Maybe some calculations will help some of you decide what size to get

------------

To determine how much air your engine can consume at peak rpm complete this simple formula-
CFM = (rpm x displacement x VE) /3456

rpm=max rpm you will shift at (6700 for example)
displacement= cubic inches of your engine (350 for example)
VE= Volumetric Effeciency (90% = .9, 104% = 1.04)
So a 383 that shifted at 6800rpms with a VE of 100% would consume 753cfm.
CFM = (6800 x 383 x 1) /3456

------------

Now carbs and throttle bodies are flow rated at a pressure drop of 1.5" Hg, you need to convert this to 1" Hg. So use this formula-

sq root (new pressure drop / old pressure drop) x flow at original pressure drop

So a 58mm TB that is rated at 1050cfm would flow 857cfm actually.
sq root (1.0/1.5) x 1050 = 857cfm

------------

So you can see for the mentioned 383 a 58mm TB would be enough for it. Try your combo out...

 

Thanks for the info, Ken.
Any idea what the typical 52 mm flows?
How about a 48. 550 if I remember correctly?

 

IIRC a 48 does flow around 550. I think each mfrs flow a little difrent for example AS&M lists this-
54mm flows 900 CFM
58mm flows 1050 CFM
Mono-Blade flows 1300 CFM

But i think i recall my BBK 58mm flowing 1000cfm. Either way its almost the same.

 

TTT for anyone else who's interested.

 

thanks!

 

i want the as&m monoblade(1350cfm) too much air cant hurt it right.lol

 

That means my 52mm that I've got will probably be just right for my little ol' 355.

 

How do you know the VE of your engine? Is it just typically 100%?

 

Typically close to 100% but you can use a tool like datamaster to know for sure.

 

Now how do you figure forced induction into this?

 

Volumetric Efficiency:

http://www.epi-eng.com/ET-VolEff.htm

Basically, how close to the max amount of air you actually induce into the engine.

 

Pretty cool.

 

Good stuff Ken. I'll add that to the big blue book O' formulas.

 

hmmm, that's very interesting. Buy my personal engineers calculations, looks like I'm just about right , well, I gotta a little extra "flow" their i probably don't need just yet.

 

Seriously guys, what size(s) are necessary for forced induction cars?