Bellhousing #621

[Michael S.]

Was the #621 used on early '66 Corvette Big Blocks?

[John M.]

Re: Bellhousing #621

I have only seen the 444 on 66 bigblock cars...John

[Joe L.]

Re: Bellhousing #621

John and Michael-----

Yes, all 1966 Corvette big blocks used the GM casting #3872444. Very early 1967 Corvettes may have used it as well.

The 3899621 was used for most, if not all, of 1967 for all big blocks except L-88. It was also used for all 68-74 big block applications except 68-69 L-88/ZL-1.

From a FUNCTIONAL perspective, the 3872444 and the 3899621 are equivalent and may be interchanged for all Corvette applications originally using either. The 3899621 superceded the 3972444 for SERVICE.

[Steve Antonucci]

Re: Bellhousing #621

Joe,

I once heard that the '621 bell housing was not used on L-88's and ZL-1's.

For the ZL-1 Camaro's, I have heard that they used the 3858403 bell housing.
Why was this the case? Was the same SB bell housing also used for the L-88's?

I have always wondered why GM would use the SB bell housing for these special
BB engines. Obviously, it had to have something to do with a smaller clutch
assembly ( weight ? ). I believe the SB used a 10.40 clutch while the BB used
an 11.00 clutch.

Steve

[Joe L.]

Re: Bellhousing #621

Steve-----

Yes, as I mentioned in my previous response, the 3899621 was not used for L-88 or ZL-1. The GM #3858403 was used for all L-88 and ZL-1, including those ZL-1's installed in Camaros. It was also used for most, if not all, 1965 Corvettes with L-78 (the GM #3840383 MAY also have been used for some of these. It's identical to the 3858403 except for a feature irrelevant in a Corvette application).

The GM #3858403 is not a "small block bellhousing". It was used for a lot of small blocks, but there is nothing that "ties it" to those engines. It's simply a bellhousing designed for use with Chevrolet block bolt pattern, small block or big block, and 12-3/4" flywheel size.

The 1967-69 L-88 as well as 1965 Corvette with L-78 were the only Corvette big block applications which ever used a 12-3/4" flywheel. However, since they did use that size flywheel, they also used the GM #3858403 (or, 3840383) bellhousing which were the only available bellhousings in the GM "parts bin" designed for the intended application.