PontiacGroup.com
Main Bearings and Pontiacs
3/4 grooved main bearings are a must for all high performance applications using 3" main journal blocks (326-400ci) and the IAI/II 3" main aftermarket blocks. The advantage is you get the oiling of a fully grooved bearing with the load handling capability of a half grooved unit. This is not as critical on the 3 1/4" main blocks (421,428 and 455ci) since the cranks are cross drilled and oil is delivered every 180 degrees. But naturally there is no harm in using 3/4 grooved bearings here either.
UPDATE: The new AllPontiac/BOP forged cranks us straight shot oiling and is a great improvement over the factory style oil delivery. Both the 3" & 3 1/4" main journal cranks would benefit with these 3/4 grooved bearings
