Accurate Horsepower Figures

Scott06

Admiral
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Apr 20, 2014
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The Venturi is larger, as the carb has a higher Air Flow. A 5.7 needs a bigger Carb than a 5 liter. Rejetting is not going to make it a bigger carb
I didnt mean to rejet- both the 5.0 and 5.7 have the same jetting. this is the file I meant to attach with those specs. Not sure if the venturi is any different other than the holes for accelerator pump nozzles, which could be drilled out.
 

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Joined
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If you have too much pitch that would be the case, but usually to get on plane relatively quickly I'm 2/3-3/4 open throttle, then pull back once on plane. Your WOT RPM will be key- if you are on the low side of your range say 4400 rpm go down to a 19" pitch.

The carb was set up for a 5.0 - the jetting and power valve is the same as in attached file. The venturi is different as it has larger accelerator pump discharge holes on a 5.7. Not to over complicate things but might help to drill out the accelerator pump discharge holes or move the pump arm lever to the closest hole to get a bigger shot (2nd attachment).
The linkage is in the middle "B" hole.
 
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Okay, so I was able to take her out this weekend. First some more info......three weeks ago I hit something at slow speed pulling up to an unfamiliar launch area to drop some passengers at their campground. No dock, just pulling up to the beach near the ramp. Took a good sized chunk out of one blade, maybe the size of a half dollar. I just needed to go a few more miles back to where we put in, so I took it slow.......surprisingly I didn't feel any vibration and it seemed to run normal. Pulled the prop took it to a local shop, they said it would be a week to get it fixed so I picked up a Black Diamond prop at West Marine.......same size 14.25 x 21P. Figured I would just keep the repaired prop on board as a spare.

So with the boat loaded as usual, nearly a full tank of fuel, one passenger, bay pretty smooth and no wind I was surprised at how much different this new prop performed.....

We tried several runs, using full throttle, motor turning 3600 rpms out of the hole, on plane in 5.2 seconds, pulling back on throttle and cruising at 3800 rpms. Moving to WOT, quickly reaching 4800 and then creeping up to 4900 - 5000 rpms at 50 mph. Tried a few more runs to see how much less throttle it needed to get on plane. I would estimate that 3/4 throttle wouldn't get me there but somewhere between 3/4 and less than full throttle would give me the same results....on plane in just over 5 seconds, which is waaaaayyyyy better than the old prop. Night and day!!!
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,428
Okay, so I was able to take her out this weekend. First some more info......three weeks ago I hit something at slow speed pulling up to an unfamiliar launch area to drop some passengers at their campground. No dock, just pulling up to the beach near the ramp. Took a good sized chunk out of one blade, maybe the size of a half dollar. I just needed to go a few more miles back to where we put in, so I took it slow.......surprisingly I didn't feel any vibration and it seemed to run normal. Pulled the prop took it to a local shop, they said it would be a week to get it fixed so I picked up a Black Diamond prop at West Marine.......same size 14.25 x 21P. Figured I would just keep the repaired prop on board as a spare.

So with the boat loaded as usual, nearly a full tank of fuel, one passenger, bay pretty smooth and no wind I was surprised at how much different this new prop performed.....

We tried several runs, using full throttle, motor turning 3600 rpms out of the hole, on plane in 5.2 seconds, pulling back on throttle and cruising at 3800 rpms. Moving to WOT, quickly reaching 4800 and then creeping up to 4900 - 5000 rpms at 50 mph. Tried a few more runs to see how much less throttle it needed to get on plane. I would estimate that 3/4 throttle wouldn't get me there but somewhere between 3/4 and less than full throttle would give me the same results....on plane in just over 5 seconds, which is waaaaayyyyy better than the old prop. Night and day!!!
Sounds like a winner. The old prop must have been messed up as black max and black diamond are same prop under Mercury and Quicksilver labels respectively.

if you are hitting that upper end of rpm range you are spot on. Just watch rpms when lightly loaded.
 
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Sounds like a winner. The old prop must have been messed up as black max and black diamond are same prop under Mercury and Quicksilver labels respectively.

if you are hitting that upper end of rpm range you are spot on. Just watch rpms when lightly loaded.
That's good information.......both props sitting beside each other on the bench looked identical except the Black Max didn't have the "lip" on the blades like the new prop. Probably been reworked over the years.......if boats could tell stories. I'm the 4th owner
 
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Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,428
That's good information.......both props sitting beside each other on the bench looked identical except the Black Max didn't have the "lip" on the blades like the new prop. Probably been reworked over the years.......if boats could tell stories. I'm the 4th owner
Maybe it has more cup as designs may change over time.
 
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