Re: will a squarebore to spreadbore adapter plate effect performance?
From Dennis Moore:
CARBURETOR TO MANIFOLD ADAPTERS
When General Motors' Rochester Division decided to quit making the
Quadrajet carburetor, Mercruiser switched to the Weber carburetor.
Unfortunately the Quadrajet four barrel is a spread bore design
carburetor and the Weber is a square bore. All Chevrolet marine engines
with standard performance intake manifolds have the Quadrajet spread
bore carburetor mounting flange. An adapter is used by Mercruiser to
mount the square bore Weber carburetor on the spread bore manifold. This is not an ideal situation, to say the least, for maximum performance. The Rochester Quadrajet is one of the finest carburetors ever built It has
been discontinued because the entire automotive industry has converted to
fuel injection. Purchasing a used Quadrajet marine carburetor from a
Boat dealer and installing it in place of the Weber,and doing away with the
adapter,would be an excellent idea. The Weber four-barrel is also an
excellent carburetor. Installing a square bore intake manifold while
retaining the original Weber carburetor would be another good
option in order to do away with the adapter. Either way,getting rid of the
adapter should be one of your first steps for increased engine
performance.