I was reading the 70-72 judges manual page 61, paragraph 4-5. What is the heat-insulating insert for the carburetor bolt? Any pictures of this out there? Also, I have been looking for the black nut with built-in washer that bolts the carb to the intake. This is a 1/4" NF bolt and I cant seem to find this in black oxide as referenced in the manual.
70 LT1 Intake / Holley carb stud.
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Re: 70 LT1 Intake / Holley carb stud.
I was reading the 70-72 judges manual page 61, paragraph 4-5. What is the heat-insulating insert for the carburetor bolt? Any pictures of this out there? Also, I have been looking for the black nut with built-in washer that bolts the carb to the intake. This is a 1/4" NF bolt and I cant seem to find this in black oxide as referenced in the manual.
The heat insulating insert, GM #3967466, was used only for 1970 Corvettes with Rochester Q-Jet AND NA-9 California emissions. It was not used for any other applications on Corvettes. It is a very difficult part to find so, if you have an LT-1, be thankful that you don't need one.
The carb retaining nuts were 5/16-24, not 1/4". The original nut, GM #3967486, was discontinued without supercession in May, 1986. However, I THINK a currently available GM #1359887 will come pretty close to configuration and finish of the original.In Appreciation of John Hinckley- Top
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Re: 70 LT1 Intake / Holley carb stud.
Terry------
The Holley carbed 1970 LT-1 did not use the insulators whether NA-9, or not. The GM #3967466 insulators were designed for use on the front BOLTS for Q-Jets; they were not designed for or used on the rear throttle body retaing STUDS for Q-Jets. The Holley carb used studs for all 4 throttle body mounting positions and, consequently, no insulators were necessary or used.In Appreciation of John Hinckley- Top
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Re: 70 LT1 Intake / Holley carb stud.
One thing to keep in mind about these insulators: On a Rochester Q-Jet the forward to-manifold retaining bolts pass through the air horn, float bowl, and throttle body components of the carburetor. I believe the purpose of the insulators was to reduce the amount of heat transferred from the manifold through the bolt to the air horn and throat bowl. In doing so, the evaporative emissions would be, theoretically, lessened. Evaporative emissions control was the whole purpose of the NA-9 system.
For NA-9 systems the heat transferred to the throttle body (and from there potentially to the rest of the carb) was mainly reduced by the insulator gasket used between the carb and the manifold. Apparently, it was determined that very little extra heat would be transferred through the studs to the throttle body so no insulators were deemed necessary. As I mentioned above, no insulators were used for the rear mounting positions of the Q-Jet or all 4 mounting positions of Holley carbs since these positions retained only the throttle body to the manifold.
An interesting side-note is this: for the 1971 model year and thereafter, the NA-9 system was incorporated into the "standard emissions equipment" supplied on all Corvettes. However, the insulators used for the forward bolt mounting positions for Q-Jets were eliminated. Improved insulating gaskets between the carburetor and manifold were used, though.
The idiotic carb "heat slot" used for all 1968-69 Q-Jet applications as well as many prior year cast iron manifold applications was thankfully eliminated for the 1970 model year and, by itself, resulted in a major reduction in heat transmitted to the carburetor. However, the manifolds all still used the exhaust heat cross-over passage necessary with heat riser valve systems and external chokes. So, a lot of heat was still present on the carb flange of the manifold, potentially transferred to the carburetor.In Appreciation of John Hinckley- Top
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