427 Heat Riser Spacer
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Burning Brakes
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From: Ct
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427 Heat Riser Spacer
Pulled off the sidepipes for spring cleaning and got a good look at the heat riser flap inside the pass exhaust manifold collector - looks allfully restrictive -I was thinking of running this summer with just a spacer for even exhaust flow. Besides a bit of cold start roughness - any reason why I would not want to do this ??
PS - I don't know why a poll feature appears - this is not a poll - just a question
[Modified by 66BBCoupe, 1:24 AM 3/22/2003]
[Modified by 66BBCoupe, 1:52 AM 3/22/2003]
PS - I don't know why a poll feature appears - this is not a poll - just a question
[Modified by 66BBCoupe, 1:24 AM 3/22/2003]
[Modified by 66BBCoupe, 1:52 AM 3/22/2003]
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
Re: 427 Heat Riser Spacer (66BBCoupe)
I don't think you'll notice any difference in warm up performance, especially if you only drive the car in mild weather. Even with the spacer, if you don't block the passages at the inlet manifold/head interface, exhaust gas will still be able to migrate through the passage and keep the base of the manifold warm. The colder the weather, the more the heat riser helps with warm-up driveability, but most of us don't drive our vintage Corvettes in the dead of winter anymore.
There's just no other way to describe the heat riser valve but "PIA". I wired mine open on my L-76 SWC in '68 after it rotted out the RH OEM muffler, and when I rebuilt the engine, I replaced it with the FI spacer. The decision was a no-brainer.
I had very bad success blocking the heat riser passage, which I tried once. The engine would stumble from a dead stop start until it had been running for at least 20 minutes in mild weather. You really need some heat under the carb to provide good low speed driveability. One thing that might be worth trying is just blocking one side of the passage. This would still allow exhaust gas to migrate up the dead end passage and keep the base of the manifold warm, but blocking both sides is definitely not the way to go for a street driven car.
Duke
There's just no other way to describe the heat riser valve but "PIA". I wired mine open on my L-76 SWC in '68 after it rotted out the RH OEM muffler, and when I rebuilt the engine, I replaced it with the FI spacer. The decision was a no-brainer.
I had very bad success blocking the heat riser passage, which I tried once. The engine would stumble from a dead stop start until it had been running for at least 20 minutes in mild weather. You really need some heat under the carb to provide good low speed driveability. One thing that might be worth trying is just blocking one side of the passage. This would still allow exhaust gas to migrate up the dead end passage and keep the base of the manifold warm, but blocking both sides is definitely not the way to go for a street driven car.
Duke
Drifting
Joined: Jun 2000
Posts: 1,596
Likes: 52
From: Southern NJ
C2 of Year Finalist (stock) 2019
Re: 427 Heat Riser Spacer (66BBCoupe)
Peter -- I have actually cut out the butterfly on my heat riser. I threaded the remaining shaft on the weight side and installed a nut to hold it in place so it wont fall out. Looks exactly stock. I have no problem whatsoever with warm up. While you have the sidepipes off make sure the extensions that go between the exhaust manifold and the sidepipe are in place. And of course -- new doughnuts.
good luck
john lolli
good luck
john lolli
Melting Slicks
Joined: Aug 2000
Posts: 3,077
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From: The Garden Spot of the Garden State
Re: 427 Heat Riser Spacer (66BBCoupe)
..yup, disconneted mnie and then finally removed the butterfly altogether and capped the ends with short threaded allen head studs...
...agree with john lolli
...agree with john lolli
