My big block currently has a 'Brock spreadbore intake. Im running a 'Brock 750 carb....Performer, which is a squarebore. I recently added a phenolic spacer and Im wondering..is this spreadbore intake hindering performance because Im running a squarebore carb?

 

now that you have the spacer you should be fine. You only needed to get the little steel plate that Edelbrock sells to adapt the Sq bore to the Sp bore manny.

Massey

 

The spacer is squarebore, not flanged......standard summit phenolic spacer. While it has cured most of my carb/fuel cooking issues, I feel Ive lost some performance.

 

Are you saying you used a regular spacer, and not a square to spread adapter spacer?

 

...And if that is what you did, what did you do to prevent a vacuum leak at the base of the mis-matched spacer?

 

The plate I am talking about is Edelbrock part #2732 you can find it here on this page

Edelbrock.com - Installation Items - Adapters & Spacers

IT will prevent the vacuum leak that 69 is talking about. some other spacers don't seal the machine ports on the bottom of the Carter AFB/Edelbrock Performer series Carbs.

Massey

 

And.....the phenolic spacer you should have used would be the 4-hole type. That will give you a better "venturi effect", and better low-end torque.
A wide open spacer would instead be more for higher rpm response, as in the tunnel ram effect, but on a smaller scale.

 

The spacer is the 4 hole type. I put a 4 hole gasket between carb and spacer, and a open square gasket between the intake and carb.

 

Ok, but the opening for the secondaries on the spread bore intake manifold is wider than the square bore carb base, or gasket. If you're relying solely on the gasket, without an adapter plate, or a square to spread bore adapter spacer to seal that part of the manifold, you may be getting a vacuum leak there.

 

He's running like a champ for now. I was having MAJOR fuel boiling problems and the phenolic spacer has solved 85% of my hot running issues. This big block runs HOT....190 average with 210-215 in traffic. My goal for now is to just enjoy the car for another few weeks until the snow starts flying and I head out for the sandbox. Im beginning to assess my projects...replacing the 'Brock carb may be one of them. While the Brocks are SO much easier to adjust than a Holley.....they also seem to have so many more heat related problems.