I've got a Holley right now but I'm open to changing....especially on the new engine.

Heard good things about "Demon" carbs.

The speed shop I deal with likes Demon carbs as well. They refer to them as "Holley's that work".

Personally, if you don't want a good Q-Jet, I'm partial to Edelbrock carbs. They're simple to deal with and hold their adjustments and have no power valves to blow out like a Holley.

But...if you plan on doing any track work, I'd go with Demon...street and cruising only I'd go with the Edelbrock.

How does one go about picking the right size Carb? Is there a formula?

There is a formula but GM recommends a carb in the 750 cfm range for a ZZ4. Normally the formula would work out to a recommended 600-650 cfm carb, but with the high lift cam of the ZZ4 and the fact that it makes its peak horsepower and torque at higher rpm's they recommend the bigger carb.

If you put a 600-650 carb on that engne, you might improve the low end driveability, particularly at take-off, but lose on the high end.

Keeping in mind GM recommends a 750 cfm for a ZZ4, here's the formula I copied and pasted from another website:

A larger carburetor or throttle body will enable the engine to draw in more air, but one that is too big is almost as bad as one that is too small. On a fuel-injected car, a throttle body that is too big will put too much gas in the combustion chamber that just flows the exhaust unburnt. It is much more of a problem on a carbureted car. There, an oversized carb will make the engine actually perform worst at part throttle. A simple formula for calculating the correct carburetor setup is:

CFM (amount of air the engine needs) = Displacement (in cubic inches) X Maximum RPM / 3,456


The result is usually rounded up to the next largest off the shelf carburetor sized. Therefore, a Chevy 350 built to redline at 6,000 rpm would need 608 cfm of air flow (350x6000/3456). A Holley 4150 carb rated at 650 cfm would be a good choice. For multi-carb setups, don't forget to add up the CFMs for each carb!

Once you find the right carburetor, keeping it tuned correctly is key. Also, carb spacers and carb re-jetting usually help, but it requires trial and error to find the best combination.

holley site has all the info. just put in c.i and it will lead you through and tell you whats,what