What about a 4 5/8 arm 615ci

Thank you Haxby for sharing some of your knowledge and technical info.. feels like threads of old

A couple of years ago we worked with Bob Madara on a set of carbed 572's dry sump engines and made 804 HP at 6100 RPM. They have good idle and run on 93 octane.

You can get a 10.4 block from dart and put a little longer rod in to help with piston speed.

10.4 block?can you explain how rod length affects piston speed?

Longer rod lets the piston dwell at the top and bottom of the stroke for a longer period of time. Doesn't change the speed in between. If I was to build 632 for a marine application I would want the longest rod possible. Dart does run off some 10.4 blocks usually have to wait to get them.

Rod length affects the maximum piston speed, and can have effects on how the engine breathes from a airflow standpoint. Can also effect the amount of ignition timing needed based on dwell times.

Rod length is almost irrelevant, I'd prefer to have a decent piston than the longest rod possible.

Doesn't a short rod put more side pressure on the piston and block causing ring failure, don't some engine builders call it a bad rod to stroke ratio.

I dont know if it will cause ring failure but your piston skirts will take a beating.