Hi All
I need a little help identifying the manifold on my 68 396. It is a holley manifold and is stamped GM2 The issue I am having is the gasket I am using a 4 hole gasket does not cover the slot in the front of the manifold which I believe is for the smog system is that correct. Is that slot not be fully covered causing any issues? I am using a Holley 650 carb. Can anyone tell me what carb gasket I should be using?
Thanks Mike

 

That slot is called the "hot slot". There is an exhaust crossover port at the center of the manifold, below the carburetor, that flows heat from one head to the other. The holes at the ends of the hot slot connects to this port. It's not an emissions thing, it's to heat up the carburetor. The exhaust crossover is for heating up the carburetor as a whole, the hot slot is designed to prevent the carb linkage from freezing. Fine for a winter driven car, but sucks for a fair weather only car. At the very least, look into drilling, tapping, and plugging those two holes. Your carburetor will be glad you did. If your manifold isn't bolted down yet, install block off plates at the intake gasket crossover ports, or get performance aftermarket gaskets that don't have the crossover port openings.
To your question about the gasket covering the slot or not, it doesn't matter much, as long as the venturis and any vacuum passages at the base of the carb are sealed to the manifold properly.

 

If the decision is made in keeping the slot, sealing will require a heat-resistant gasket, a steel shim gasket, and a carb paper gasket.
Most parts stores will have them on display

 

Thank you for the replies. I am thinking at this point I might just change the manifold all together. Any opinions on the best aftermarket manifold to use with a street set up? Slight cam factory exhaust. Thanks

 

Depends some on what carb you want to run and what heads you have (oval port or rectangular),if you are sticking with the even bore Holley an Edelbrock performer RPM is a nice street manifold. I would guess by the cast iron intake you have you've probably got oval ports.
https://www.edelbrock.com/performer-...fold-7161.html

 

Yes they are oval port heads and I do think I will stick with the carb for now. You are actually the second person to recommend a performer manifold. Iwent to a friends shop yesterday, he builds a lot of cars and he also had the same recommendation. Thank you for your reply and great advice.

 

Glad to help,love big block 1st gens.
I built a '69 way back when I was a youngster in my early 20's,had a '68 427 in it (I'm almost 65 now).
Mine had rectangular ports 11:1 pistons and a big solid lifter Chevy L88 Vette cam so I ran an Edelbrock Torker single plane with a big Holley double pumper.
It was a bit unruly at low rpms but I had a ball with it.