Heat Riser vs No Heat Riser
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Heat riser systems have been on cars much longer than emissions stuff. But, as you live in EPAland, one never knows. However, if you open the riser valve and remove the valve from the shaft...then reassemble it, how would they ever know? From the outside it would appear the same and operate the same. It just wouldn't block exhaust flow from going down the pipe. And, it probably wouldn't be cold enough for it to close, anyway.
Last edited by 7T1vette; Jan 8, 2017 at 02:31 PM.
Racer
Joined: Mar 2016
Posts: 470
Likes: 31
From: Melbourne Victoria
Heat riser systems have been on cars much longer than emissions stuff. But, as you live in EPAland, one never knows. However, if you open the riser valve and remove the valve from the shaft...then reassemble it, how would they ever know? From the outside it would appear the same and operate the same. It just wouldn't block exhaust flow from going down the pipe. And, it probably wouldn't be cold enough for it to close, anyway.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
I should not experiment like this but I tend to. A normal heat riser tends to work fine if lubricated once a year or so. Years ago GM had a special spray to do that job. Nowadays I guess PB Blaster is the equivalent.
Last edited by Paul L; Jan 8, 2017 at 07:24 PM.
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Without the riser the stock choke takes about twice as long (or more) to fully release so with a divorced choke you need to lengthen the rod (make a new rod) to the carb by almost a half inch to get it to release sooner. If you want to block off the manifold you MUST replace the riser with an open spacer or gutted riser or the exhaust will be blocked on the passenger side. If you need a choke and the manifold is blocked you have to go to an aftermarket divorced electric choke.
Last edited by CanadaGrant; Jan 8, 2017 at 10:46 PM.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Hi Paul. The spacer has the same triangular flat on one side shape as the end of the exhaust manifold so that the ears on the cast exhaust manifold sit flat up against it (gasket between) and don't break off when tightened down or with heat cycles.
Without the riser the stock choke takes about twice as long (or more) to fully release so with a divorced choke you need to lengthen the rod (make a new rod) to the carb by almost a half inch to get it to release sooner. If you want to block off the manifold you MUST replace the riser with an open spacer or gutted riser or the exhaust will be blocked on the passenger side. If you need a choke and the manifold is blocked you have to go to an aftermarket divorced electric choke.
Without the riser the stock choke takes about twice as long (or more) to fully release so with a divorced choke you need to lengthen the rod (make a new rod) to the carb by almost a half inch to get it to release sooner. If you want to block off the manifold you MUST replace the riser with an open spacer or gutted riser or the exhaust will be blocked on the passenger side. If you need a choke and the manifold is blocked you have to go to an aftermarket divorced electric choke.
Last edited by Paul L; Jan 9, 2017 at 03:48 PM.
7th Gear
Joined: Nov 2012
Posts: 7
Likes: 0
Question to add to this thread - Will the -`74 spacers work on the 1975? It's also got a 2" manifold output. I have seen certain vendors list this part up through the early `80s, and others not.
Getting ready to order a dual exhaust from CC, so the question is at least timely for me. . .
Getting ready to order a dual exhaust from CC, so the question is at least timely for me. . .
Melting Slicks
Joined: May 2012
Posts: 2,192
Likes: 344
From: Allenton Wisconsin
Question to add to this thread - Will the -`74 spacers work on the 1975? It's also got a 2" manifold output. I have seen certain vendors list this part up through the early `80s, and others not.
Getting ready to order a dual exhaust from CC, so the question is at least timely for me. . .
Getting ready to order a dual exhaust from CC, so the question is at least timely for me. . .
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028