Rod ratio vs reversion
 

I have been doing a lot of reading on rod ratios and to be honest its enough to make you dizzy. my machinist suggested I use a longer rod on my build to help with piston side loading. In my reading I found it changes the torque curve and piston speeds and dwells at different points in the cycle, unless I'm not reading things correctly a longer rod might help fend off water reversion?.

longer rod, slower in changing direction (at top at bottom) and faster in the middle.. but overlap is still overlap and that pulse in the exhaust wave (similar to intake wave) is where the risk of reversion comes from... closing the exhaust valve a bit sooner will help with reversion but will hurt the HP IMO PUT A BLOWER ON IT!!! cause ya can't suck and blow at the same time!!!

Don't worry about it. Total cubes, CR, heads, cam, exhaust and induction are what affect your power and where you make it.

I had a girlfriend that can prove you wrong on that one. ;)

OP - it sounds like you're just purging your brain of info overload, but I've never heard an engine builder bother to take stroke into consideration about reversion as of all of the components to consider on that issue that aspect is minimal.

The longer rod will increase dwell time at TDC and BDC, and will reduce reversion affects. Cam intake and exhaust overlap will indicate the potential for reversion but without piston movement the flow just doesn't reverse on its own accord. The longer dwell allows the exhaust to flow a bit further down the exit before piston movement on the down stroke begins to reverse the flow on the exhaust valve closing event.

In a nut shell a longer rod/stroke ration can dampen reversion.

Would you agree though within the usable stroke/cylinder length like in a 9.8 deck block that a 6.385 rod with a piston pin height of lets say 1.270 would be better for longevity, ie ring seal than any benefits of running like a 6.535 rod with 1.120 pin height? I see in drag racing guys will use these 1.080 to 1.120 pin heights but I assume they are going in motor thats ran 100th the time for re-ring vs a offshore boat? Thanks, Smitty

a drag car only lives is spurts never really put to the endurance test like the life of a marine engine... 1.270 is ok but 1.120 NEVER... at least you'd never see my name attached to it... I'm sure others will also speak to this as well

if you wanted to build a killer and reliable 522... 4.560 bore w a 6.535 rod and a 4.0" stroke will give you a good compression ht of 1.255 putting it .010 in the hole if all is std

would be higher RPM friendly

The longer rod will increase piston dwell time at TDC and will shorten dwell at BDC..

Short-rod should have the shortest dwell at TDC and the longest dwell at BDC.

Exactly I would never use that short compression height to try to get a even longer rod in