570 or 670

[79bonanza]

Ok I'm picking a carb for my 85 crew cab. It has a eldebrock intake and hooker headers on it, other than that it's stock.

I like the holly street avenger carbs so I'm prolly gonna go with one of those but idk weather to go with a 570 or a 670.

What do you guys think.

Ohh it's a th400 454 combo

 

[black dawg]

If it isnt gonna get revved on, I would go with the smaller carb.

 

[diesel4me]

I've used 4 barrel carbs as small as 450 CFM's on stock 454's and had them run great on the street...Oldsmobile used the larger 2GC Rochester 2 BBl carbs on early 455's and they had better low end torque and some of the 4 bbl carbs did.."leaner is meaner" was a common saying back in the day...

A carb with vacuum secondaries like a Q-jet or spread bore holley you can go "bigger" CFM's and it'll self compenstate by only allowing the secondaries to open when the engine can use all that air and fuel,and will aid in giving better economy.....but for most practical daily drivers I'd say 600 CFM or less is plently,only if you have a hotter cam & headers is a bigger carb going to be more desireable,and if you run it at high revs, like on the racetrack..otherwise your just wasting gas,really..a double pumper with mechanical secondaries is probably the worst choice for street driving with a stock engine ,it'll get about 3 mpg and wash the rings out..

 

[79bonanza]

Ok I was thinking about running the smaller carb anyway, so that sounds like what I'll run. Thanks guys