What do you know about Heat Riser Functionality?

[Jeffery F.]

Recently had a N11 off road exhaust system installed on my '66 SB. I want to make sure the heat riser was re-installed correctly. After the engine has heated up, the heat riser valve attached below the right side exhaust manifold should automatically open; when the valve is open, should the counterbalance weight be up or down? Any advice is appreciated!

[Mark E.]

Re: What do you know about Heat Riser Functionality?

When cold, the bi-metal spring holds the weight up and the valve closed. As it warms up, the weight falls as spring tension relaxes, opening the valve.

For this to work, the valve must move easily. Check by pushing the weight down when cold. It should bounce back up to the closed position when released.

[Michael J.]

Re: What do you know about Heat Riser Functionality?

IMO, a heat riser is arguably the most poorly designed, unnecessary, and most unreliable part ever invented for a car.

[Gary C.]

Re: What do you know about Heat Riser Functionality?

Jeffrey,

Just wire it open with safety wire and don't worry about its operation.

Gary
....

[Mark F.]

Re: What do you know about Heat Riser Functionality?

IMO, a heat riser is arguably the most poorly designed, unnecessary, and most unreliable part ever invented for a car.

Agree 100% w/ Michael

Stupid device that only slightly improves (or maybe not?) a cold start/warmup cycle in COLD weather and then continues to offer compromised, uneven, unbalanced and obstructed exhaust gas flow on that side of the engine compared to the other side for the remainder of the time you drive the car (or just run the engine)...

I pulled mine out and replaced w/ a spacer 20+ years ago after I was done having my car judged... never looked back...

If you're going to have it judged, stick it in there and as Mark says make sure it flips easily...
pull it after judging if you drive your car...if not, leave it in, but it's a worthless part on your car no matter how you look at it.

[Leif A.]

Re: What do you know about Heat Riser Functionality?

Agree 100% w/ Michael

Stupid device that only slightly improves (or maybe not?) a cold start/warmup cycle in COLD weather and then continues to offer compromised, uneven, unbalanced and obstructed exhaust gas flow on that side of the engine compared to the other side for the remainder of the time you drive the car (or just run the engine)...

I pulled mine out and replaced w/ a spacer 20+ years ago after I was done having my car judged... never looked back...

If you're going to have it judged, stick it in there and as Mark says make sure it flips easily...
pull it after judging if you drive your car...if not, leave it in, but it's a worthless part on your car no matter how you look at it.

I pulled mine out years ago and Dremeled the flap out and re-installed...can't tell the difference from the outside. Best of both worlds.

[Larry E.]

Re: What do you know about Heat Riser Functionality?

FWIW>Yea just Dremeled my the flap out also. See my recent post. BTW> When I took it out I found the
flapper was rubbing against the "Exhaust Pipe Extension" Larry

[Duke W.]

Re: What do you know about Heat Riser Functionality?

IMO, a heat riser is arguably the most poorly designed, unnecessary, and most unreliable part ever invented for a car.

...just like the kitchen sink garbage disposal.

Actually, it did serve a purpose. Back when these cars were daily drivers they needed to be driven in the coldest weather, and the heat riser rapidly heated the manifold and base of the carburetor under the idle circuits to aid fuel vaporization, which allowed good "drive-off" performance shortly after a cold start in very cold weather.

But since we now rarely drive these cars in very cold weather they are of little use and can end up being a headache as they contribute to percolation problems in mild to hot weather and are subject to freezing closed, so wiring them open, removing the valve as described, or replacing them with the FI spacer is a good way to go.

Duke

[Mark F.]

Re: What do you know about Heat Riser Functionality?

I pulled mine out years ago and Dremeled the flap out and re-installed...can't tell the difference from the outside. Best of both worlds.

Leif,

Good approach !

Is flapper / counterweight proper functioning judged during Operations ? (been so long, I can't remember).

If so, whether the flapper guts are in there or not, the counterweight spring would still respond to the heat as it builds in the pipe, right ?

Response would probably be at a slower rate (no resistance to hot gas flow), but I'd think it should still work...

[Patrick H.]

Re: What do you know about Heat Riser Functionality?

Leif,

Good approach !

Is flapper / counterweight proper functioning judged during Operations ? (been so long, I can't remember).

If so, whether the flapper guts are in there or not, the counterweight spring would still respond to the heat as it builds in the pipe, right ?

Response would probably be at a slower rate (no resistance to hot gas flow), but I'd think it should still work...

Astute judges will note exhaust coming out the right-hand exhaust pipe on initial startup. This usually will not have you fail an Operations test, but definitely will fail a PV.

Of note, I have only had success with original NOS GM heat risers.
All of the replacements I have tried end up sticking.

[Leif A.]

Re: What do you know about Heat Riser Functionality?

Leif,

Good approach !

Is flapper / counterweight proper functioning judged during Operations ? (been so long, I can't remember).

If so, whether the flapper guts are in there or not, the counterweight spring would still respond to the heat as it builds in the pipe, right ?

Response would probably be at a slower rate (no resistance to hot gas flow), but I'd think it should still work...

Mark,
Externally, the heat riser functions as it should...undetectable that the flap is not there.
To Patrick's point, having had my car judged four times, no one ever mentioned the passenger side exhaust on cold start during OPS. If it was noted, it wasn't mentioned.
As to PV, mine has never been through and never will be.

[Tim G.]

Re: What do you know about Heat Riser Functionality?

Wire it open, but don't do as I do and forget to remove the wire if you have it judged. This will result in a deduction, and rightfully so. Ask me how I know.

[James W.]

[Keith M.]

Re: What do you know about Heat Riser Functionality?

Good discussion. In the middle of my restore and the riser I took off my 69 was defective. When cold there is a nub that hits against a stop to keep flap in fully closed position. Well the nub and stop were so worn the spring sent the assembly past the stop resulting in the flap being open from the other side. So I guess that instead of the flap going from closed to open on startup..it was going from open to closed to open as the spring warmed up. In any event I have accumulated a NOS riser and just recently grabbed a 2" GM spacer. So I got options. As for the original riser I could cut out the flap and go that route....but wonder if any judge would notice when cold the spring and weight are overly unsprung!
Keith

[Chris H.]