Carb for a 307???

[chevyc1068]

What would you guys recommend for a carb for a 307? I'm talking CFM, secondaries, what make and model that sort of thing. I'm looking at the Holley 4160 600CFM manual choke, but I want to know if that is to much CFM. I've heard if you get to much CFM that it will cause bogging and bad fuel economy. Or if I do get it is there something I can do to make it better. Like change jet sizes, or tune it someway or the other???

[pissonNOS]

i have an AFB CARTER on mine i believe it is 625 CFM i dont have any problems once in a while it will bog down when you pin it but thats it i think youll be safe with 600

[Slammed70]

Manual choke.....why?

600 is kind of on the big side for a small, Im assuming stock engine. But you should be fine.

Im running a Holley Street Avenger 770CFM (I know it huge, its a long story) and the only problem Ive ran into was finding an aircleaner to clear the bowls.

[chevyc1068]

What kind of secondaries does it have on it? Whats the difference and advantage of vacuum secondaries or mechanical? Does it matter?

[chevyc1068]

Thats what came stock on it was a manual choke. Besides I like them they are easier to use and you can turn it on whenever you need to if you need to. This will not be a stock engine. It will have a new cam and lifters in it, new manifold, new carb of course, headers, dual exhaust.

Slammed70, what size of engine are you running???

[Slammed70]

Originally Posted by chevyc1068

Slammed70, what size of engine are you running???

Im still running the stock, original, leaky, smoking, tired, worn out, factory 327

I know where your coming from on the manual scoke, I had one on my S-10...it was $15 cheaper then its electric brother. But Im lazy now.

[brak]

you want to match the carb to the intake, and the intake manufacturer will tell you specifically (in the documentation) what carbs are acceptable

Stock to mild intake (ie edelbrock performer) 600 to 650 would be about right.

performance intake (ie edelbrock performer RPM) 750 and up.

[chevyc1068]

Mine will fall into the stock to mild performance category.

I agree I will probably after a few years wish that I would have got an electric one. Can you get a manual to electric choke conversion kit, or is it only electric to manual?

[lilpup69chevy]

i'd say go with an edelbrock performer carb 600 cfm electric choke you will be darn pleased with it on a stock or hopped up engine, i always have been

[Sweet72]

You can re-jet that holley for your engine if you can pull a plug and read it, you can get it right with a little patients. Go to the Holley site and mortec. http://www.mortec.com/carbtip1.htm

[KSCHEVYUP]

You are on the right track. The biggest mistake most people make is by putting to big of a carburetor on. Do your research and go with what the manufacturers (intake manifold and carb) recommend. They have spent millions on research and know more than us shade trees. My personal preference is vacuum secondaries for a street machine unless you really have a fire breathing monstor. Vacuum secondary carb will also be more forgiving and easier to drive if you happen to go a little big for your application. If you add hedders and bigger cam at later date it will adust to that to some degree as your motor flows more cfm. I have had mechanical (vacuum operated) chokes; electric chokes; and no chokes; but my personal preference on daily driver is electric. It's really personal preference. There is nothing wrong with a hand choke at all and requires very little maintenance and is easy to set.
Just my .02 cents worth. Good luck

[Billla]

Originally Posted by pissonNOS

i think youll be safe with 600

600 CFM is plenty. Electric choke, vacuum secondaries.

[Billla]

Originally Posted by chevyc1068

Whats the difference and advantage of vacuum secondaries or mechanical? Does it matter?

Vacuum secondaries open based on engine load, mechanicals open at a set point in throttle travel. For a racing engine mechanical secondaries ensure no "bog" when the extra capacity of the secondaries is required. On the street, mechanical secondaries just eat gas and driveability - even if tuned correctly. Vacuum secondaries may also require a bit of tuning to avoid a bog but it's not all that hard. The Edelbrock is FAR EASIER to do this tuning on than the Holleys are IMHO.

[chevyc1068]

Billa, what is the "plenty" supposed to mean? Is that saying that that might be too much or just right? I don't want to have an undrivable machine.

[Billla]

Originally Posted by chevyc1068

Billa, what is the "plenty" supposed to mean? Is that saying that that might be too much or just right? I don't want to have an undrivable machine.

Sorry, the bold was probably a bit too much My comment was to indicate that anything BIGGER was not needed. I'll plagerize one of my responses from another thread:

Too much carb is the most common cause of poor throttle response and poor milage. Remember the basic formula for carbs:

CFM = ((CI x RPM)/3456) x VE

VE will be 75%-80% MAX for an engine making < 1 HP CID. Applying to your 307: 426 CFM = ((307 x 6000)/3456) x 80%. At 2000 RPM, you're flowing less than 300 (142) CFM...so for a square-bore carb a 600 CFM carb would keep you out of the secondaries in cruise.

[davidh]

Edelbrock also makes a 500cfm carb. I'm sure that would be good on the 283-307 range motors.

[Billla]

Originally Posted by davidh

Edelbrock also makes a 500cfm carb. I'm sure that would be good on the 283-307 range motors.

I wouldn't expect to have venturi size issues for a 600 for a 307. I'd be a bit worried that a 500 would see the secondaries too often in daily operation and would give less milage...and clearly wouldn't transplant to another - larger - engine in the future. I think a 600 is just fine IMHO.

[chevyc1068]

Thanks Billa that makes me feel better.

Anyone know of a superb 600cfm carb?

[Billla]

Originally Posted by chevyc1068

Thanks Billa that makes me feel better.

Anyone know of a superb 600cfm carb?

Most welcome I've always been a Holly guy, but I'm falling in love with the Edelbrocks for the street as they're MUCH easier to tune.