Probably other things too....but the way I understand it with the 1.53 ratio, the piston has a tendency to scrub side to side more compared to the the same crank with a longer rod. Maybe Barry or someone else smarter than me will chime in.

i know this is a  technical question  , i was just trying to figure out what way to go with my winter project and if it would be worth messing with the tall block or save it for something else,

Long rods and short pistons (from dome to bottom of skirt) with a high pin location will net slower overall piston velocity at the top and a better use of the combustion for making HP....But more prone to detination. Higher RPM? >5K +

Lower the pin and use a shorter rod and the piston speed (velocity) at the top or TDC increases and is desired for more torque(which is what a jet pump seeks) often times less prone to detination. Lower RPM? <5.5K 

Since this is not something easily tested on a dyno unless you build two engines, the info is not perfect.

The side loading is normally an issue because of the construction of the piston, shorter rods require taller pistons so "skirt slap" becomes an issue (especially with added cylinder wall clearances). Conversly, the short piston height of the long rod dealio has nothing to push against, maybe more of an issue, but I'm undecided.

As far as "the larger the better" rod ratio's, I will respecfully disagree. In the world of streetable HP, sure, but for a torque hungry jet boat, not totally true.

Hope I didn't start another torque vs. HP debate.....I don't have the energy.

I have no idea where I have the graphic of the long vs. short explanation, I will keep checking....


GT


Forgot to add...short rod = need good wall thickness and beefier rods and pins.... Less of an issue with a longer rod.

Completely agree that longer ratio is better on the street.    That is where my tiny bit of experience is.   Guess I hadn't considered boat needs would be much different, and really, are they THAT much different?

this is why i ask questions on this forum, you guy's are really helpful and the discussion doesn't turn into a snowballing argument that gets out of control like the ''other'' site. i am sure there will be more questions but, again thanks..