Posted by Brian in Oregon on Wednesday, October 10, 2001 at 6:40PM :
In Reply to: MORE on the Big-Bad 300 posted by gary on Wednesday, October 10, 2001 at 11:00AM :
Have you noticed that the 251 family has a block that is about two inches longer than the 230 family?
The reason for this is that the rods are offset in the 230 and straight in the 251 (as well as allowing a larger bore).
By offset, if you help up a 230 rod and looked at it from the side, you'd see that if an imaginary line ran from the wrist pin down the beam of the rod, it would not go through the center of the rod bearing. The rod bearing is offset. This means that is is more susceptible to loading problems particularly at higher RPM's. Spun bearings could be a consequence of high cylinder pressure loading or detonation combined with higher RPM's. The 251 would be able to take more pounding as the rod journal is not offset. To accomplish this, the block had to be stretched, which also allows larger cylinder bores.
In my opinion, if I were to try and run a 230 at higher RPM's and "hot rod" it, I'd really be looking into pinning the rod bearings. That would help prevent spinning a bearing (but it would not prevent pounding and perhaps galling).
Frankly, I'd rather run a 251 or 265 if I needed to push a flathead past 2800 rpm (which is a max speed of 45 mph in an M37 with a 230 and 5.83 gears with 900x16 tires).
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