carb size?

[carolina pyro]

hey guys iv got a problem i hope yall can help me with. the car is a 67 chevelle ss. 402 .40 over closed chamber heads balanced and blue printed, w/ summit 292 cam with a turbo 400 and a 12 blt posi out back. it runs strong but i only have a holly 670 street avenger on it i know thats way to small. but i was wondering how big i should go without putting too much gas in to fast. i prefer a carb with a vacum secondary.
Help will be appriciated.

[NOVA71]

I'd say a 750 would be all that you'd really need but, you could probably go as high as an 850. A little bigger wouldn't hurt if your going with a vac secondary since the secondaries will only open enough to suppy the need of the engine. Also, I find vac secondaries a little better for street use. I run a 650 Speed Demon with vac secondaries on my 350 Nova and it works great. You should check out the Demon website, they have some good info. there. This is the link;

http://www.barrygrant.com/

If you scroll to the bottom, there is a Demon selection guide that you can click on about choosing the proper size carb for your engine and cam requirements. Alot of the info would hold true for any carb, not just Demons. Hope this helps ya some.

[carolina pyro]

cool car, thanks alot

[SpinnerCee]

I agree -- a Holley 3310, 750 CFM w/ vacuum secondaries would be the best for the street.

http://store.summitracing.com/partde...5&autoview=sku

http://store.summitracing.com/partde...3&autoview=sku

[LawmanD]

Originally Posted by carolina pyro

hey guys iv got a problem i hope yall can help me with. the car is a 67 chevelle ss. 402 .40 over closed chamber heads balanced and blue printed, w/ summit 292 cam with a turbo 400 and a 12 blt posi out back. it runs strong but i only have a holly 670 street avenger on it i know thats way to small. but i was wondering how big i should go without putting too much gas in to fast. i prefer a carb with a vacum secondary.
Help will be appriciated.

You don't say what rear gears you are running, or how loose your convertor is, but we ran 4.56 gears with a convertor that would flash to 3000, and a 750 double pumper worked a whole lot better for us in a 3300# car than the 3310 vac. The 3310 wanted to be lazy til the boosters caught up. The 30cc shot from the back barrels would really kick it in the tail right off the line without any hesitation! Just my opinion.