air.
V = we can consider the engine a fixed volume at a snapshot in time and rpm (even though this changes relative to volumetric efficiency, cam timing, lift, etc),
p= pressure
R = ideal bas constant.
We would agree that the more air / gas mixture at the appropriate ratio which you can burn, the more HorsePower (HP).
so.....
n = pV/RT. If R and V are constants and then R & V drop out leaving a constant ratio between n and p / T
n ~ p / T
since n has direct relationship to HP (more air burned correlates to more HP)
then we reduce this to HP ~ P/T.
conclusion: if absolute temperature were higher then HP would drop. Conversely if pressure increases, temp is fixed, HP goes up.
A drop in temperature of 20 F degrees to 150 F from 170 F is about 11 degrees on the absolute scale. 338.5 K from 349.6 K, which equates to 3.0% more molecules of air to burn.