Because you have a greater VE and better efficiency with the bigger turbo. It's not the CFM rating of the turbo, as the engine and VE dictates the CFM, not the turbo.

 

HTA3586! - This is my fav. turbo right now.

Michael

 

+1 for 600HP pump gas turbo

 

Might be agreeing in radically different ways, but the difference is Airflow independent of what you want to name it.

Air compressors are the same whether its the 30hp craftsman that runs the shop or the 2.5hp that you use on small stuff. Lbs/min is a measurement of air mass which can be converted to CFM and vice versa. It might be more accurate to say a 35R moves more lbs per min than a stocker, but it becomes semantics when in reality its still just air volume.

Engine VE is the amount of the total airflow that can be used by the motor, boost being what stacks up and cant be ingested. This can be because of turbine backpressure, pressure drop in the intercooler or before the turbo. Anything that allows the engine to breathe better will lower boost since VE has gone up.

Some manufacturers, BW being one, do rate their turbos in M^3/CFM.

 

What I am saying is that it doesn't matter how much a turbo can potentially flow at a certain psi. That doesn't matter. It matters what it's connected to, which is our engine. The engine is what dictates the maximum airflow.

The only reason a bigger turbo can sometimes (not always) produce higher horsepower numbers at the same psi as a smaller turbo is because of two things only...VE and efficiency (temp).

Volumetric airflow through an engine is:

A(cfm)=(Cid*VE*RPM/3456)PR

To convert to a mass airflow:

n (lbs/min) = P (psia) x V (CFM) x 29 / (10.73[ft3·psi· °R-1·lb-mol-1] x T)


You can see the only two variables when going to different turbos is the VE and the T. The T is reduced because of the bigger turbo being run in a higher efficiency island (usually the smaller turbo is being compared at a psi where it is maxing out or close to it, blowing hot air) and the the VE is increased because of the larger hotside and turbine wheel.

Just because a 35R can flow way more than a 16 at 23 psi, doesn't mean it will on our engine. Actually, when smaller turbos are run in their efficiency range, like a 50 trim at 15 psi or so...they can actually achieve more HP than a bigger turbo that is running in a lower efficiency range at that same boost. It's very uncommon to see this, but if the boost gets low enough and the difference in VE isn't too much, you can see it.

I really didn't mean to get into this discussion, but it's sort of a pet peeve of mine when someone says a bigger turbo can flow more air at the same psi as a smaller turbo, so that's why you get more HP. That just isn't true...it's the greater VE and reduced temps (higher efficiency) that achieve the higher HP. The comarison is just usually so skewed because we are usually comparing a completely maxed out small turbo and a big turbo that is right in the sweet spot.


Eric

 

Good numbers, E85 looks like a winner cant wait to convert.

 

nice #s