Determine right prop

[kekray13]

Hi, owner of a 1988 chapperal 204 W/A. Orginally powered by a 1988 Evinrude 175 hp w/ an aluminum prop 14x19. I believe my WOT then was approx 4800rpm w/ a speed of 39mph. This year replaced that engine w/ a 1994 Evinrude 175 hp w/ a SS prop 15x17. WOT is now 4600rpm. Boat weight dry is approx 2000lb. Any suggestions in fitting the new engine w/ the correct prop? I don't know what the OMC WOT range is for this new engine.

 

[Dhadley]

Re: Determine right prop

I would have bet that going from a crossflow to a 60* looper you'd have picked up rpm even with the same prop. That's how it's been every time I did it. But you even went to a smaller prop and got less rpm. Are you sure the newer motor is running as it should?

The extreme low rpm also has me concerned. At 4600 you're looking for over 1000 rpm. If it was all prop you'd have to drop 5 - 6" in pitch. Something isn't right with this picture.

I'd even allow for 300 rpm to be (possibly) gained in set up - assuming the older motor wasn't set up to the max either.

Let's make sure the tach is set right (on position 6) and if so, let's check out the motor. make sure the linkages are all going full open, the timing is right and it's hittin on all 6.

 

[kekray13]

Re: Determine right prop

Thanks, I'll check as suggested. However, to let you know I did test run this engine last year on the sellers boat. I think it tacked out at 5400rpm and ran well. Compression was b/t 98-105 on all 6. After purchase I fogged and winterized. The tach reads 1100 at start and then comes down to 900 after warm up. I'll re-check the linkage.