So last summer I noticed the port motor was lagging but really only at high rpms close to wide open. I did a leakdown and compression test on all 16 cylinders and were all even at 165 (which is where the dynamic compression calculator put it at) and 5 to 6% leakdown. Engines ran fine. I pulled them and dyno them and they are same top end power, with the port actually being a bit stronger down low. I checked cam timing and some how the starboard motor is 2 degrees retarded which I'Lloyd address.

Is it possible the tranny is slipping under heavy load letting the starboard side spin up and lug the port side? The fluid isn't burnt but I didn't really hold them wot for long because if this. I checked trim, they are even and tried other props,same deal. The top speed dropped a few mph too.

Not possible, any slippage causes almost immediate failure and the oil would be burnt.

Check tune, I struggled to figure this out for a full season, for some reason on dyno engines were identical, in the boat both engines ran richer, but port was always more rich, took out some jet and they evened out, I have widebands though to watch air fuel ratios in the boat, I would look at something like that..

I have widebands as well don't remember the exact readings but they were a little different. Want to say high 11s one and very low 12s the other wide open. Carbs are brand new 850 marine quick fuels.

I think I'm going to switch engines side to side when I reinstall

I have no explaination for it but a half point of A/F fixed mine... the port was always richer even when the same on dyno, cleared that and issue went away...

Every once in about 3 blue moons you will see a trans apply a little reverse while going forward from either a valve body issue and or warped clutch plates.will cause lower than normal wot on affected motor ,stalling if bad enough, and generally way high tranny temps and eventual temp alarm sounding.

Im with MBAM. The clutches are either locked, or they arent. If they arent, they will burn up in no time, and you wouldnt even be able to get on plane.

Dont forget too, that if your cam timing was retarded 2* from where you installed it from chain stretch, if that was the case, your ignition timing would also have retarded from your initial setting

Ok thanks all, just wanted to rule out that possibility. The fluid is clean and they don't turn hard or spin the props in neutral so I don't think clutches are warped.

And that trans cooler isnt getting extra hot in fwd gear.. Thats the bingo clue for that rare elusive type of trans issue .
Before it goes critical mass.