I would like to block off the heat cross over on my aluminum intake.  What is best way since my gasket has a metal plate with a hole. Or is it really necessary to block this off.
thank you,
Richard

What intake manifold?  The Mummert does not have the passage, so no issue.  If BT, then you can cut a simple piece of tin/sheetmetal out of a tin can lid and bend a simple 90* lip to hold the tin in place, remove the metal from the intake gasket, and install the manifold like normal.  Joe-JDC

JDC

Richard, if you have Mummert aluminum heads, I don't think they have the heat crossover, in which case there would be no need to block the crossover on the Blue Thunder intake manifold. 

Ok, Mummert heads have the hole as does the BT intake.  I’ll cut a can, and 
thanks

Mummert heads haven't been drilled through to the exhaust valve port.  Joe-JDC

JDC

Taking into consideration that the Mummert aluminum intake manifold does not have the heat crossover for the choke, I don't know why his aluminum heads would have it. 

Having an electric choke, 57 "B" intake and "G" heads, I will block off the crossover at the heads when my heads are done. 

By now I suspect many of us have done this mod.  I recently blocked off the cross over gasket holes to my "B" manifold and it was a big improvement.  I was getting all kinds of intermittent heat soak issues and finally broke down and pulled my manifold.  This mod reduces the heat to the intake manifold substantially.  So much so that you can feel the difference with the hood open. It's probably my imagination, but the engine seems to have a little more power with the holes blocked.

Repeating what Joe has mentioned, the Mummert aluminum cylinder heads have the capability of having a heated crossover although as delivered, they are blocked internally.  To make the heated crossover functional, it is required to drill a hole through that blockage to the exhaust port.  To date, I have not had a request for a heated crossover when installing the aluminum heads.

The Mummert heads are designed to use both stock intake and exhaust manifolds and for that reason retained the capability to use the heated crossover if desired.  The Mummert intake manifold went the way of most aftermarket intake manifolds in doing away with the heated crossover but the Blue Thunder intake manifolds do still retain the heated crossover capability.  From a performance standpoint, the elimination of the heated crossover and running a cooler fuel mixture at the intake manifold plenum is desirable.  For those areas of the country where the ambient temperature falls below the dew point, then the heated crossover does keep the carburetor warmer and minimizes potential icing issues.

For most warm weather applications, I block the heated crossover at the intake gasket with a piece of 0.020” shim stock.  Removing the existing tin from the intake gasket at the crossover port and replacing it with the shim stock has the gasket distortion being the same as originally intended.  Many of the Thunderbird owners request the blocked crossover passage option when rebuilding their engines to prevent the paint from burning at the intake manifold.

Lorena, Texas (South of Waco)

Ted,
thank you very much for the info.
Richard