C2:67 3810 Manifold Gasket?

[Gerard F.]

The 67 AIM shows a 3884575 thin stainless steel baffle on top of a 3890495 gasket to the intake manifold. I bought a carb kit and it came with a heavy duty gasket with a dogbone shaped cutout on the vacuum fitting side (it says TOP on one side).

Did the original 3890495 gasket have this same dogbone cutout? It seems to me that if you use dogbone gasket with the baffle on top, the dogbone cutout has no purpose.

Is the gasket with the dogbone intended to eliminate the stainless steel baffle or does it have something to do with heat transfer. Or do I have the wrong gasket for use with the baffle?

Jerry Fuccillo
#42179

[John H.]

Re: C2:67 3810 Manifold Gasket?

Jerry -

The dog-bone cutout in the gasket allows hot exhaust gases passing through the "hot-slot" in the carb mounting pad from the exhaust crossover passage to impinge against the stainless baffle to heat the carb baseplate for improved cold-start driveability. It also will warp and/or crack the baseplate eventually; plug the holes in the end of the "hot-slot" as shown in the photo so the carb will live a long and happy life. GM abandoned the "hot-slot" design in 1970 following a rash of engine compartment fires and a major recall.

[Gerard F.]

Re: C2:67 3810 Manifold Gasket? Thanks

John, a picture is worth a thousand words. Are those pressed in plugs, like freeze plugs, that you used.

Jerry Fuccillo

[Joe R.]

Re: C2:67 3810 Manifold Gasket?

Hi John:

Did you leave your heat riser valve in place? Is the hot slot a parallel path to the larger exhaust passage that goes across the lower level of the intake?

I'm asking these questions because I want to understand any possible consequences of plugging the hot slot. If the hot slot is just a parallel path and plugging it creates no appreciable restriction, it seems like plugging it might be a reasonable thing to do.

I do not plan on starting my engine very often when the ambient temperature is below freezing. In fact, I am more concerned about cooking the carb during hot weather conditions.

I too would like more details on how the passage can be plugged with the manifold still on the engine.

[Craig S.]

Re: C2:67 3810 Manifold Gasket?

Joe - it is as you say a parallel path...just diverting some of that exhaust up under the carb. Plug it just as John did with the small welch plugs. Even the larger passage can be plugged with intake manifold gaskets if the manifold is off and often is for warm climates and racers etc. Divorced chokes may not work nearly as quickly though.....Craig

[John H.]

Re: C2:67 3810 Manifold Gasket? Thanks

Jerry -

Those are 7/16" cup plugs in a 783 intake; castings vary, so the 7/16" plugs may not always work; you can also drill/tap for allen-head threaded plugs.

[John H.]

Re: C2:67 3810 Manifold Gasket?

Joe -

Yup, it's a parallel path with the crossover passage; plugging it doesn't affect anything else - just eliminates "cooking" your carb.

[Joe R.]

Re: C2:67 3810 Manifold Gasket?

Thanks John. I think this modification makes sense, and I'm inclined to do it now, since my carb is presently off the car (the manifold was off a couple weeks ago, but I recently reinstalled it). I'm left with two questions:

1) Exactly how would you suggest plugging the passage with the manifold on the car? From your photo I can't quite tell what you did. I suppose I could even tap the holes and install screw-in plugs, since a few metal chips in the exhaust path should not be a problem.

2) With the hot slot plugged, is it okay to leave out the stainless steel sheet that normally sits between the carb and the gasket? My guess is that I would get a better seal without the stainless part installed.

[Clem Z.]

Re: C2:67 3810 Manifold Gasket?

the chips from tapping COULD end up in the cylinder because the exhaust crossover leads into the exhaust port of the head and if the exhaust valve is open the chips COULD end up in the cylinder. just use the cup type expansion plugs

[Joe R.]

Re: C2:67 3810 Manifold Gasket?

Thanks Clem. That is a good point. Do you where I can get suitable expansion plugs? I'm not sure what vendors to try and what to ask for.

Are these plugs just smaller versions of the "freeze" plugs used in the block?

[Clem Z.]

Re: C2:67 3810 Manifold Gasket?

check the hole size with a drill bit and then go to the auto parts and check the "dorman" catalog for cup type expansion plugs because they are just smaller versions of the engine block expansion plugs.

[Joe R.]

Thanks Clem! *NM*