Calculating optimum CFM for rotaries

[RICE RACING]

Originally Posted by dr.occa

I've been going over some math in determining various carb options for the rotary motors. I'm very familiar with the tried and true IDAs (running one on my 12A), DCOEs & 44PHH (running a pair on my 4AG) and the 4 barrels: what I'm scratching my head about is do I use the cc displacement at the taxed 720° rotation or the actual full 1080° rotation in calculating optimum CFM?

Here are the answers for my 12A using both displacement numbers (in cubic inches):

((8000[rpm] x 140cc[rounded up from 139.866421]) / 3456) X .85 = 275.46CFM


((8000 x 210cc[rounded up from 209.7996322158]) / 3456) X .85 = 413.2CFM

Which should it be?

Thanks Cheebs (previous post).

This is how you do it.

Capacity (per rotor chamber in Liters) x 2 (number of rotors) x Ve (1.15 = 115%) x (rpm)
0.573 x 2 x 1.15 x 9000 = 11861.1 L/m
Liters to m^3 / 1000
11.861L/m = 418.867 CFM

So that is the bullshit maths after I consulted with Howard Coleman......

The VARIABLES are the Ve.
and RPM

A PP will do over 125% if done right and run up to 10,000rpm
A RICE RACING STREET PORT will do 115% Ve and up to 8,500rpm
Stock port will do around 100% Ve and up to 7,000rpm

ALL of this great variability means you have to rely on experienced c-u-n-t-s who have done allot of this to recommend a carb for you that they have trialed and worked out for you

Racing Beat did allot of this already for the shit house 'double pumpers'

IF you want to do it on your own go ahead just keep in mind the way holley rate the CFM is at a certain amount of pressure drop in the rating test.

Ask rotaryshack nice and I am sure he will accommodate you