[DavidNJ]

What Anthony said.

This has been discussed extensively on various engine forums. If there is no displacement limit, engine builders stroke (and bore) as far possible. It always makes more power. Which accelerates faster.

The inertia in the rotating assembly is minimal, something on the order of 4-6lb-ft even from a big block. At 6500rpm we are talking maybe 5-10hp. The flywheel/clutch assembly may bave 2-3 times the inertia.

Yes, if displacement is fixed, a big bore/short stroke will allow bigger valves for better breathing and some less stress on the rod cap and bolts. However, if you are in the rev range of street Cobra, those stresses aren't a limiting issue. And for a street Cobra (or any Cobra not in a organized racing class), displacement isn't limited.

For the record, NASCAR and F1 are both displacement and bore limited by the rules. And 4.5 and larger are standard big block Chevy stroke sizes. Here, we are keeping the bore constant and the discussion is between more stroke and displacement vs less stroke and less displacement.

For the Cobra the big thing seems to be cost and availablity. 4.25 cranks and matching pistons for BBC rods are a (relatively standard item). 4.375 and 4.5 seem to be custom items.