Exhaust Heat Valve
Drifting
Joined: Oct 2010
Posts: 1,972
Likes: 6
From: Chester Virginia
My 76 now true duals has no heat valve, no A.I.R. pump, etc. The heat valve was supposedly I read once put there to put some heat back into the intake to preheat the air to produce less pollutants until the engine was hot then the spring opened it back up.
I'd think it was just another piece of crap to coke the power out of the engine and is well rid of if the above explanation is accurate. Either way, my 76 L48 runs just fine without it!
I'd think it was just another piece of crap to coke the power out of the engine and is well rid of if the above explanation is accurate. Either way, my 76 L48 runs just fine without it!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The heat riser valve is there to help heat the carb/choke in cold weather, so that the engine will warm and drop the choke sooner. It had nothing to do with emissions. If you won't be using the car in really cold weather, there is no need to keep it. You can then put block-off plates in the heat riser channel on the intake. That will reduce unnecessary heating of the carb.
Melting Slicks
Joined: Nov 2010
Posts: 3,363
Likes: 32
From: Bowtie, Pennsyltucky
St. Jude Donor '13-'14-'15,'21
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Drifting
Joined: Oct 2010
Posts: 1,972
Likes: 6
From: Chester Virginia
epa
The heat riser valve is there to help heat the carb/choke in cold weather, so that the engine will warm and drop the choke sooner. It had nothing to do with emissions. If you won't be using the car in really cold weather, there is no need to keep it. You can then put block-off plates in the heat riser channel on the intake. That will reduce unnecessary heating of the carb.
At least from the reading I've done so I'd want to expand the context of what you said above as it all had to do with combustion and in that generation emissions.
Lance P.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
The heat riser valve is there to help heat the carb/choke in cold weather, so that the engine will warm and drop the choke sooner. It had nothing to do with emissions. If you won't be using the car in really cold weather, there is no need to keep it. You can then put block-off plates in the heat riser channel on the intake. That will reduce unnecessary heating of the carb.
I once removed the valve from a year round beater I had back when I believed that everything GM did was evil and robbed power. All I got for my trouble was a car that wouldn't idle worth a da*m for the first twenty minutes or so during the winter.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Heat risers have been on cars for much longer than the EPA has been in existence. They may have an effect on reducing emissions (compared to the same car but with no heat riser), but that is coincidental. Of course, the manufacturer would put some 'spin' on it to impress the Feds that they were "working hard to reduce emissions"...
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
The heat riser valve (called Early Fuel Evaporization valve by GM) is there to do just that. Gasoline needs heat to vapourize it so it will burn. Liquids don't burn - their vapour must mix with oxygen in the air to burn. When the engine is 'cold', the gasoline is still partially liquid and doesn't burn as well (a pseudo-lean condition) as when it gets heat from the hot intake manifold. So, the choke mixture has to be richer and stay active longer than without it.
Usually, when you change the exhaust system (and remove the EFE) you adjust the choke slightly w/o knowing you are partly compensating for that.
Here we go again ..... Years ago GM did a series of tests and found a 1/2" hole in an otherwise completely blocked intake crossover system made the mixture burn better than a completely blocked intake crossover system. That was with a carb though, not MPFI. AT WOT it is inconsequential.
Usually, when you change the exhaust system (and remove the EFE) you adjust the choke slightly w/o knowing you are partly compensating for that.
Here we go again ..... Years ago GM did a series of tests and found a 1/2" hole in an otherwise completely blocked intake crossover system made the mixture burn better than a completely blocked intake crossover system. That was with a carb though, not MPFI. AT WOT it is inconsequential.
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
If you live in Wisconsin or some other cold climate, you will not be happy with how the engine runs on startup for the first 5 or 10 minutes in November, December, January, February or March...
I tried adding some weight to the iron counter weight on my heat riser so it would open sooner and stay open longer. I drilled and tapped the counterweight, and added a stud and some heavy nuts on the end. Looked ugly, but it worked fine.
I tried adding some weight to the iron counter weight on my heat riser so it would open sooner and stay open longer. I drilled and tapped the counterweight, and added a stud and some heavy nuts on the end. Looked ugly, but it worked fine.
Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
If you live in Wisconsin or some other cold climate, you will not be happy with how the engine runs on startup for the first 5 or 10 minutes in November, December, January, February or March...
I tried adding some weight to the iron counter weight on my heat riser so it would open sooner and stay open longer. I drilled and tapped the counterweight, and added a stud and some heavy nuts on the end. Looked ugly, but it worked fine.
I tried adding some weight to the iron counter weight on my heat riser so it would open sooner and stay open longer. I drilled and tapped the counterweight, and added a stud and some heavy nuts on the end. Looked ugly, but it worked fine.
