C3 - heat riser

[Jim Callan]

I will be replacing the exhaust system soon on my '71 270hp. When I removed the exhaust manifolds, I noticed the heat riser was "froze" in the open position. The new system includes a new heat riser, but is there any reason to replace it ? The car has lived in Florida and Georgia for the last 20 years and I'm sure the riser has been froze for the last 15 years. If I do leave it alone, do I have to plug the intake cross-over holes ?

Thanks

Jim Callan

[Ralph A.]

Re: C3 - heat riser

If you ever plan to judge the car the heat riser will need to work to get full credit during operation check and mechanical sections.

[Jim Callan]

Re: C3 - heat riser

This car is original and I have owned it since 1973 but is driven, so won't be chasing points. The car now lives in GA and not concerned about cold weather warm ups.

Thanks

[John H.]

Re: C3 - heat riser

Even if you don't need the heat riser function, you'll either need it or an equivalent spacer (like the F.I. cars used) to go between the manifold outlet and the exhaust pipe or the pipe won't fit properly.

[John H.]

Re: C3 - heat riser - Addendum

Also, you won't be able to seal the "donut" on the exhaust pipe directly to the manifold outlet surface; the donut requires a beveled surface to seat against, and the manifold outlet surface is flat (to accept a gasket for the heat riser); the top surface of the heat riser is flat (as is the top surface of the F.I. spacer), and the bottom surface of both the heat riser and the spacer are beveled to accept the "donut". You need one or the other.

[Gerard Q.]

Re: C3 - heat riser - Addendum

What a lot of folks do is wire it open.

[Jim Callan]

Re: C3 - heat riser - Addendum

I was going to use the riser that is 'frozen' open. Should I leave the intake cross-overs blocked or both sides open? When I removed intake, both sides were open.

Thanks

[Joe L.]

Re: C3 - heat riser - Addendum

Jim------

You can't block the intake manifold cross-over passage or your choke will be completely dis-functional. Then, you'll have to use a carb with an electric choke.

Also, I would never recommend blocking the crossover passage unless the heat riser is rendered absolutely, positively permanently open, either by removing the butterfly valve or replacing it with a spacer. Having it be "stuck open" or, even, wired open does not, in my mind, constitute the valve being absolutely, positively permanently open.