[s-cars] Math quiz: turbo compressor choices

[Djdawson2 at aol.com]

OK... choosing a cold side for a 2.2...

Here's what I think I know:
2.2 liters, max 7000rpm, pressure ratio is 2.7, efficiency guessed at 85%.  
Based on these factors, it looks like these engines could require up to 
47lbs/min of air.  Reviewing the RS2 compressor map, it appears as if that turbo is 
maxed out at around 33lbs/min of flow.  If this is correct, I guess it's really 
obvious why my engine power peaks at just shy of 5k rpm.... that's where it 
would require 33lbs/min.  After that engine speed, boost drops off, as does 
power, simply because the compressor can provide no more air.

I've looked over the Garrett options.  I've made the following assumptions:
Efficiency is 85%
2.2 liters
7000rpm max
25psi boost at sea level for a PR of 2.7
47lbs/min is the max required air volume for this engine at 2.7PR.

Reviewing the maps on the various Garrett choices, this is what stands out 
for me:

"Super T04E-50" looks pretty good.  Full boost (25psi) capabilities at just 
shy of 3000rpm with no surge problems.  Max flow of 47lbs/min is possible, but 
efficiency is around 60%.

"Super T04E-54" looks like an OK choice, but not as good as the 50 trim.  
Full boost at engine speeds below 3700rpm should have surge issues.  Max flow is 
a bit short at 45lbs/min, and efficiency throughout looks worse than the 50 
trim.

"Super T04E-57" is interesting.  Full boost at engines speeds below 4000rpm 
should have surge issues.  Max flow is great at 49lbs/min, and efficiency is 
high up to 7000rpm... always 65% or better.  Looks like a good high end power 
choice.

"Super T04E-60" is also interesting.  It can support full boost down to 
3400rpm without surge.  Max flow is 50lbs/min, and efficiency is about 62% at max 
rpm, but doesn't look as good throughout the range as the 50 or the 57.

Those are my observations.  Any input, corrections, other factors I should 
consider... whatever, is welcome and appreciated.
Thanks,
Dave in CO