Preparing to reinstall my rebuilt engine (L71) this weekend and noticed that the right exhaust manifold does not have a heat riser, or valve assembly, like on my previous small block cars. I checked the Assembly Manual and there is one shown is Section 6 but not again towards the rear where the L71 engine is depicted. The manifold has the correct part number and apppropriate date. It also has what I would call a spacer measuring 1 1/8" thick but there is no flap, or valve. So should a big block have the valve and if so, what happens when/if there is no valve as in my case?
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Re: 67 427 Heat Riser
Someone likely replaced the heat riser valve with the "FI spacer" way back when. If you are not concerned with loss of judging points or commonly drive the car in subfreezing weather, leave the spacer installed.
Duke -
Re: 67 427 Heat Riser
Tom-----
I agree with Duke. All 1967 Corvettes were originally equipped with a heat riser valve EXCEPT L-88. So, either the car is an original L-88 or someone previously replaced the heat riser with the spacer used for pre 66 FI and 67-69 L-88 applications. Most likely, it's a case of replacement.
The primary reasons to remove and replace a heat riser with the spacer are as follows:
1) VASTLY extend right side muffler service life;
2) A MUST DO if the heat riser CROSSOVER in the intake manifold is blocked via gaskets or plates(if you go back to a heat riser you MUST check to be sure the crossover is not blocked;
3) To eliminate, once-and-for-all, the infernal rattling of heat riser valves.
Without the heat riser, your choke might not operate as well. In fact, what may occur is the choke will remain on for a longer period. However, enough heat should eventually get through the cross-over to sufficiently warm the stove. If the heat cross-over is blocked (via gaskets, plates, etc.), the choke, if installed, will never be off. So, if your choke works, at all, you can be pretty confident that the cross-over is not blocked.In Appreciation of John HinckleyComment
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