I plan to swap my 2bbl on my 69 307 to a 4bbl. Any ideas as to what size to go to? I have heard everything from a 390cfm to 600cfm. The car is a driver, basic engine.

My recomendation is a 600 vacuum secondaries. Good driveability and the carb is gonna feed gas thru the secondaries depending on engine demand.

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Our affair with Camaros is a live sentence without the possibility of parole. www.geocities.com/c68ss (http://www.geocities.com/c68ss) http://home.coqui.net/borench

agree

Would 650 cfm be to large or stay with a 600?

stay with a 600v2.....

ditto

I vote for a 500cfm edelbrock. If you do the calculation for a 307 if you spin it all the way to 5000, which is probably not gonna happen in my opinion it only requires 444cfm. Even if it spun up to 5500 it still only needs 488 cfm.
CID X Max RPM(this takes into account your cam size) / 3456 = CFM requirements

good luck,

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Jason Renschler
Gilbert, AZ
1968 Camaro - 350 4-speed
1969 Camaro - 350 4-speed

[This message has been edited by jrenschler (edited 07-12-2002).]

IMHO, I agree with most of the guys here. Bigger is not always better when you're talking carbs. It might take some searching, but Holley used to make a 550cfm spread bore, vacuum secondary, as a direct replacement for the Quadrajet. Just in case you don't know, spred bore means the primaries are real small & the secondaries were real large. Benefit, if you keep your foot out of it, you could get close to the same mileage as will the 2bbl. And for normal driving the small primaries will keep it much more streetable. Drawbacks, you either need to find a manifold or spacer set up to accomodate the different size inlets. Also, if at any point you just hammer the gas you will notice a distinct hesitation just before your head gets whipped backwards. So coming off the line takes some playing with the RPM's to make is smooth and if you're already rolling you need to ease into the throttle. Otherwise I thought this was a great combo on a '68 Chevelle 327 I owned that served as both a grocery getter & weekend racer.