Carb Bolt Patterns

I've gotten myself a little confused about spreadbore & squarebore. I've got an old edelbrock C3B intake manifold, is this a squarebore or spreadbore manifold? I know it was made for a holley 3bbl carb. What patern is a Holley? Rochester 4GC? AFB? Edelbrock? I know just enough to get confused...if anyone could clear it up that would be great.

 

I'll give it a shot.

The early 4bbls were mostly a very small bolt pattern, common ones include the 4GC and carter WCFB. Next up in size is the spreadbore Quadrajet. Then there is the standard Holley pattern, which is the same as the AFB, the bolt holes are on a wider pattern than the spreadbore.

AFBs and Edelbrocks have both the spreadbore and Holley bolt patterns. Some earlier design intakes only work with the AFB/Edelbrock style carbs, specifically dual quad intakes.

If an intake was made to fit the Holley 3bbl, then it is the standard Holley pattern, and you can put a Holley or AFB or Edelbrock on it.

This gasket



has the AFB/Edelbrock bolt patterns, the "inner" set of bolt holes is the same as the spreadbore, the outer set is the same as the Holley.

This gasket is for a "square bore" carb, and the center part can be removed to work with an open plenum intake.

This gasket



is for a spreadbore carb, notice the primary throttle bores are spread apart.

 

I have used Edelbrock Adapter Plate EDL-2732 to properly fit an Edelbrock or Carter AFB carb on an Edelbrock C3B manifold. Without the plate it is possible to have a vacuum leak.

 

Is there an adapter that would allow me to run a Rochester 4GC on an Edelbrock C3B Manifold?

 

There sure is...go to your local NAPA and ask for part number #735-4927

 

Thanks, ****ster, Bobw, and Squirell.