These were between the passenger side exhaust manifold and the pipe that goes to the cat. Whats are they for and are they needed when reassembling?

 

That used to be one single part...

Yes it's necessary, if for no other reason, than that the flange on the Y-pipe won't bolt to the manifold without it.

Its "official" name is "heat riser valve" or "EFE valve". Its purpose is to close when vacuum is applied, which is only when the coolant is below about 120° or some such; it sends all the right bank exhaust through the intake and over to the left manifold, for faster warmups.

 

NO!,
Yes its called EFE, use on carb motors to place a load on the engine to help in warm-up. It does not send exhust flow to the other side. These are not required for Fual Injected Engines.

 

Ok, my turn...

NO!

It's not to place a load on the engine, it's to send exhaust flow to the other side through the crossover ports in the heads and intake, exactly as Sofa says.

 

Gee
That real funny.
My 82 Firebird came with LG4 305 carb motor. There were no pipes connecting one side of the engine to other. The fact is the EFE does place a load on the engine to help the engine warm up faster. If you rev the motor while cold the vacum will drop and the valve will open to allow exhust flow.

 

There are no external pipes connecting the two sides. There are internal ones, which are the aforementioned exhaust crossover passages (note the name) in the heads, and under the intake.

EFE uses exhaust heat to warm the intake so that cold fuel evaporates instead of puddling.

 

Unless there are emissions issues, you would probably block off the crossover on a new intake manifold install anyways.