Quadrajet
Thread Starter
Racer
Joined: Sep 2017
Posts: 338
Likes: 56
Quadrajet
Hello. My question has to do with the heat baffle/shim and base gasket on my car. The car is a 69, 350c.i, stock manifold and carb # 7029207. Some vendors seem to list and sell slightly different baffle, gaskets for carb to manifold. Should both the heat baffle and the gasket have a hole between the secondary cut outs? What is the purpose of this hole and lastly the proper placement is it manifold, gasket, heat baffle then carburetor? Thanks in advance for your help.
Le Mans Master
Joined: Aug 2005
Posts: 6,541
Likes: 1,975
From: Temple Terrace Florida
On my 68 small block, I installed Dorman plugs in each hole to prevent the exhaust gas from going under the carb. I paid about $.50 each for the plugs at my local NAPA store. I also used an aluminum heat baffle as well. GM did this for a few years to aid in warming the engine in the winter. With todays gas, it can contribute to vapor lock. Jerry
Thread Starter
Racer
Joined: Sep 2017
Posts: 338
Likes: 56
I did a search and found an old posting by Lars that helped explain things. He mentioned about putting a gasket on both sides of the metal heat shield to help prevent heat transfer from the metal heat shield to bottom of the carburetor and create a better seal than the metal shield to the bottom of the carburetor would have. This seldom gets mentioned but seems to make sense and if recommended by Lars, can't go wrong.
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
If you have the smiley face manifold, you need at least 3 gaskets in this order. Manifold, high temp combination steel/fiber gasket, stainless steel block off plate/gasket, regular paper gasket, carb.
You can also add insulator or larger heat shield into the mix. I use a aftermarket aluminum plate that helps dissipate heat after you park the car, to minimize the gas boiling. Seems to help.
You can also add insulator or larger heat shield into the mix. I use a aftermarket aluminum plate that helps dissipate heat after you park the car, to minimize the gas boiling. Seems to help.
Advanced
Joined: Apr 2020
Posts: 80
Likes: 14
From: Ont, Canada
The double gasket is not necessary, but may not hurt. In the picture of the manifold I posted, the arrows point to where you can tap and plug the exhaust passage that comes to the bottom of the carb. These cars don't get driven in dead cold winter anyways. I would tap and plug.
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
The double gasket assures that you have a leak proof seal between the metal plate and the carb base and provide a little insulation. Where else in the vacuum system do you have a metal to metal, no gasket or sealer joint?? Putting the carb directly on the metal shield wouldn't leak much, but probably wouldn't be 100% sealed. I also put a 1/4" phenolic spacer and a aluminum heat dissipation plate below the carb, to help with hot restarts.
On MY car, in southern california, when I blocked off the cross over at the head/intake manifold juncture, the choke would not get hot and release for a very long time. Didn't work well. But I did install plugs later and the choke now works ok.
Overall, once the car get hot, the heat still travels through my stock aluminum manifold, through the carb mounting bolts, etc., to the carb. EVERYTHING under my hood eventually heats up to 200?? deg. MY major issue seemed to be getting the choke to work correctly. The car seems to run the same, when fully hot, weather the cross over is blocked or not, because the carb eventually gets hot anyway.
On MY car, in southern california, when I blocked off the cross over at the head/intake manifold juncture, the choke would not get hot and release for a very long time. Didn't work well. But I did install plugs later and the choke now works ok.
Overall, once the car get hot, the heat still travels through my stock aluminum manifold, through the carb mounting bolts, etc., to the carb. EVERYTHING under my hood eventually heats up to 200?? deg. MY major issue seemed to be getting the choke to work correctly. The car seems to run the same, when fully hot, weather the cross over is blocked or not, because the carb eventually gets hot anyway.
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