Quote Originally Posted by DennyW
Pretty much what was said. How ever, you can try a 1" spacer with the 4 holes (closed), not open. This will speed up the velocity for take off.

This the manifold you have ?
I was reading my Holley handbook and in chapter 8 it was talking about adapters. They claim that a 3310 rated at 780 cfm drops to 640 cfm when an adapter is used.
I've got the 650 dp mounted on the 289 in the Mustang with a 1in spacer. By their calculations that must drop the cfm to somewhere around 525. Does that make sense?