I'm replacing the exhaust on my '64 365HP with a stock system from Allen's. It currently does not have a heat riser valve. Should I put one on it, or use a spacer? Not racing or anything - just weekend cruising. Thanks

Gary

 

You may have to include a spacer or a heat riser because the system was probably measured to include that dimension. I put Allen side pipes on my 66 and the passenger side would not fit properly without that spacer/riser in place.

 

do you drive your C2 in the Winter (in Michigan, that's the months on either side of July ) ? I am in CT, I drive mine up unitl the first snow / sand and salt, then it's up until the melting is done. I replaced the "heat riser" valve (serves to block the p-side exhaust and force exhaust up and through the intake manifold exhaust cross-over) with the solid "FI" spacer, and have never had any issues. Agree it's got to be one or the other, for fitment purposes. And, if you have severely restricted or blocked the cross-over (perhaps just on one side) then you must ensure your heat riser is wired open or use the FI spacer.

 

You need the FI spacer or the heat riser valve to make the right side of the exhaust system fit right. They are both the same thickness. Either one will work for you. When you get your new system, make sure you have the gaskets, the "donuts," the spacer or valve, and the inserts. I forget what the inserts are called. They go in the junction of the manifold and pipe to protect the donut from being blown out. Use brass nuts to cinch the pipe flanges to the manifold studs. If you're real fancy, and you dare to remove the studs in the manifolds, replace them with stainless steel studs.

The heat riser valve aids engine driveability while the engine warms up. It also speeds the warm up process. It is a thermostatic thing that is closed when cold and opens when it warms up. When it's closed, it forces exhaust gases from the right cylinder bank up through a passage in the intake manifold. That crossover passsage is routed under the carburetor. Some people block that passage to aid in keeping the carb cool. If you blocked that passage (like I did), and the exhaust valve failed (which they do all the time), these gases would have no place to go, and you'd be screwed (technical term).

When I did mine (also from Allen's), I used the FI spacer, because I didn't want to take the chance of it failing, and I never drive the car in the cold weather. In retrospect, I'd rather have the valve for appearance sake. When I get the chance (This is not high on my priority list.), I'm going to replace the spacer with a modified valve. The modification to the valve will be for me to gut it. Take a Dremel tool to the butterfly valve inside and remove it. In place, it'll look like the valve, but I will have "Murphy proofed" it.

 

Here is a tip from the NCRS board. The best thing you can do with a heat riser is take a die grinder and remove the butterfly plate from the shaft before you install it. Then you have the original look of the valve installed and none of the problems associated with the valve.

 

C2IT, as I recall, when I did mine, I cut the butterfly shaft out of the unit, then tapped the hole in the body of the riser and put a short machine bolt in it with exhaust sealer on the threads. I believe the butterfly shaft only goes through one side of the body, and you'll never have to worry about exhaust restriction due to a stuck butterfly.

 

Thanks for all the input, guys. Although I am an NCRS member, this car will never be flight judged (at least not while I own it), so I think I'll go with the spacer.

 

and it's not like a huge task to put the valve unit back in if you ever change your mind.

p.s. I have NEVER noticed any driveability issues attributable to being without the heat riser, but then again I am not diving in below freezing temps.

 

FWIW I didn't even need the spacer on mine no clearance issues a friend has a 66 and he's not running a spacer either.. You may or may not need it with the Allen's. BTW both of our cars have Allen's side exhaust.... Dave...

 

There is a person on e-bay ( CHEVY BOW TIE - GUY ) selling " original GM big block" heat risers for 50 plus 7 shipping. He sends you a reproduction made in Canada. Your local GM dealer can get you one for about 40.00 if you can talk him into a discount. One of these days he will meet someone who does not have a sense of humor...