Swapped lower unit and LOST A LOTof SPEED!!

[mbecke2]

I SUCCESSFULLY put a lower unit from 110 johnson v4 crossflow on my 140 looper and lost 12 mph. I know the gear ratios are slightly different but come on should I really have lost 12 MPH??? I used to go 43 and now Im topping out at 31 WOT. Takes a while to plane out also. Is this expected or am I missing something?? I am runnin a 19 pitch and getting about 5000rpm at WOT if i trim up all the way. I was told to decrease pitch but wouldnt I lose more speed?? Does this make any sense?? I just dont think I can deal with going 31mph with a 140 looper on a 17ft boat, that just aint right. The motor sounds good and I think the timing is good and the carbs are opening all the way and getting full amount of fuel. Any suggestions?

 

[Mas]

Re: Swapped lower unit and LOST A LOTof SPEED!!

I do not know aout the gears...but is it the same prop? Maybe the prop/hub is slipping?

Mas

 

[kenmyfam]

Re: Swapped lower unit and LOST A LOTof SPEED!!

What was your WOT RPM previously before changing the lower unit ???

 

[emdsapmgr]

Re: Swapped lower unit and LOST A LOTof SPEED!!

That's a lot of speed to lose-25%. You need to count the revolutions of the gearbox to see what gear ratio you had on the 140 stock lower unit vs what you have now. The 110's were all a 13:26 ratio. In 1985, the 140 ratio was 13:28 and in 1989 the ratio was 12:27 for the long shaft. Shaft length also makes a difference. In one of the early 140 looper years, (maybe the 1985) they used V6 gearcases (and V6 props) with different gearsets. I would agree to drop the pitch on the prop. That engine is designed to turn up to 6000 rpm, and at 5000, you are lugging it. Probably why the holeshot if poor, to.