Key Features
- Cast aluminum reproduction of legendary GM #3899621 bellhousing
- Direct bolt-up to Muncie 4-speed pattern transmissions - no adapters required
- 168-tooth flywheel configuration with 4-5/8" pilot bore
- Accepts up to 11" clutch diameter
- Compatible with Muncie, Saginaw, Borg-Warner T10, TREMEC TKX, and TKO transmissions
- Factory-like attachment using stock or Holley oil pan
- Designed for both hydraulic and mechanical clutch fork linkage
- Lightweight aluminum construction - non-SFI rated
- Fits Chevy small block and big block engines
Description
When you're swapping to a modern TREMEC transmission or rebuilding with a classic Muncie, the last thing you want is adapter-stacking and fitment headaches. This cast aluminum bellhousing is a faithful reproduction of the legendary GM #3899621 - the heavy-duty 11" clutch housing that GM used across Corvettes, Camaros, Chevelles, and full-size Chevys from the mid-'60s through the early '80s. It bolts directly to any Chevy small block or big block with no adapters required.
The 621 bellhousing features the 168-tooth flywheel configuration with a 4-5/8" center bore, originally designed for GM's heavy-duty 11" clutch applications. The transmission side accepts any gearbox with the standard GM Muncie 4-speed bolt pattern - including the original Muncie M20/M21/M22, Saginaw, Borg-Warner T10, and modern TREMEC TKX and TKO transmissions. This makes it the ideal foundation for upgrading from a 3 or 4-speed manual or automatic to a modern 5 or 6-speed TREMEC.
The design accommodates both hydraulic and mechanical clutch fork systems, giving you flexibility in your release setup. Factory-like attachment using stock or Holley oil pans ensures clean integration in GM cars and trucks, as well as swap applications into other chassis. This non-SFI rated aluminum casting is a lower-cost alternative for street builds under 500 hp that don't require steel SFI certification. Made in the USA.
Kit Includes
- Cast aluminum 621-style bellhousing with GM #3899621 casting number
- Bellhousing alignment procedure instruction sheet
- Lifetime technical support
Note: This bellhousing does not include mounting hardware or fork pivot stud. For pivot stud, see item# MD-401-6026.