72 LT-1 Holley carb to intake nsulator/spacer

[Ed H.]

I am getting my 72 LT-1 ready for Fight Judging. I have been looking for an OE reproduction carburetor insulator or NOS insulator/spacer GM part number 3999259 or possibly GM part number 6271056-7 for the Holley carburetor (although I think that is the CA emissions version with heat shield). I would appreciate any suggestions on where I might be able to locate this part. I currently have a 1/4" separation spacer for functional equivalence installed and the engine runs fine.

[Joe L.]

Re: 72 LT-1 Holley carb to intake nsulator/spacer

I am getting my 72 LT-1 ready for Fight Judging. I have been looking for an OE reproduction carburetor insulator or NOS insulator/spacer GM part number 3999259 or possibly GM part number 6271056-7 for the Holley carburetor (although I think that is the CA emissions version with heat shield). I would appreciate any suggestions on where I might be able to locate this part. I currently have a 1/4" separation spacer for functional equivalence installed and the engine runs fine.

Ed-------

First of all, the GM #6271056 and 6271057 were not gaskets with heat shield as used for EEC. In fact, for 1972 no such gaskets were used. The 6271056 and 6271057 may once have been available in SERVICE but I cannot find that they were ever cataloged for a Corvette application.

The GM #3999259 is quite difficult to find. However, I believe it is simply an insulating gasket of about 1/4" thickness with plastic, torque limiting reinforcements at the corner stud holes. In general, Dr. Rebuild has the most correct reproductions of carburetor base gaskets (as well as most other gaskets and many other parts).

[Ed H.]

Re: 72 LT-1 Holley carb to intake nsulator/spacer

Thank you for the clarification Joe. You are right about Dr. Rebuild as a good source for this part unfortunately they no longer carry them in inventory or can source from their suppliers.

[Paul C.]

Re: 72 LT-1 Holley carb to intake nsulator/spacer

I am looking for the holley carb/intake gasket for 1971 LT-1. I tried DrRebuild--no luck. Anyone know where can purchase one. Thank you.

[Joe L.]

Re: 72 LT-1 Holley carb to intake nsulator/spacer

I am looking for the holley carb/intake gasket for 1971 LT-1. I tried DrRebuild--no luck. Anyone know where can purchase one. Thank you.

Paul-------


The original carb gasket for 1971 LT-1 was GM #3989390. This gasket was discontinued from SERVICE in July, 1972 and replaced by GM #3999198 which was discontinued more than 20 years ago. I've never found a GM #3989390 but I do have a 3999198 [not for sale]. I don't know how the 3999198 differed from the 3989390. However, I expect the differences were minor. I think you should be able to find a more-or-less similar gasket in the aftermarket. The original gaskets have no nylon torque-limiting inserts at the bolt holes. Both gaskets are 1971-ONLY gaskets.

Be aware of gaskets with nylon torque limiting inserts at the bolt holes. These gaskets are both good and bad. The good is that the inserts ensure that the exact compression of the gasket is achieved. The bad is that this makes the gaskets a "one shot only" kind of thing. In other words, they really need to be replaced each time the carb is removed and re-installed.

Below some photos of an NOS GM #3999198.

DSCN0991.jpgDSCN0992.jpgDSCN2769.jpgDSCN2770.jpg

[Paul C.]

Re: 72 LT-1 Holley carb to intake nsulator/spacer

Joe:

Thank you for the pictures. Can you tell me exactly how thick it is and what type of material is it made out of--soft spongy or hard dense material? What are the dimensions of the square opening?

[Joe L.]

Re: 72 LT-1 Holley carb to intake nsulator/spacer

Joe:

Thank you for the pictures. Can you tell me exactly how thick it is and what type of material is it made out of--soft spongy or hard dense material? What are the dimensions of the square opening?

Paul-------


The gasket is right at 9/32" thick. It is a cellulosic material and is quite firm although it is slightly compressible. This is from my previous notes and recollection. I can't get to the gasket right now to measure the opening.