I'm purchasing a 428 bored .40 over w/62 heads, ram air IV cam, stock intake. How do I determine the size of carb I need?

Sounds like 750 cfm territory.

Are you going with a Q-jet or somthing Else? If your going the Q-jet route its not really a concern.

I'm not sure what to go with. It has a stock intake. Looking to get the most power and reliability out of it. Would like to have mechanical secondaries as well.

Best bet would be to have Cliff Ruggles custom build a quadrajet for you. IMO

Something tells me thats going to be spendy. How do I get ahold of him? Thanks for the help

I'm with Jim regarding size. However, you can call Holley tech support. They'll calculate your need based on Cubes, RPM, and volumetric efficiency...and probably come up with the same reccomendation. Not so critical on a vacuum secondary carb.

You may want to reconsider the manual secondaries. I've been advised that they will affect drivability on a "heavy" street car with an automatic tranny(our 'birds aren't considered light in weight). If you're building a racer, do it!

The rule of thumb is the follwing equation:

Displacment x Max RPM x Volumetric Efficiency %(approx .80 for street engines) divided by 3456.

The bigger carb may gain more HP on the top end, but at the expense of low end performance. For a street engine, error to the smaller side.

If you use a 800 cfm Edelbrock AVS (Air Valve Secondary) you will have a good carburator.

-The Air valve will only open to match the engines needs (You might only need 700, 740, 780 or whatever)

It's not always true that a big carb will be a bad choice. -Same with the relatively big q-jets (780-800 cfm.)

Cliff's;

http://www.cliffshighperformance.com/

OK fbody69, I went to cliffs web site and started to request a quote. They were asking for rear end ratio and I don't know what was offered in 68. It appears to be a highway gear, runs about 3000-3500 around 70mph w/stock ohc 6er. Also is posi. Forgive me for my ignorance.

Tell them you have 2.56 gears. Could also be 3.08.