1972 LT-1 Heat riser Valve

[STEVE MUELLER]

Dear Sir:

I have a question on a valve that is on the passenger side of my car. There seems to be some kind of (possibly a heat riser valve that is wired up) Does this attach to someting in connection with A.I.R. system or is temp activated. If it is a valve does any one know where to get it and or a part#.

Steve

[Juliet P.]

Re: 1972 LT-1 Heat riser Valve

I'm not a Sir, but I'll answer your question anyways. :P

Yes that's the heat riser valve. I just changed my wired one also, (1970) after soaking the bolts with penetrating oil twice a day for a week. You need to loosen some of the exhaust holders so that you can swing the exhaust out of the way to get the riser in & out & the flanges cleaned up. Stuff a rag in the exhaust so that you don't get rust flakes in there when wire brushing it clean.

I purchased my replacement from Zip Products for about $35 US. I don't have the part number handy. It allows the exhaust gas to go up through the manifold to prewarm the maifold (and the carb somewhat too I think) for cold starting conditions. Yours is probably wired so that it never passes the gas through the manifold just like mine was. You can check the exhaust when starting the car on a cold day and if only the driver tail pipe is letting out exhaust then it's wired so it doesn't activate itself.

Part numbers for everything on your car is pictured in the AIM. How to fix it, build it, service it and rebuild components are in the Service Manual & Chassis Overhaul Manuals. Some of these NCRS sells, or you can find them on eBay or in the catalogs. If you get them through NCRS and you're a member you get a discount and you help support this information board. :D Of course the AIM may not have the current service part numbers, but just about any Chevy dealer can it look up and get the service number from the build part number... at least my local Chevy dealer has been able to do that for the parts I've searched so far... ~Juliet


Juliet's 1970 Corvette

[Joe L.]

Re: 1972 LT-1 Heat riser Valve

Steve-----

The valve is both temperature and exhaust flow controlled. At low exhaust temperatures(i.e. during cold start warm-up) and low exhaust flow conditions, the valve is closed, directing exhaust from the right side cylinder bank through the intake manifold crossover and exhausting on the left side exhaust pipe, for the reasons that Juliet described in her response.

When exhaust temperature increases or if exhaust pressure significantly increases when the valve is otherwise closed, the valve opens. There is a bi-metallic coiled spring which controls the temperature actuation of the valve and the counterweighted mainshaft arm controls the need for valve opening at higher exhaust pressure. Higher exhaust pressures would otherwise overwhelm the volumetric gas-carrying capacity of the intake manifold crossover passage.

You can purchase the valve for your car at any GM dealer under GM #362652 for a current list price of $32.25. These valves are also available in the aftermarket, but configurations may vary slightly from the GM and many are "imported".