Poly Engine what was good/bad about it and why is the LA better?

cudamark said
Yes, same outside diameter to match the inside diameter of a flywheel, but, the inside diameter is smaller on the 273 for the early 904 converter button. And as I mentioned, the cranks that came in a manual trans car were finish machined for a pilot bushing. Most automatic cranks weren't. With a 318 crank, that's no big deal because a Magnum pilot bearing will work fine in the big register. With a 273 unfinished pilot hole, that bearing won't fit, so, you either have to machine the register hole bigger, or, hone the pilot hole smooth and machine down a bushing to fit. In the times where I swapped cranks between a 273 and 318, the balance was never way off, but, also, never close enough for me. I always rebalance an engine anyway when doing a rebuild, so, not an issue with me. For up to 5000 RPM, sure, probably not an issue, but, higher RPM's with new aftermarket and oversized parts along with machining everything, I feel much better when everything is properly balanced.

Thx for the early 273 crank register info. As for the pilot hole often being unmachined in an automatic trans crank, that's pretty much true for any of them isn't it? I know my Dad and I had to get a 440 automatic crank machined for a pilot bushing so we could run a four speed behind it.

Edit: that was long before Magnum pilot bearings existed. I see what you're saying, with a later 318 crank you can use the Magnum pilot bearing, but you can't with the early 273 unless you machine the pilot register bigger.