Let's say, for comparison sake, that we were comparing 2 engines, both were measured at approximately 502 cid. One motor is a 4.25 stroke and 4.34 bore, the other is a 4.00 stroke 4.47 bore. All other components are the same.

What's your opinion on these motors?
One better for lighter boats?
Or they both the same... a cube is a cube no mater how you measure it?
Are they going to have different aspiration needs?

I'm curious if the runner velocities do anything weird on the large bore/short stroke combos, and how bad piston speed gets on the opposite.

Wow , long time since I've seen your name.

This subject has been rehashed many times. Some people believe more stroke is better, some more bore, and others say cid is cid.

None of the less, will be a good subject for winter time.

How does the 8.1 run compared to the 8.2, guessing the larger bore would breath better and make more power across the board depending on cam, intake, heads and exhaust.

I would say Bore for unshrouding reasons, but I also would say if you are building engine and machining parts why not spend a few bucks more and do both? to me I would rather have the gen^ block with bigger bore for future builds worse case...

Stroke give you mechanical leverage. (rod center is farther from the crank center) but also increases rotational load. If I had to do just one for the most improved performance, I would do stroke for a heavier boat.
I would go the shorter stroke and bigger bore in lighter boat to possibly increase rpm response (reduced rotational load).

OR, a couple of beers later, the first crank might be in the second motor, rod length and wristpin height allowing!

Kinda like puttin money on a drunken bar brawl with two guys who have the same strength however are a foot difference in height. Lol.

All bs aside first thing that comes to mind is the longer the stroke would have a broader power band with more torque at lower rpm while the shorter stroke making its peak hp and torque at a higher rpm. Not sure if one vs the other would ultimately have skirt wear prior to the other giving same hours of use. Another thought is the longer stroke would also increase swept volume in the cylinder but personally only see advantages if was to be turbocharged etc. long jevity one vs the other???

Good question. While you are at it hopefully someone explains why Mercury always uses the 557 cu in platform.

what about aspiration? Does anyone think there could be a difference in need for aspiration? Would the shorter stroke benefit more from a larger volume runner, and the longer stroke benefit more with a slightly smaller runner volume? I'm thinking it would benefit more from the velocity, but the difference is prolly more theoretical than physically realistic.