Hi, I have question regarding the gasket between carb and intake. I have a 68 430 intake and a 73 Q-jet from a BBB 455. Which gasket should I use now, the 68 or 73 style gasket? My part supplier said they are different. Thanks in advance Stefan
You are probably looking for the one that suits the manifold--especially if you've got the older style manifold that has the exposed exhaust crossover. Chevy's last year for that was '69; I know Buick had it in the mid-60's but I don't know when they stopped. Be sure the base gasket has the hard plastic inserts were the bolt holes are; too many Q-jets are ruined by people who overtighten the front bolts and then the gasket crushes. The overtorquing/crushed gasket leads to warped carbs.
You will need to actually plug/fill with epoxy the exhaust heat crossover under the front of the carb, as the later carb baseplate is not wide enough to cover it. Even if you get the right gasket, there will be nothing holding it down over the ends of the crossover.
Hm, I'm not sure which crossover do you mean. I have pluged the heat pipes in the heads, but did nothing with the intake. Here is a pic of my intake (primed).
The U-shaped trench that wraps around in front of the primaries is connected to the exhaust heat crossover. If you have blocked the exhaust crossover in the heads you should be OK.
Nicholas, I see what you mean! But this little trench is solid cast iron. No way for exhaust gases to pass in any case. Even if I haven't plugged the heads, there should be no problem with exhaust gas leakage. Or is the heat itself the problem? Stefan
1. Heat is a problem. The original installation will have used a very thin steel heat shield shaped like the base gasket to protect the carb from the blowtorch effect of having the exhaust gas in direct contact with the carb. Either you deliberately block off that passage from the exhaust crossover; or you deliberately block the exhaust crossover; or you better have that heat shield in addition to the base gasket. The engine will run very poorly without the shield, as you'll have exhaust gas pulled into the fuel/air mix, too. 2. You understand that the exhaust gas flows through that trench from one side of the engine to the other side--right? Unless it's deliberately plugged, exhaust gas WILL be in that trench. Whichever side of the engine has the heat riser (EFE) valve in the exhaust system will be the supply side; exhaust gas will flow from that side to the opposite side through that trench unless it's blocked.
Schurkey, thank's a lot for that good explanation! Sorry guys, I found another thread, where someone else mentioned two holes connecting the trench with the heat cross over. I didn't know that and there is nothing about that in my service manual. Obviously the previous owner of my car had plugged these holes. ou: The search engine didn't work for me, because I haven't added the keyword cross over. After that I found a ton of threads about this common issue. However, problem solved. :beers2: Thanks Stefan
