Heat riser - what's it do?

[Bob_K]

Getting ready to move to California in a few months and working on getting my car up to California emissions standard but I have a question. What does the heat riser do? I've read where some poeple yank the internals and reinstall it just to make it looks like it's there. What does this buy me?

 

[GTR1999]

It's there to aid cold weather startup. It opens when hot. Sometimes when they get old, they stick closed and give you running problems. Removing the butterfly will keep it clear and the engine will run better once it's warmed up

 

[Stallion]

As far as I know, it's only beneficial. I don't think there is any reason to take it off. A lot of guys just say the heck with it and rip off emissions parts, but a lot of them do not hurt performance at all.

 

[Bob_K]

Thanks. I wasn't sure what it did so I was considering tossing on an old used one so if it didn't work I'd rip out the internals and not care. They're not that expensive though so looks like I'll just get a new one to throw in. Now I just need to buy a complete smog system and new exhaust and California will like me!

 

[Grizzly]

If you keep it free it doesn't present a problem. What it does is force exhaust to travel from one cylinder head through the intake manifold, under the carb to the other head. The idea is to keep the manifold warm for better cold weather running. Check a car with one that is working and at first startup there is very little exhaust coming out one side. You can also see the discoloration on the intake. It is a butterfly valve that just closes the manifold and all the exhaust goes to the other side. We used to use intake gaskets with no hole so the intake manifold would be isolated and would stay as cool as possible.

 

[mvftw]

Take it off! Run dual exhaust right to the manifold. How much cold air driving do you do? I'm in NY and use my car all year and it's fine with no heat riser.

 

[Grizzly]

Take it off! Run dual exhaust right to the manifold. How much cold air driving do you do? I'm in NY and use my car all year and it's fine with no heat riser.

That's some advice for someone moving to the land of the emissions gestapo. You must have a single exhaust and cat to be legal. Probably an air pump too. Somewhere on this site is a warning about fooling with the smog controls.

If it was me, I would get a manual and check all that emissions stuff real close and do it now rather than in the rush of moving. Maybe some of our California members can give us the straight skinny on this subject.

 

[Paul T]

Hi Bob, welcome to the left coast. Listen to Grizzly above. You will be inspected for a heat riser, PCV valve, and other smog add-ons. However, if your car was manufactured for the other states without a smog pump, you will not be required to have one installed for California. You will probably have to find a good Corvette tuner to make the carb is adjusted to pass the emissions test. You have to go through this exercise every two years. I have to have my carb recalibrated each time to pass. Once you get all the pieces on it, the process will go pretty smoothly unless you have a real problem like bad rings, valves, etc. Let us know when you get settled out here and I am sure someone will direct you to a local Corvette club which will be a world of help.
Cya, Paul

 

[Bob_K]

I'm already in the process of getting all the smog equipment together. I'm rapidly getting familiar with California emissions. That's why the least I was considering was punching through it but still having it installed. As for worrying about bad rings and valves and such, I plan on rebuilding the engine soon so I shouldn't have to worry about that. I still have a few months before I go. Besides, since I'm in the military I can just keep my Vette registered in WA if I have to. Of course, I think that when I finally go back there I will get inspected too so I'm trying to plan ahead. As for the rebuild, I plan on using all California CARB EO parts, from what I've read, with AFR heads, a Comp Cams 268H cam, and a Weiand Action Plus intake, I should be making a ton more power than stock and am still 50 state legal. It really won't be holding me back too much. I think Doug Thorley Headers even makes a 50 state legal header that works with the heat riser valve (They said they made one that was 50 state, I want to double check tht the heat riser valve will still work with them). Thanks for the input.

 

[Jack]

I think Doug Thorley Headers even makes a 50 state legal header that works with the heat riser valve (They said they made one that was 50 state, I want to double check tht the heat riser valve will still work with them). Thanks for the input.

There're sort of two different things being described in this thread as "heat riser". There's the part of the system where heat (exhaust) passes from exhaust ports through an under-plenum runner ... and the part with a butterfly valve where the header pipe meets exhaust manifold (usually passenger side) and tube going up to carb. Here in south carolina we have no smog nazis yet ... so the ports are blocked and the butterfly's plate has been tossed & tube is history. Kalifornia is a horse of a different color.

 

[Big Mort]

i hope you don't mind me asking another question related to the heat riser, this seems like a good place to do it. i just got a stock exhaust system for my 1980, and it didnt come with a heat riser, and i didnt have anything like that on my last system. i plan on registering this historically, which means i dont get inspected for emissions, so all i want (due to an economical factor) is some kind of spacer or replacement that doesnt cost $100 like the heat riser valve does. could anyone help me with this problem?

 

[JohnZ]

i hope you don't mind me asking another question related to the heat riser, this seems like a good place to do it. i just got a stock exhaust system for my 1980, and it didnt come with a heat riser, and i didnt have anything like that on my last system. i plan on registering this historically, which means i dont get inspected for emissions, so all i want (due to an economical factor) is some kind of spacer or replacement that doesnt cost $100 like the heat riser valve does. could anyone help me with this problem?

See your other post.