Do I need a heat riser?
Race Director
Joined: Jan 2003
Posts: 17,693
Likes: 3,682
From: Central Arkansas
Unless you have blocked the heat riser passage in and out of your intake manifold (gaskets are availabe to do this), it routes exhaust through this passage from one head to the other, to warm the incoming air and carburetor. If you drive in real cold weather it will help your engine warm up faster and run a little smoother. Otherwise you can do fine without it. Warm up and your choke kicking off may be a little slower, but your intake should run a little cooler which is good for horsepower.
Dan
Dan
Race Director
Joined: Jan 2003
Posts: 17,693
Likes: 3,682
From: Central Arkansas
Same thing - that flapper valve below the manifold shuts off the pass side exhaust at idle and low RPM and forces it to pass through the heat riser passage in the head into the intake manifold. It then passes out the intake through the driver side head and out the driver side exhaust pipe. Thus the reason you use to see exhaust out one pipe only on cold mornings while idling. Now, almost no one runs a heat riser anymore - most want the slight edge on power, or the things are frozen from rust in an open position.
Dan
Dan
Drifting
Joined: Sep 2004
Posts: 1,665
Likes: 60
From: Buffalo New York
However.......
Originally Posted by 61driver
as my LT1 Build continues....do I need a heat riser? What does this do? Thanks in advance.
Ray
Ray
Last edited by Dennis Beck; Mar 20, 2006 at 09:20 PM.
Racer
Joined: Dec 2002
Posts: 437
Likes: 54
From: Cincinnati Ohio
Originally Posted by Dennis Beck
While the heat riser may not be needed for engine operation some exhaust systems are manufactured to include the dimension of the heat riser in their construction. I put a set of Allen's stainless sidepipes on my 66 and first did not include the heat riser. The passenger side pipe was just a little off until I installed a modified (took butterfly out) heat riser. I have since gone to headers and a fabricated connection to my sidepipes.
Dave
Thread Starter
Advanced
Joined: Jul 2005
Posts: 73
Likes: 0
From: Tn
Dave's Build specs?
Dave thanks for the reply. I was just searching for the build specs on your LT1 engine, but can't find it. Can you post it again when you have time. I saw one of our post refering to allens exhaust....where are they sold and what are your thoughts about it.
Thanks
Ray
Thanks
Ray
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Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Dan is correct about the closed valve routing exhaust gases from the passenger (so-called cold) side to the driver's on start-up. The passenger side muffler rots much more quickly for this reason.
My valve is welded open. The pic shows start-up last October at 28F. That was the day the car went into winter storage. Note the exhaust output is equal on both sides.
My valve is welded open. The pic shows start-up last October at 28F. That was the day the car went into winter storage. Note the exhaust output is equal on both sides.
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
Originally Posted by paul67
The passenger side muffler rots much more quickly for this reason.
one thing to keep in mind though....... when using the gaskets that close off the corssover passage in the intake which is the normal thing to do when elminating the heatriser, I have found, along with some other forum members, that it MAY create a "fluttering" sound thru the exhaust. It doesn't hurt anything but the sound is a bit annoying as it's not normal. Next winter I'll replace the intake gaskets with ones that open up the crossover passage again thru the intake manifold but still leave the heatriser off.
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Also keep in mind that if you're using an intake (stock or aftermarket) with a well for the remote choke coil and a carb that uses the remote choke setup, the choke won't work if the crossover passage is blocked. If you have an electric or hot-air tube choke, it doesn't matter. 
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
BarryK...
I think I remember you saying that you had painted your intake?? For those that did, if you open up the crossover passage I think you'll find it will discolor the paint in the area of the crossover.
I bead blasted an aluminum manifold for my '73 and clear coated it before installing it. Even after "baking" it in the oven it wasn't long before the clear in the area of the crossover had turned a caramel color. The rest of the manifold still looks fine and the clear has otherwise held up nicely over the years. If you are using the FI spacer on the right side, it's something to consider for those that do paint their intakes.
Good luck... GUSTO
I think I remember you saying that you had painted your intake?? For those that did, if you open up the crossover passage I think you'll find it will discolor the paint in the area of the crossover.
I bead blasted an aluminum manifold for my '73 and clear coated it before installing it. Even after "baking" it in the oven it wasn't long before the clear in the area of the crossover had turned a caramel color. The rest of the manifold still looks fine and the clear has otherwise held up nicely over the years. If you are using the FI spacer on the right side, it's something to consider for those that do paint their intakes.
Good luck... GUSTO
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
Gusto
no, I didn't paint the intake from my '65.
I glass beaded it than left it raw solely because of the paint turning yellowish issue from heatr.
it looks great and cleans up easily with brake cleaner this way.
no, I didn't paint the intake from my '65.
I glass beaded it than left it raw solely because of the paint turning yellowish issue from heatr.
it looks great and cleans up easily with brake cleaner this way.
