360 Came With A Forged Crank

RustyRatRod said

You know, a lot of people see that as a negative and talk about how more surface area of a larger min journal creates more friction. I don't buy that, because bearings and journals have clearances, with a film of oil between, so friction is minimal. In fact, I see the larger main journal as a plus, since there is more material and strength. But that's only my opinion.

I've never seen any races won or lost as a direct result from journal diameter.

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It depends on the length of the stroke and the overlap of the crank. If you have a relatively short stroke (say...3.700) you can use a smaller main bearing, still have the same overlap and not lose any strength. Then there are smaller rod bearings. The bearing weighs less, the big end weighs less, you have less mass in the counter weights...

So even at a 4 inch stroke, the 360 main bearings are bigger than they need to be, and the 2.125 Rod bearings are too big.

The reason why the 360 had bigger mains is the cast crank didn't have enough overlap with 340 sized bearings. If they would have not cheaper out and used a forged crank it would have had 340 main bearings.