I know about blocking off exhaust crossovers when installing intake manifold gaskets, but I am curious about the exhaust crossover restrictors that come with new Fel-Pro intake gaskets. Certain model years used them on one side only, while other years (like ours) did not use any. What is the purpose of "restricting" the exhaust crossover flow versus leaving it open or completely blocking it off? Is there any benefit to installing it on a thirdgen?...

 

Different intake manifolds, in their intended factory configurations, wanted different amounts of heat, depending on the routing of the exhaust passages within the intake.

Our cars don't need as much as some. 60s cars, with the passage right immediately under the front of the carb, need even less. Those need both of them.

No restrictors is probably too much heat for setups like ours. Some of ours need at least 1. Ones with highly restrictive exhaust systems (LG4) probably need none. It's kind of a judgment call in a way. It's really an emissions matter at its core, not so much how the car runs or any of that.

 

Like Sofa said, it's basically heat for the carb/choke. Remember the divorced chokes with the coil on the intake and the rod connecting to the carb?
I don't think that many of us are regularly driving their cars in the winter. We install aluminum intake manifolds for a cooler fuel charge. Air-gap takes
that a step further. If you block both ports, you would have a little longer warm-up time until the manifold heats up. All mostly for emissions.
I block both of mine.