Such a loaded question.

What manifold,  what carburetor,  what cam grind?

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Edlebrock performer, 850 Holley marine is the one I was thinking. Not sure on grind


Sent from somewhere in Cali

I have had a lot of success running a 1" spacer on open manifolds. On the performer, I would try just a gasket to take full advantage of the dual plane,  maybe even try a four hole spacer,  not open.

GT

Such a loaded question.

What manifold,  what carburetor,  what cam grind?

Sent from my SCH-I545 using SoCal Jet Boats mobile app

 So true, "such a loaded question".

 This is just my own experience with a performer intake.
 Idle quality and off idle throttle response was best with no spacer and a gasket that sealed the intakes center divider (no open center gaskets).  Even an open center 1/4" spacer/gasket would hurt idle quality and off idle throttle response slightly.  But even the 1/4" open spacer seemed to help a bit at high RPM.  If you look at the higher RPM range dual plain intakes (performer rpm, etc) the center divider in the intake is dropped below the carb mounting flange. 

 I would agree with GT as a start, depending on intended use/application. Then later if you think a little extra top end might be helpful try a small open spacer. An open spacer will not turn a performer into a performer RPM.  And the spacer might not make any improvement, depends on you max RPM.