Chevy & GM Engines
CHEVY V8: When it comes to bellhousing bolt patterns, the small & big block Chevys are the same. (This is known as the 90 degree bolt pattern). These engines use a dowel pin alignment. The stock starter bolts to the bottom of the block except on some early blocks like the 265. (Note: These early blocks, in which the starter bolts to the bellhousing, should not be used for conversions). The flywheel can either be 153 tooth measuring 12-3/4” in diameter, or 168 tooth measuring 14” in diameter. The 1985 & earlier flywheels are not interchangeable with the 1986 & later flywheels due to a change on the flywheel crank bolt pattern and balancing. If you are using a stock GM bellhousing, make sure you have proper clearance for the flywheel. For the proper starter, GM used two different bolt patterns on the bottom of the block. The straight bolt pattern is normally used with the 153T flywheel, and the offset or staggered starter bolt pattern is normally used with the 168T flywheel. Many Chevy blocks today offer both starter bolt patterns on the block. Some of our conversion bellhousings require a special GM starter nose cone. If your stock starter is interfering with our bellhousing, you may need to grind on the bellhousing a bit or purchase a hi-torque starter which does not have a nose cone. Warning: Do not use one of our full conversion bellhousings with a diesel engine. The starter will not fit the bellhousing pocket on our bellhousings.
The oil pans on Chevy blocks have gone through a few changes. 1985 & earlier blocks are all the same except the dipstick access is either on the driver’s side or passenger side. In 1986, GM changed their gasket design to a one piece rear main seal. The earlier style oil pans will not fit the newer blocks. The computer controlled blocks in the ‘90s added oil level sensors. The pans that we manufacture do not have provisions for this sensor.
Most GM blocks used a triangular motor mount bolt pattern. Our conversion mounts all utilize this most common mounting configuration. Some late ‘90s blocks have varied from this bolt pattern. Please confirm that the block your converting has this triangular mounting pattern. LS1 blocks and Vortec Gen. III V8 blocks use a square bolt pattern for the motor mount. We offer a full selection of conversion mounts for these blocks. GM also changed the crank flange stickout location on the LS1 and Vortec Generation III V8 blocks. This crank is recessed .400” closer in than any other stock Chevy block. When these blocks are used in a conversion, the torque converter or clutch components will need to be adjusted. LT1, LT4, ZZ4, LS1, and Vortec blocks all use angle port heads which are not compatible with most of our header systems. We offer some specialized headers for these blocks. These blocks also require a steam release port on the radiator. The radiator we offer can be ordered with this steam release provision.
CHEVY 90 degree V6: This block can either be the 3.8 (229) or 4.3 V6. These engines are identical to the Chevy V8 application with reference to bellhousing, starter, and flywheel. The oil pan has year differences like the Chevy V8 except with the 1997 & newer aluminum oil pan. Vehicles requiring oil pan modifications should not use this block. Motor mounts are also the same as the Chevy V8 with the exception of the location of the triangular bolt pattern in reference to the back of the block. The mount is approximately 4-1/2” closer to the backside of the block.
CHEVY 60 degree V6: This is the 2.8L V6 used in S10s and Jeep Cherokees. This bellhousing bolt pattern is completely different than the 90 degree Chevy bolt pattern. GM automatics that have this bolt pattern will not bolt to the 90 degree blocks. In 1996, GM introduced a stock engine replacement known as the 3.4L.
BUICK V6: Buick used two different bolt patterns like the engines listed above. The 225, 231, and 3.8L (rear wheel drive vehicle) all used the standard Buick bolt pattern for which we offer motor mounts, bellhousings, and adapters. Engine blocks like the 3.8L transverse (front wheel drive vehicle) have the same bolt pattern as the Chevy 2.8L V6. We do not offer adapters or motor mounts for the Buick aluminum 215 block.