Maurice

I have been checking out a few carburators lately and have seen some sizing web pages ( http://www.smokemup.com/utilities/calc/airflow.cfm ). It says I should be running around a 600 cfm carb on my setup. Why did the Vettes come stock with a 750 cfm carb if all it needed was a 600 cfm? How may folks on here run the 600 vs the 750 on the 350ci engines? Is it really just overkill or is it helpfull to have a larger than needed carb or are the sites just wrong? Just trying to figure out what I really need vs what everyone else has and has just been accepted as the norm for what we "need". Thanks for your inputs.

The Dude

Economics, basically.

Back in the day Chevy was making all sorts of engines with all sorts of displacements and CFM requirements. With apologies to Lars and the other Q-Jet fans who read this, The Q-Jet is a very good "generic" carb that will work fine on everything from the most mild V8 to the most wild with just a jet/metering rod change.

It's small primaries and vacuum secondaries are part and parcel of that, also. Little bitty primaries provide good economy and snappy throttle response at low RPMS. And the huge, vacuum secondaries--which only open enough and flow enough to satisfy engine demand--can feed anything from a 305 to a 454 with a minimum of fuss and part numbers to keep track of on the various assembly lines.

Ganey

The formulas are really for single plane intakes. A 2 plane can run more.

You need to give your cam specs. to determine what you need.

Maurice

I have the edelbrock performer rpm cam #7102

Copied from the edelbrock web page......
Duration at .006 Lift: Intake 308° Exhaust 318° Centerlines
Duration at .050 Lift: Intake 234° Exhaust 244° Lobe Separation: 112°
Lift at cam: Intake .325 Exhaust .340 Intake Centerline: 107°
Lift at valve: Intake .488 Exhaust .510
Timing at .050 lift: Open Close
Intake 10° BTDC 44° ABDC
Exhaust 59° BBDC 5° ATDC

Maurice

So is it better to correctly "size" the carburator for you specific application or just stick with a 750cfm. Let me rephrase, in my circumstance, would a tuned 600cfm outperform a tuned 750cfm carb on a 350, or if they were both "tuned" there would be no difference in perfomance on a 350. Thanks for the reply.

Ganey

Run a 750. Yes, it is best to properly size, depends on several things incl. intake. No, 600 is too small on your setup.