Holley 850 vac sec, elec choke.

Going on a mostly street /weekend cruiser/ occasional strip car.
489ci brodix oval,solid roller.

What do ya think?

Can these be "tricked out" anymore to run better?


Mitch

If that's the 502 take-off carb - there very nice. Its a 4150 style (2 metering blocks, and come with jetting pretty darn close for what your doing. I've seen them on EBAY brand new for ~200-250.00. Its a 400.00+ carb brand new.

Carb would be perfect IMHO

That's what's on my boat--454

Carb cfm = (engine cid * maximum rpm)/ 3456

So since its a street car you'll probably never rev it over 6k? So that'll put your cfm at 848... But then you factor in volumetric effeiceny which I don't understand yet and that'll lower it even more... I have a 850 dp on my 454 and I love it but I get told all the time that a 750 would be better quicker throttle response and the such.... but I'm new to this

I was leaning towards a 750 but I see these on ebay going pretty darn cheap, and yes it is off a zz502.

Thanks,Mitch

Yeah I scored a 750 vacuum secondaries this guy was runnin on his camaro with a 350 for like 80 bucks holley there's tons of books on how to rebuild them and I think the kits run like 30 dollars? Buddy just had his rochester rebuilt for 150 bucks in his 64 impala

[QUOTE=Davec43]Carb cfm = (engine cid * maximum rpm)/ 3456

Yeah, that's correct as far as it goes.

Problem 1. Inconsistent rating methods. Is the carb you buy rated DRY flow, or WET flow. Actually pulling fuel through it will reduce the CFM. I don't know how Holleys are rated.

Problem 2. 4-barrel carbs are usually rated at 1.5 inches of vacuum. But if you have that much vacuum in the manifold, power suffers. Less vacuum will pull less air. So, for max power, you need a larger carb than what the formula will tell you.

Problem 3. The intake manifold has a great deal to do with how much air the carb can pass. A single plane manifold will allow a given carb to flow more than a dual-plane. Dual plane manifolds with the divider cut down function somewhat more like a single-plane, and so you can tune them by varying the size of the cut on the divider. A dual plane that is completely seperate will flow less still, because the carb sees "pulses" of vacuum alternating to the left and right halves rather than more steady vacuum drawing on both sides at the same time. So the carb isn't flowing as "constantly" as with a single plane.

If you dig through the Edelbrock site, they give the formula above, and you plug in your RPM and displacement, and get whatever the result is. Then you multiply by the expected volumetric efficiency--often "about" 0.8. THEN, you multiply by a correction factor based on whether you have a single plane or dual plane manifold. In the end, it often comes out about the same or a little LARGER than the result of the formula above.

http://www.edelbrock.com/automotive/math.html then scroll about half-way down the page 'til you get to "About Cubic Inches, Volumetric Efficiency,
Flow Bench Conversion and CFM", then scroll down farther to "CFM Rules..."

Remember, the crappy booster venturis in the typical 3310 Holley leave a lot to be desired. Yet another reason to go with the 850 Vacuum 502 carb. Better boosters mean more signal to pull fuel. The 850 can be just a responsive as the 750 because the 750 has poorer signal.