Chevy 261 offset crank with 292 rods and caddy pistons

The problem on the 4 main bearing 6's is almost always harmonics. The cranks are stout and the journals are huge, so if you keep the RPM's low they can stand all the power you can cram in the cylinders. However, you can't run at high RPMs for long without some major work to the balancing and the harmonic damper. 292's can spin faster RPM than 261's because the 3 extra bearings keep the crank from flexing around, and the rods and pistons are lighter. It takes major work to a 261 to even approach the stock 292 redline. I think if you turbocharged a 261 and kept the RPMs low you would blow the head off the block or the bottoms out of the pistons before you would break the crank.

The GMC 302 has basically the same crank design as the 235/261, but it makes more power because of the extra bore, better combustion chamber, and better rod ratio. The 302 has a 4" bore and stroke.

 

A 292 already has a notched cam for the stock stroke. There really isn't any more room to stroke it.