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Replacing gaskets on the passenger side exhaust manifold when I realized there was an exhaust heater riser? My c3 is 1976, and I thought the heater riser only go to 1974s. There was nothing inside it, do I need to buy the plate that goes inside? Or can I just buy the gaskets for it and leave it be? ( Yes I know its upside down in the picture)
My 1980 had that POS, and it was stuck in the closed position(frickin GRRRRRRR). Glad yours was shelled-out. Unless you are replacing the manifolds with headers, leave it be.
Might get by with eliminating what is left of the heat riser. I did on my 77, the pipe is only raised a little higher.
exactly what i did on my 79.. and used same donut gasket.. i did however later purchase the spacer to get the exhaust a little further from starter.. i got it on ebay and had to drill out the holes a little fyi...
The heat riser is designed to more quickly warm up your intake manifold and carb to ease cold starts. With it functioning properly your car will need to utilize less choke and therefore will run rich for a shorter period of time during each and every cold start. The colder the engine is, the greater the benefit. The warmer it is, the less advantage is realized.
The heat riser does for your intake and carb what your engine thermostat does for your engine block and heads.
The heat riser is designed to more quickly warm up your intake manifold and carb to ease cold starts. With it functioning properly your car will need to utilize less choke and therefore will run rich for a shorter period of time during each and every cold start. The colder the engine is, the greater the benefit. The warmer it is, the less advantage is realized.
The heat riser does for your intake and carb what your engine thermostat does for your engine block and heads.
There's a reason the LS engine design eliminated both coolant and exhaust crossovers in the intake manifold.
If that heat riser fails closed, at best your car will run terribly.
There's a reason the LS engine design eliminated both coolant and exhaust crossovers in the intake manifold.
Beginning in the eighties, on some carbureted cars, GM began using electronic EFE modules, which eliminated the possibility of a mechanical heat riser failure. This was all prior to the advent of ubiquitous fuel injection in automobiles.
But I believe the OP is asking about a Seventies era Chevy engine in a '76 C3. So, let's work with what we have. His '76 C3, like my '79, was designed with an EFE (Early Fuel Evaporation) system. This particular system utilizes a mechanical heat riser rather than an electronic device.
The EFE system aids with vaporization of fuel in cold conditions, as well as to reduce exhaust emissions. However, heat risers were originally installed on cars solely for warming up the carb, not for emissions related concerns. That came later, as it became clear that warm engines run cleaner then cold engines.
Originally Posted by Bikespace
If that heat riser fails closed, at best your car will run terribly.
I agree.
The primary component in the EFE system in question is a vacuum actuated Heat Riser mounted below the right-side exhaust manifold.
Noteworthy, is Chevy designed the EFE system so that in the event of a vacuum failure, the heat riser will fail wide open. That is a good idea.
Nevertheless, that leaves the possibility of a mechanical failure of the heat riser (becomes stuck in the closed position), which can happen, and that would cause the engine to struggle at higher RPM. Not good. Therefore, if that were to happen, replace the failed heat riser, like any other failed exhaust part on the car that provides a benefit.
In the meantime, with a functioning EFE system, the C3 will run better sooner over thousands of cold startups. This is especially true for all those times it is cold or very cold out.
I have hot air choke stock setup. Removing the riser valve doubled my choke high idle time from maybe 3 minutes to 6 (1500/900 warm rpm) on a sub freezing day, and less difference when warmer.
drives fine but on high idle as you take off for a longer time.
i still have the manifold exhaust crossover original. I would consider an electric choke conversion at that point if needed but i don’t know how much it would add to choke opening time.
i have a manual but i could see it being bigger pain with auto potentially.
No snow, rain, salt, i drive year round.
My 75 had one, i think, we just wired it in the open position, after the Hooker headers and side pipes we went to the factory side exhaust and needed the spacers to make it fit.
So, just do away with it, just saying.
Exhaust Heater Riser
