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What is the difference between an off-center block and an on-center block. I believe the 86-87 motors are even fire on-center blocks and the stage 1 3.8 block is an off-center block?

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Originally posted by 231rush:
What is the difference between an off-center block and an on-center block. I believe the 86-87 motors are even fire on-center blocks and the stage 1 3.8 block is an off-center block?

Not quite. All production motors are off center. This refers to the centerline of the rod in the bore; off-center motors have a rod that's offset approximately .110" from the bore centerline. The early stage motors (both 3.8 and 4.1) are off center; when horsepower levels began increasing the bore centerlines were revised to eliminate this offset and the rod problems it caused. Stage blocks from about mid 1987-on are on-center. The on center blocks require unique rods and a new or modified intake.

Basically any motor that's post 1977 is even fire; the 30 degree offset rod journals are the identifier. Some Stage motors were run in odd-fire configuration; the cranks are easy to identify as they have a common rod pin for 2 rods like a V8 crank.

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Orange Park, FL
various cars, some running
 
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