von

Need to know...I should be able to use 650cfm of air with my new streetported engine.

But whats the CFM of a stock or ported and polished TB S5 ? For comparing purposes.

NZConvertible

"CFM" is a commonly misunderstood term. Any airflow measurement must be accompanied by the pressure at which it was measured or it's completely meaningless. Obviously the higher the air pressure the higher the flow.
Even if someone's gone to all the trouble to actually measure the flow through the TB (which I doubt), you'd need to measure it under exactly the same pressure conditions it would see when your engine's supposedly flowing 650CFM to be able to compare them.
FYI, an NA 13B with 100% volumetric efficiency would be flowing 369CFM of air at 8000rpm.

No7Yet

You sure about that figure, von? 650 CFM is about what I expect to be flowing making about 400 hp (well, in the neighborhood of 45 lb/min).

Nobody I know has ever thrown an FC TB on a flowbench, but it's got almost as much crossectional area as a new Z06 TB, so I wouldn't worry about it on an N/A.

Brandon

mazdaspeed7

650 cfm.....I would really like to see that...

von

Comon ametures im serious...www.racingbeat.com

Carbed aplications have thier carbs flowing 600cfm for a streetported engine. The bridgported ones are 650cfm BUT in my case my street port has more volume and timing than a J-Bridge on a 4 port. So wouldnt it seem realistic to go with 650 or 700 ?

I dont know anything about carb but if RB is wrong please let me know.

RJHoupt

I know someone who has the racing beat intake manifold(which I just ordered....I can't wait!!!!!) and a holley 600cfm 4brl right off the shelf from autozone. He also has a street port, header, flywheel and clutch. I don't know what times he runs or anything, but I will post times from mine when I get the carb on. I have a holley 650.

Randy

von

Thank you...Yeah I know someone local from the drags who has a 600cfm on a streetport he says that I have a sneeking suspicion is the same desing as mine that I call Godzilla Port. Anyways he bangs 12k rpms but still I dont know his times. I remember him saying somthing like high 8s in the 1/8 but dont take my word for it.

I just wonder how bad my 6port manifold is going to work with this ?

RJhoupt ? Is the autozone one cheaper ?

Evil Aviator

As NZConvertible posted, the CFM rating depends on the operating pressure.

American 4-barrel carburetors are usually measured at 1.5" Hg vacuum. Therefore, a "650cfm" carburetor is technically a 650cfm @ 1.5" Hg carburator. Since a carburetor's flow rate is directly related to its vacuum, the carburator will flow less with less vacuum, and more with more vacuum. The rotary engine will have less vacuum than a typical piston engine. This is why rotary engines that acutally flow 400cfm will use a "650cfm" carburetor.