Heat Riser - Before I burn a valve...

[davepl]

I noticed that even fully warmed up (hot, actually) I was still getting most of my exhaust out the driver's side pipe.

I checked and the heat riser is -just- on the edge of closing. If you blip the throttle, it's enough to open it further. So it's just balanced against the spring pressure.

I expected, however, that by this time it'd be fully open.

Does the thermal spring on them work to close the valve, and just does less once hot? Such that they require the exhaust flow to actually do the work of opening it?

I didn't boil the fuel, but I got to the tick before H on the temp gauge idling with the AC on, so I really don't need to be forcing exhaust through the crossover at full temperature!

Anyone old enough to remember how they're supposed to function?

(Please don't tell me to remove it, as it serves an important driveability function. I just want it to work right).

Thanks!

[Grumpy old man]

Air flow from increased rpm's opens it further , you should be able to turn it easily when cold by hand using a light grasp .

[davepl]

Thanks GOM. So even hot it'd be normal for it to bounce around closed and open a bit at idle? It's definitely free and opens up to increased exhaust flow.

[FirstOwner69]

Bouncing is common. If it is sticking GM makes this Amazon.com: Genuine GM Fluid 88862628 Rust... lubricant. I still have some in the can I bought in the early 70s. You may want to have some on hand just in case.

[jerry moss]

you can also buy a "heat riser block" to get rid of it. it looks identical to your heat riser but has no butterfly in it. it will take longer for the truck to warm up since you are not forcing heat through the crossover in the intake BUT you never have to worry about the butterfly becoming frozen in the closed position.

[Stocker]

I got rid of mine many years ago and to be honest, I saw little to no difference. As an experiment, you could wire it open for awhile and see how it works for you.

[Grumpy old man]

It came with it stock why disable something that works ?


"Anyone old enough to remember how they're supposed to function?"

What's up with that ? I resemble that remark

[Stocker]

Originally Posted by Grumpy old man

It came with it stock why disable something that works ?

My original valve failed. I replaced it and IIRC (it's been a long time ago) I could never get the new one to seal correctly, so I removed it.

[toolboxchev]

I have one of those riser blocks that is coming out of my truck. I removed the valve years ago and never looked back.
I also use a manual choked eddy carb, no issues.

[davepl]

I'm fighting the slow attrition of warmup parts. Pretty soon people remove the heat riser, block a cross-over, remove the heat stove and pipe, or run an open element air cleaner. Then they drive it with two feet so it doesn't stall while warming up.

That's "no issues" for some but I've lived that live for decades, it's just not for me anymore! Now my days are filled either with EFI or with properly calibrated Q-jets that start, idle, run and drive like EFI.

Now it makes 330hp with headers and probably only 240hp as installed in the truck, I get it, but I have 4.88s and a steep first, so even with a muffled big block there's plenty of acceleration available... moreso than traction, anyway!

Thanks for the info on it though! I had actually expected that it would open itself once hot, as opposed to just letting exhaust through under load. I could see wiring it open seasonally maybe, but I definitely want it there for cold weather.

[lovemy71s]

Not hijacking but I got a tbi setup through kevin at performance fuel injection systems. Weld an o2 bung in the exhaust, plug in a coolant temp sensor and find a place for a map sensor, put in the new distributer that he supplies pull of the carb, bolt on the intake adapter which he makes for about any intake from what I understand, both the tbi unit on, plug everything in, after you find a place for the ecm (mine went in the glove box along with the relays, give it 12 volts and ground, plum in the fuel pump and a return (I used the vent tube on top of the tanks, and away you go, I even put remote start in my 71 gmc k1500 today.
Ps kevin is one heck of a guy to work with.