List of GM bellhousing patterns

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The following is a list of GM bellhousing patterns. Though General Motors has manufactured many different engines, it has kept variance in the bell housing patterns to a relative minimum.

Chevrolet V8 pattern[edit]

This was so named because it began with Chevrolet's V8 engines.

GM metric pattern[edit]

Also called the GM small corporate pattern and the S10 pattern

This pattern has a distinctive odd-sided hexagonal shape. Rear wheel drive applications have the starter mounted on the right side of the block (when viewed from the flywheel) and on the opposite side of the block compared to front wheel drive installations. The 2.2l S10/Sonoma had the starter located in the same position as front wheel drive cars. A rear wheel drive bellhousing is displayed at right, and the integrated front wheel drive bellhousing is displayed at the lower right (in this case, as a part of the GM 6T70 Transmission).

Northstar pattern[edit]

Nearly identical to the GM small corporate/metric pattern, except that the starter is located between the cylinder banks, and the lower right bolt hole is moved outward by roughly one inch. Being nearly identical, it too has the distinctive odd-sided hexagonal shape. These engines can be fitted in rear wheel drive vehicles with the right bellhousing and are used in hot rods, kit cars, sand rails and late model engine swaps.

Atlas pattern[edit]

Atlas family engines use a unique bellhousing pattern which no other GM motors share.

Pre 1964 Buick and Rover V-8 Round pattern[edit]

Buick, Oldsmobile, Pontiac (BOP) V8 pattern[edit]

BOP V8 Pattern

Four bolt holes and two locator pins are common to the Chevrolet, and B-O-P patterns. Some transmissions, most notably the TH200-4R, take advantage of this by integrating both specifications into a "universal" bolt pattern casting.

Cadillac V8 pattern, pre-1967[edit]

Early Cadillacs manufactured before 1965 used a "round top" bellhousing very similar to early Buicks; around 1965, the bellhousing pattern was revised until the BOP bolt pattern was adopted in 1968.

GM 4-cylinder pattern[edit]

GM Ecotec 4-cylinder pattern[edit]

An example of this pattern can be seen to the right.

GM Ecotec Generation III pattern[edit]

The completely re-engineered Generation III Ecotec includes a new uniquely shaped bellhousing pattern.[1]

GM High Feature V6 pattern[edit]

  • Cadilac 2.8


  1. ^ "LTG FWD | performance-engines". 2020-06-23. Archived from the original on 2020-06-23. Retrieved 2020-06-23.