steel baffle under carb

[Gary #41345]

Ecklers doesn't have it listed and Mid America only shows it listed for the 63-65 base engine??? Was this steel baffle used on the 1966 base 300 hp engine?

[John H.]

Re: steel baffle under carb

Gary -

Yes, it was; the '66-'67 base engines had a Holley, and the '63-'65 base engines had a Carter WCFB - they use different baffles. Suggest you plug the two holes at the ends of the "hot-slot" in the intake manifold before installing the gasket, baffle, and carb.

[Gary #41345]

Re: steel baffle under carb

I've seen this mentioned here a few times John, what's the condition that occurs if you don't plug those two holes?

[Joe L.]

Re: steel baffle under carb

Gary-----

Among other things, if you don't plug the holes, the extra heat that the carb is exposed to will cause its deterioration in a much quicker time frame. Especially of concern is the warpage caused for throttle bodies and float bowls. I ALWAYS eliminate this carb heat groove by plugging the holes. Actually, after you plug the holes, the carb stainless steel baffle plate is really no longer necessary. However, you can still install it.

[Gary #41345]

Re: steel baffle under carb

I see Joe.....I wonder about those "among other things" although the heat issue you speak of is probably the worse possible thing...was this considered a design/engineering flaw in its time..and what's the best material to use to plug those holes? any kind of epoxy?

[Joe L.]

Re: steel baffle under carb

Gary------

It wasn't considered a "design flaw", per se. However, this system caused GM some huge problems. It was completely abandoned after 1969. No 1970 or later Chevrolet applications utilize it.

You can't use epoxy to seal the holes; it won't take that kind of heat. Probably the best and easiest way to plug the holes is to simply drive cup shaped plugs into the holes. These are like "mini-freeze plugs" and can be purchased at most auto parts stores. I believe the size is 3/8".

Alternatively, you can tap the holes for NPT allen head plugs.

[Kevin M.]

Like this

Be sure to wire open the heat riser? at the manifold connection too.

Kevin

[Joe L.]

Re: Like this

Kevin-----

If this is the only mod performed, it's not necessary to wire open the heat riser (although it might be a good thing to do for other reasons). If the crossover passages are blocked at the interface of the manifold and cylinder head vis blocked type gaskets, then the heat riser MUST be wired open or, better yet, permanently removed and replaced with a spacer.

[Kevin M.]

Re: Like this

Joe,

What is pictured is the only mod I know of, but I was advised to do the wire thing. Glad it doesn't really matter, when I had my muffler and pipe installed they left it unwired, didn't notice right away.

Kevin

[Joe L.]

Re: Like this

Kevin-----

Plugging the holes as you have pictured just eliminates, basically, a "side channel" for the exhaust gases that pass through the intake manifold crossover. The primary exhaust gas passageway remains. By plugging the holes pictured, though, the main detrimental effect of the crossover is eliminated.

The passage can be completely closed by using intake manifold gaskets with blocked heat crossover openings. When this is done, the heat riser valve must be securely blocked open or eliminated. However, if the heat cross-over passage is completely blocked, the operation of the divorced style choke used on all 1966-74 Corvettes will be greatly compromised.

[Timothy B.]

Re: steel baffle under carb

Gary, Picture shows the heat shield from my 67 just before it was changed, also plugged the small holes under the carburetor.

[Timothy B.]

Re: steel baffle under carb

This is the other side of shield, looks like exhaust gas was starting to enter intake as shown from soot trail.

[Gary #41345]

Re: steel baffle under carb

I dropped the car off at a carb pro this morning and asked him to plag the holes prior to installing the new carb and he thinks that the holes don't have to be plugged based on his experiences. I informed him of the general agreement that takes place here that they should be plugged...... should I insist he plug them? regardless of him belief? He is a Corvette guy too..has owned many.

[Timothy B.]

Re: steel baffle under carb

Gary,
I am not a carburetor expert but I'm glad mine are plugged. The purpose of the heat groove is to keep ice from forming in the carburetor around the idle transfer slots and butterflys on cool humid days durning warm up. I still use the original stack of gasket and heat shield installed but manifold is plugged. I guess it's your choice, with the holes plugged the carburetor is no where near as hot as before and I like that.

[Joe L.]

Re: steel baffle under carb

Gary-----

I don't know what his "experiences" are. I just don't see how anyone could have any POSITIVE experience with this system. I can imagine how they might not UNDERSTAND what the NEGATIVE consequences of the system are, though. Otherwise, what he MAY be referring to is that this system sometimes carbon-plugs on its own which, effectively, eliminates it. However, I would not rely on that being the way it is; it's too tenuous. It's way too easy to just plug them with drive plugs and be CERTAIN the system is "dead" once-and-for-all.