[HO455]

Originally Posted by garyd1961

Why would you run an open spacer on a duel plane intake.
.

I too have successfully used open spacers on dual plane manifolds. In my case it was on a .030 over 400 Pontiac with #62 heads I ported, a Ram IV cam and a set of 3 tube headers. After experimenting with several different combinations of spacers between the stock intake and the Q-jet I found that a 1/2" of stacked gaskets and metal plates that matched the intake holes topped by a 3/4" open spacer made the car quicker in the 1/8 mile. In addition and more important was that it moved the power band up slightly which made it easier to launch the car without spinning the slicks. Consistency wins races. And since it was my daily driver it definitely made the car easier to drive in the rain.
If the firing order of the engine and the physical layout of the intake manifold allowed exactly equal time between intake opening signals as they reached the carburetor then it is unlikely an open spacer would be helpful but since that isn't the case your trying to make the all the compromise work the best.
The picture shows a stock Honda manifold and if you think about it, it's basically half a dual plane manifold with a spacer on it. Just laid out differently.