Heat Raiser
Thread Starter
Drifting
Joined: May 2002
Posts: 1,546
Likes: 282
From: Back in Nebraska
Heat Raiser
I’m in the process of rebuilding an old 1971 350 for my 1970 Vette. I’m to the exhaust match up now. My question is, do I need to reinstall the heat raiser on the passengers side LH between the exhaust manifold and pipe? I’m not really sure the purpose of the raiser. Can anyone shed some light on this for me?
:flag
:flag
Drifting
Joined: Apr 2003
Posts: 1,323
Likes: 2
From: Castle Hills Texas
Re: Heat Raiser (Apocolips)
The heat riser is to help with better driveability in cold weather conditions. It basically warms up your engine temp. quicker in cold weather by using the hot exhaust gasses. I believe it operates off of vacuum and the valve opens once the engine is warm enough allowing the exhaust to travel down the pipes and out the back end. I have mine on my '80 and will probably keep it even after I redo my exhaust. There are a lot of guys on here who have gotten rid of theirs and not had any problems.
Racer
Joined: Dec 2003
Posts: 263
Likes: 0
From: Kernersville Nc
Re: Heat Raiser (CVT4ME)
I found that my heat riser was broken on my 72 and laying in the closed position. It was preventing it from breathing correctly. I changed to headers since i was trying to take out the heatriser and all the bolt holes threads were rusted out on the manifold.
Eric :chevy
Eric :chevy
Drifting
Joined: Mar 2000
Posts: 1,321
Likes: 2
From: Haysville Ks
Re: Heat Raiser (Apocolips)
The 70's heat riser did not work off of vacuum, they had a coil spring on the side that would open the valve when hot. Sort of like the old coil spring in the choke of a carb.
Thread Starter
Drifting
Joined: May 2002
Posts: 1,546
Likes: 282
From: Back in Nebraska
Re: Heat Raiser (1LE)
So I gather it would be in my best interest to leave the heat raiser installed? It seems to be in working order and will clean up fairly well. Thanks to all of you that replied.
:thumbs:
:thumbs:
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Re: Heat Raiser (Apocolips)
The heat riser doesn't warm the engine up any faster than if you didn't have one. What it does is create an obstruction to the flow of exhaust gas out the passenger-side manifold. Hot exhaust from the passenger bank is forced through a small port in one of the exhaust ports on the head and through a chamber in the intake manifold. This intake chamber port opens to a stove on the bottom on the intake's plenum and is heated by the hot exhaust. The heated plenum helps to keep the fuel vaporized and prevent puddling. Continuing on...once the hot exhaust passes through the intake, it enters a port on the opposite cylinder head, passes through an exhaust port and out the driver-side exhaust manifold.
In a properly functioning heat riser, the valve will be closed to create the flow obstruction when the engine is cold (whether it is cold outside or not) and will open as the exhaust manifold heat rises to allow the coil spring to relax. One problem even with a functioning heat riser is that they tend to rot out the passenger-side exhaust pipes faster since it takes longer to burn out the condensation.
In a properly functioning heat riser, the valve will be closed to create the flow obstruction when the engine is cold (whether it is cold outside or not) and will open as the exhaust manifold heat rises to allow the coil spring to relax. One problem even with a functioning heat riser is that they tend to rot out the passenger-side exhaust pipes faster since it takes longer to burn out the condensation.
Team Owner
Joined: Sep 2000
Posts: 65,981
Likes: 15
Re: Heat Raiser (gerry72)
Gerry72,
Interesting. I had not read such a good explanation of how that thing worked. I believe if you remove the spring to the heat riser, the flapper valve is offset so that it will always be forced open when the engine is running. Am I correct?
Interesting. I had not read such a good explanation of how that thing worked. I believe if you remove the spring to the heat riser, the flapper valve is offset so that it will always be forced open when the engine is running. Am I correct?
Le Mans Master
Joined: Nov 2000
Posts: 5,210
Likes: 104
From: Fort Worth TX
St. Jude Donor '06
Father & Son St. Jude Donor '09
Re: Heat Raiser (gerry72)
The heat riser doesn't warm the engine up any faster than if you didn't have one. What it does is create an obstruction to the flow of exhaust gas out the passenger-side manifold. Hot exhaust from the passenger bank is forced through a small port in one of the exhaust ports on the head and through a chamber in the intake manifold. This intake chamber port opens to a stove on the bottom on the intake's plenum and is heated by the hot exhaust. The heated plenum helps to keep the fuel vaporized and prevent puddling. Continuing on...once the hot exhaust passes through the intake, it enters a port on the opposite cylinder head, passes through an exhaust port and out the driver-side exhaust manifold.
In a properly functioning heat riser, the valve will be closed to create the flow obstruction when the engine is cold (whether it is cold outside or not) and will open as the exhaust manifold heat rises to allow the coil spring to relax. One problem even with a functioning heat riser is that they tend to rot out the passenger-side exhaust pipes faster since it takes longer to burn out the condensation.
In a properly functioning heat riser, the valve will be closed to create the flow obstruction when the engine is cold (whether it is cold outside or not) and will open as the exhaust manifold heat rises to allow the coil spring to relax. One problem even with a functioning heat riser is that they tend to rot out the passenger-side exhaust pipes faster since it takes longer to burn out the condensation.
Another forum member, "The Andies" gave me a metal donut that replaced the heat riser and allows free flow. Engine runs better at start up and I no longer have the exhaust leak on the passenger side.
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Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Re: Heat Raiser (Apocolips)
:nono: Just one more detail here Apocolips. That thick chunk of metal makes the fit up of that side exhaust pipe correct. Without that piece the exhaust pipe on that side won’t reach or didn’t on my ’74. Just punch out that flapper and spring thing and plug the holes. Or leave the lever/weight welded on the outside as it can be considered a piece of smog equipment. :yesnod:
Drifting
Joined: Nov 2002
Posts: 1,691
Likes: 204
From: Loveland, CO
Re: Heat Raiser (gerry72)
One concern I have not seen mentioned in removing the flapper valve is the effect on your choke. Mine is what I think is called a divorced choke, which has its activation coil in a well in the intake manifold. Without the heat from the exhaust passover, I am afraid my choke will react very slowly, if at all.
Anybody have any comments on this question? I can alway convert to an electric choke, but that would look funny on a tripower.
Anybody have any comments on this question? I can alway convert to an electric choke, but that would look funny on a tripower.
Instructor
Joined: Dec 2002
Posts: 242
Likes: 0
From: Port Orchard Washington
Re: Heat Raiser (rponfick)
Yes, removal of the valve will not allow exhaust to pass under the well for the choke on your year engine, causing a longer period of time for the choke spring to become heated and leaving your choke on longer.
Every oil change, manipulate the lever weight to ensure smooth operation and lubricate with a small amount of high temp. anti-sieze annually and the valve will last another twenty years.
Every oil change, manipulate the lever weight to ensure smooth operation and lubricate with a small amount of high temp. anti-sieze annually and the valve will last another twenty years.
Melting Slicks
Joined: Feb 2003
Posts: 2,330
Likes: 6
From: Long Island NY
Re: Heat Raiser (Missileman)
:iagree: That's why I had true duals installed and removed the heat riser. I also had the carb rebuilt with electric choke and blocked off the xover. :D This is the to fly...
