which carb?

[bmrrwolfe]

I'm finally to the point of redoing the motor, its the original 307 and i plan on just doing all the gaskets, and putting an aluminum intake manifold and an edelbrock or holley carb and headers, but was told the 600 CFM would be to much for this motor? is this true? Also can someone explain an electric and manual choke and which one would be best (its gonna be a kinda daily driver but stored for winters)
This is the kit i was looking to get from summit and seems to be a great price!
http://store.summitracing.com/partde...4&autoview=sku
or
http://store.summitracing.com/partde...5&autoview=sku
Thanks!

[john02fxdl]

Even though it's gonna be a stock motor, the upgrade to alum. intake and 600 carb will be fine. Go with an electric choke, vacuum secondaries for fuel mileage and driveability. Electric choke is powered by an ignition hot source and heats a coil/spring on the side of the carb that slowly opens the choke. When the trucks off, the coil/spring on the side of the carb will cool(no electric going to it to heat) and automatically close the choke. A manual choke will require drilling a hole somewhere on the dash(if it wasn't equipped from the factory) so you can pull the knob in and out(choke open/ choke closed) to manally operate the choke. If you've never had any experience with a manual choke before, then absolutely opt for the electric choke.

[Wrenchbender Ret]

I agree with John but prefer the performer carb. If a guy can do his own carb work, the Roch. Q-jet is the best way to go, especially on a smaller engine like a 307.

[cparman]

you mean like this? 69 307, HEI, Edelbrock, 600 Holley w/electric choke. Runs perfect

[bmrrwolfe]

Originally Posted by cparman

you mean like this? 69 307, HEI, Edelbrock, 600 Holley w/electric choke. Runs perfect

Thats exactly what i plan to have mine like!
nice and simple, still powerful enough to blow away the ricers
oh and i have to do headers into cherry bombs so people can hear me coming

[Pont406]

600 is not too big. GM installed 800 cfm qjets on a smog 305 motors.

[toddtheodd]

Remember this formula.
Max RPM multiplied by Cubic Inches. Divide that number by 3456 (don't ask how to get that number... I can't remember but is has something to do with the number of cylinders and stuff).
The number you get is the maximum number of cubic feet per minute your motor can run at 100% efficiency.
So... a 350 with 5500 rpm red-line would work just fine on a 600cfm carb.
A 307 with a 5500 rpm red-line would probably do better with a 550 or 500 cfm carb.

Now for those that will argue bigger is better. A carb uses the venturi effect, which relies on the velocity of the air passing through the carb.
As long as you don't go too small (choking the engine), a smaller carb will give a better signal to the venturi's, and hence run better. Especially from a standing start. No bogging down.
Think of it like this... 3 gallons of water a minute through a garden hose will have more velocity than 3 gallons of water a minute through a sewage pipe.
Toad

[Green Machine]

If you are going with a square bore carb, take a look at the performer EPS, newer design and is designed for square bore only. 600 will be just fine IMHO.

[Jim_PA]

Can't we convine you to shelf the 307 for future originality, and drop in a crate 350 or something for the time being?

[bmrrwolfe]

I was thinking about it, but it runs good, im not trying to make a race truck, just a good daily driver, with the small addition of a few cheap parts to make a bit more power.
im sure in a year or two i will put a 350 in it, but being 18 and having an extremely limited budget, and having alot of other work the truck needs im gonna stick with it. and i can always reuse in the manifold and carb for it.

[Jim_PA]

Usually a re-build is more expensive than a GM 260 horse crate.

plus... you get a warranty with the crate... A few years from now, you can swap heads and cam, and be in the 350+ HP range

[spinning wheels]

Originally Posted by toddtheodd

Remember this formula.
Max RPM multiplied by Cubic Inches. Divide that number by 3456 (don't ask how to get that number... I can't remember but is has something to do with the number of cylinders and stuff).
The number you get is the maximum number of cubic feet per minute your motor can run at 100% efficiency.
So... a 350 with 5500 rpm red-line would work just fine on a 600cfm carb.
A 307 with a 5500 rpm red-line would probably do better with a 550 or 500 cfm carb.

Now for those that will argue bigger is better. A carb uses the venturi effect, which relies on the velocity of the air passing through the carb.
As long as you don't go too small (choking the engine), a smaller carb will give a better signal to the venturi's, and hence run better. Especially from a standing start. No bogging down.
Think of it like this... 3 gallons of water a minute through a garden hose will have more velocity than 3 gallons of water a minute through a sewage pipe.
Toad

Toddtheodd, most of your info is correct, and I have read those CFM flow charts and it is very good advise. However, there are always exceptions. My '70 Z28, with a SBC engine came stock from the factory with a Holley dual feed, double pumper 780 CFM carb. A lot goes into carb tuning and it would take pages to explain tuning theories and practical tuning. Not to mention head flow, cams, and damn it never ends.

A 307, will run fine with a 600 cfm carb.