Finally ready for a new prop

nola mike

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Apr 22, 2009
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Previously had a 3.7l 170hp, replaced last year with a 4.3l that should be good for 220hp. Was hoping for a big jump in performance, which unfortunately didn't happen. Dry weight listed at 1150# on the sales flyer fwiw. Had run an alu 3 blade 23p on the old motor, transferred it to the new. With me on board it would hit around 49 mph @4600 rpm. I swapped an aluminum 3 blade 21p turning point prop. Unfortunately didn't seem to make too much difference on pulling me up on a slalom ski (though my wife isn't sure if she floored it trying to get me up :rolleyes: ). Hitting 30 mph @ 3300 rpm vs 3100 previously, as expected. Top speed with me and 2 kids (150#) was 46-47 mph at 4700 rpm. That's probably closer to where I want to be in the rpm range. I definitely am looking for something with more low end, and my cruising speed is typically 30 mph. Don't care too much about top speed. I also think that the extra 200# or so of engine in the stern is more detrimental than I'd thought it would be. Seems to not be able to trim up as much. Thinking a 4 blade 21p would be what I'm looking for (19 I think would be under?). Suggestions? Probably will at least initially look for aluminum, I'm never sure how much difference ss makes...
 

QBhoy

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Mar 10, 2016
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8,348
What kind of boat is this. Some going for a 3.7 as she was previously. Must be a fast hull she has. What 4.3 did you put in her ? Was she a built motor with fancy parts to see 220hp or was she an mpi or brand new quicksilver unit carb ? Those are the only 2 4.3 I know of that can make 220hp. Both vortec.
 

nola mike

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Joined
Apr 22, 2009
Messages
5,414
What kind of boat is this. Some going for a 3.7 as she was previously. Must be a fast hull she has. What 4.3 did you put in her ? Was she a built motor with fancy parts to see 220hp or was she an mpi or brand new quicksilver unit carb ? Those are the only 2 4.3 I know of that can make 220hp. Both vortec.
My boat just sunk (see my thread in the mercruiser section), so the prop's on indefinite hold. But it's an '01 block (vortec, roller lifters, cam) with a 4bbl carb. Michigan motorz lists the same engine as 225 at the crank. Dang, definitely not feeling that.
 

Scott06

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Apr 20, 2014
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My boat just sunk (see my thread in the mercruiser section), so the prop's on indefinite hold. But it's an '01 block (vortec, roller lifters, cam) with a 4bbl carb. Michigan motorz lists the same engine as 225 at the crank. Dang, definitely not feeling that.
I know your efforts are on revfloating and reviving your boat now but Assuming you can get it dewatered and running - try a michigan vortex 4 blade I think based on your numbers an 18" would probably plant you about 5 k lightly loaded and help pulling up.
 

QBhoy

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Mar 10, 2016
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8,348
Hi. Is your tachometer now changed its setting from 4 cylinder to 6 ?
 
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