Dave951

RPHarris Lets put up some real maps then. Are you trying to ask which is better, being at the dot on the first map (a turbo which has a lower max efficiency) or the dot on the second map (a turbo which has a higher max efficiency)? Taking a theoretical flow of 20 lb/min and a pressure ratio of 1.8. (Point marked by the red dot).

Granted this is just one point in the plot, but I'm just trying to see if this is what you were referring to.





From what I understand the relative efficiency of each turbo should be able to be compared directly. Thus then you would want to choose the turbo in which the majority of your curve falls into the highest efficiency % possible.

RPHARRIS

Oh god, it's all coming back to me now. It's an adiabatic process so you can't just use the ideal gas law...

y=(Cp/Cv)= (heat capacity ratio for a monatomic gas ...air isn't monatomic so this is approximate)

(P1/P2)(V1^y) = V2^y Solve for V2 (reversible adiabatic process)

T2= (P2V2)/nR Plug in V2 to find T2 (Ideal Gas Law)

HAVE FUN!!

RPHARRIS

Dave, that's exactly what I meant! Is 73% on one map the same as 73% on another regardless of its position relative to other lines/islands?

Dave951

RPHarris Yes, they can be compared directly. The efficiency tells us how much of the power (that the turbine from the exhaust side is delivering) that it put into the compressor is used to produce air pressure; the left over % is used to create heat. Since heat is a pretty big enemy to engines, we want to do everything possible to minimize the amount created, thus selecting the most efficient compressor.

blown 944

bob yes they are the same

The comparison is between inlet temp and density vs outlet at various pressure ratios and what turbine speed is required to make the given PR

Having the majority of your flow map across the highest efficiency means you will have the most dense air at that PR

This is why I like Holsets so much