I just bought a new 600 cfm Holley to go on my 65' vette, that has had the engine replaced with a 1970 Camaro 350 cid lightly modified I was told. When I pulled the "leaky" Holley that was on it, I discovered it had a spread bore intake. Holley said I could just use the square bore gasket and bolt it on - no problem. The old carb, square bore, leaked a little gas on the intake, but started and ran fine - not sure on any performance loss/gain. I'm thinking I should exchange it for a Holley spread bore carb. Any experience or advice will be greatly appreciated. I don't want to change the intake.

 

Personally I would exchange it for a Quadrajet. But that's just me. That being said, a spread bore such as the Quadrajet has several advantages to a square bore. First it is a more economical carburetor because when operating on the primaries it is using less gas. When you want to get on it, and the secondaries open up, you have the benefit of a much larger carburetor and it allows the engine to breathe easier. While I've had no first-hand experience with the Holley spread bore, I've heard others comment about it and they weren't positive.
Let us know which way you decide to go and how it works out for you.

 

Does QF or ProForm make a spread bore carburetor? Their quality control and tuneability are really good.

 

Haven't heard of them but have you tried contacting them?