Im trying to map out a Turbo for my 12A. I have the equations but they are for normal piston car. Which to get CFM you multiply CID x Rpm x VE. which i know 4 valves or higher is 90% or .90, 3 to 2 valves is 80% or .80 for VE.How would i do it for a rotor. They have no valves would you do it by how many ports. I want to be able to match up the correct turbo for my car. i want to be able to get in the middle of the sweet spot .i know how to get my HCAF and LCAF. The car has a fresh new rebuild pretty big street port. Stg 2 CM and Holley 600. I know i can do a 2nd get but i want to buy a new Turbo. Thank you i did search and found nothing.

 

Use this formula for rotary engines: Airflow CFM = ((CID * RPM * VE) / 1728)

The VE depends on a lot of factors, such as the intake type, engine porting, exhaust type, and even the turbocharger type. Also, VE varies with engine RPM. I'm going to guess that 90% will be close enough in your case, but hopefully somebody with 12A carb/turbo experience can chime in with a more accurate number.

Most modern compressor maps are in lbs/min @ 545degR and 28.4"HgAbs, so it is probably best to convert your CFM to lbs/min with this formula: CFM * 0.6915 = lbs/min.

The 12A is close enough to the 13B that you could probably just use a common 13B turbo and avoid the math.
http://fc3spro.com/TECH/MODS/TURBO/fullturbo.htm

 

Thank you very much.

 

I noted a typo in the forgoing equation. To avoid confusion, I believe the author's intended value is 0.06915# per standard ft^3. Whereas: CFM * 0.06915 = lbs/min

 

Oops, I did mistype that. Thanks!

 

Thank you very much.

 

its the same as a 4 stroke piston engine but dont do the divide by 2 part of the calculation. It still a bit different from piston engines for selecting turbine size tho isn't it? because of the rotaries high egts you can use a larger turbine or A/R