[carbking]

Originally Posted by 61-63

Jeff Chmura Stray Cat makes a good point. If you go looking on ebay, craigslist, and other places for a used offy intake be sure to get one with the adapters already on it. You will see them offered without the adapters and you don't want that because the adapters will cost you almost as much as the intake new and they are almost impossible to find used. Just keep looking and one with adapters will turn up.

Bill I've only done sets using the original AFBs so can't help with your question. Perhaps carbking can.

I don't have access to a dyno, which is why I normally post in the "street" section. My "dyno" is happy customers.

So I cannot tell you from experience if (2) genuine Carter 625's will support 469 HP, but Carter literature suggests they will.

Far easier to make any carb race well (WOT consideration only) than perform well on the street (idle, off-idle, various values of vacuum, transition, etc., as well as WOT).

Personal experience, with a LOT of testing:

I currently have two vehicles with performance engines: (1) Pontiac 350 with 850 CFM single spread-bore Carter carb, and (2) Ford modified 390 with two heavily modified Carter aftermarket 625 AFB's (similarity to Bill's question).

When I first put the two 625's on the 390, as always, I built them bone stock. They ran, actually pretty good, and many would have been happy. I wasn't satisfied. So I found a pair of 430 Lincoln AFB's, and transferred primary clusters, secondary clusters, auxiliary air valves, primary jets, secondary jets, step-up rods, and vacuum springs. MUCH BETTER, but still not happy. Changed the mid-range vacuum step on both step-up rods to eliminate a mild surge at cruise. Now it runs the way a carbureted engine should run; and a youngster (then about 25) insulted me by asking what fuel injection unit I was using!

Tom S. made the comment that the imitation AFB's race better than street use. The aftermarket Carters with which I started fit that description, because Carter calibrated them for Chevrolet. The calibration curve for Chevrolet is totally different than the curve for Ford, or Pontiac. If fact, the Ford curve is very close to the one for Pontiac (the Chrysler curve is even closer to Pontiac).

So your 625 Carters will probably race well as is, better with minor tweaking, but will require surgery to run well on the street. But "running well" is a subjective term, different folks will have different tolerances.

For street use, we generally suggest using a couple of original Pontiac single AFB's as the calibration curve is close, and only minor tweaking is generally necessary. Doesn't really matter which Pontiac AFB, as long as the two are the same. We generally suggest either 3300s or 3326s (these two MAY be mixed or matched), as they are relatively easy to find, and relatively inexpensive.

Jon.