Well I've got a really bad rattle from the exhaust, I was told it is the Heat Riser.  What does the Heat Riser do?

Also I've got two choices, buy a new Heat Riser for $130 or weld it open for free. What do you suggest? I'm leaning towards welding it open for Nadda

Thanks for the advise.

There is a passage from one side of the engine to the other via the intake manifold and heads.  This passage supplies exhaust gasses for the EGR valve, when equipped with the valve.

The heat rises shuts due to heat and cold acting on a thermo spring.  When the engine is cold the heat riser shuts, restricting most of the exhaust gas from the right side of the engine.  This forced the exhaust gas up through and across the intake manifold.

The hot gas heats the intake.  This causes the cold fuel and air to heat and atomize better for better cold operation/running.  It also helps to allow the choke to open faster as a result, which helps cut cold emissions.

Once warm, the heat riser opens and allows full flow of exhaust from both sides of the engine.  With now fairly equal pressure on both sides of the intake, the exhaust gas flow stops, and quits preheating the intake.  If it stays shut when warm, the intake can overheat causing backfiring, hesitations, and vaporlocking.

Later versions were called EFE valves.  EFE is Early Fuel Evaporation.  These were vacuum controlled via a thermo vacuum switch on the intake in the water jacket.  So coolant temp controlled when it opened.

You can tack weld it open with no problems.  But you may find it takes longer to warm up the engine, and the choke may need adjusted to open a bit slower. This means emissions raises when cold, and fuel mileage drops a bit due to longer choke times.   A new one avoids this, but it's not severe if you chose not to replace it.  You may not notice much difference as long as it stays open.

Ken,

Is the heat riser anything "special" in Marks mainfold? Could he get a like riser from the wrecking yard? I relize this item takes alot of abuse and may not like being removed easily. It was just one of those outside of the box questions that might provide a little $$$$ relief to our Pacer friend...

You can remove the vaccuum line going to the heat riser. Most of the time, that eliminates the rattle, but it also renders the valve usless.(yeah, like it's not now?) This is just a test to verify the source of the noise.
I wouldn't weld the thing, meself. It can be mechanically fixed in the open position, without ruining the thing. One of theses days, you're gonna wish you hadn't welded that factory original part that no-one on the planet has!!!(Don't ask...)
The real problem is usually the vac. canister has ruptered, and it allows the valve to "flutter".

Wow great info guys  Should I have expected less  Thanks Ken and Joel.  I think I'm gonna have the thing welded open. I believe everthing can be found on eBay, I'll just keep my eyes open till I can find another on there then replace the welded one. I've gotta get rid of this rattle. Thanks again cilrah38869.1604050926

You can actually use a piece of wire or similar thing to secure the rod from the vacuum motor to the heat riser, and that will hold it still and stop a rattle as well.  Much easier than welding.

[QUOTE=kstyer] You can actually use a piece of wire or similar thing to secure the rod from the vacuum motor to the heat riser, and that will hold it still and stop a rattle as well.  Much easier than welding.[/QUOTE]

Hey!!! Dat's what I said!!! sorta...

Thanks again everyone  I had the guy who did the custom exhaust on my truck weld it open.  He also said there were two exhaust brackets missing so he replaced those also at a total cost of 0, zip, zilch, nada  And he said when I find a new Heat Riser, he will put it on for nothing.

Of course I've gotta go back to him when I do my dual Flowmasters

Oh ya not a rattle under the shark at all now