Figuring out cfm flow numbers for our 4g63's
 

How do you figure out the cfm flow numbers for our Evo engine?

I know how to figure out the flow for a na engine. But I am not sure how to compensate for the turbo and the additional flow it creates. Anyone know?

SC~

The December issue of Hot Rod magazine has an article about turbos and part of it touches on your question. I couldn't find it on their web site but it is definitely in the Dec. mag. The major variable is volumetric efficiency. At 100% cfm is a pure calculation based on displacement and rpm. They say assume at least 100% for a turbo motor. They are measuring air flow in pounds per minute, not cfm and have conversion factors, etc. Really good article and this is only part 1 of 3.

the air flow formula is

CDI * rpm * VE * .5
--------------------------
.... ....1728

to arrive at CDI take CC and divide by 16.4
VE is usually in the .9 (90%) range

that will give you naturally aspirated airflow in CFM

to arrive at a boosted CFM
multiply the NA air flow number by the pressure patio (PR)

PR= 14.5 + boost pressure (in psi)
-----------------------------------------
.... .... ...14.5

so a boost pressure of 14.5psi or one bar would have a pressure ratio of 2

have fun plugging away

aaron

edit: if you are trying to plot compressor maps you might need to convert your final number into lb/min.
to do so multiply by .0691

Thats some good info Dale/ Aaron. Thanks.

I'm going through this exercise to figure out what kind of intercooler is needed for our engines. I found a site that custom builds intercoolers...but they list the applications by air flow needs.

Plus I am building a Turbo Austin Mini at home right now. And I'll need to eventually get an intercooler for the 1.3L engine. And it has to be a custom built one due to the size constraints of the engine compartment.....

SC~

dont know if it is relevant but when i have done datalogging with my scanner, at full WOT i have seen around 29 t0 31 lb/min of air flow

that is about right,

just for chits and giggles...

What was your boost pressure and rpm at that reading.
we might be able to calculate a true VE number for this engine.

edit: I will also need your elevation above sea level.