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MASTERCRAFT PROSTAR 5.7 BEST PROP


Dacon62
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For a ‘17 Prostar with Ilmor 5.7 At around sea level and our crew is skiing between 32-34 mph and 15-32 off. What do you feel is the prop (3 or 4 blade/prop model) that gives the best pull/holeshot while keeping the rpm in a normal range (around 3300 rpm@32 mph/3500 rpm@34 mph). Don’t want or need a prop that provides stump pulling power but revs to the moon at ski speeds. Thanks in advance.
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Eric at OJ made a custom 709 (added cup) for my '15. Added about 2 mph top end and lowered rpm's by 200 at 34/36. And from what I can tell, there's no loss in the hole shot. I had the same question, and the best advice I received was to just call OJ direct.
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43mph top end consistently, but did hit 44 while low on fuel on glass water. I was between 41 & 42 prior. I cannot remember off hand the exact rpm's, but I want to say from 3,650 to 3,450 at 34 (my slalom speed)? It's somewhere in that range, but 200 lower at 34/36 compared to my stock 709...sorry my memory escapes me.

 

I called OJ before purchasing, telling Eric I just wanted a little more top end, and if the rpm's could be lowered at all. I was actually curious if a 3 blade might be better for my needs, but he said the 4 was the better wheel for the Prostar 5.7. Our elevation is only 800' above sea FWIW.

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Master Craft spends many hours each year testing props with there team skiers. Why would you want to change the prop from the recommended size for tournament use? It you take the rpm down you will sacrifice your slalom performance The boat is low in the torque band giving you a sluggish pull in the course taking longer to come up to rpms to keep the boat in tolerate By lowering the rpm you will also sacrifice your hole shot. Reading this it seems that everyone is fixated on top end speed. These hulls are not designed for speed past 43 mph or so. Just my 2 cents.
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@dave2ball I’m just curious to lower engine rpm for fuel usage and engine life. Maybe a bit less noise too?

Without sacrifice to skiing. For a 32 Off and longer skier, not sure the power band change would be that much different.

5.7 has plenty of holeshot. I don’t know many people that “drop the hammer” on any modern boat.

Don’t care about top speed.

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@skimtb a 5.7 with the recommended prop has plenty of hole shot. When you start reducing the rpm the ski will not come through as well because you are waiting on the boat. You are not going to save that much fuel turning 200 rpms less and in my option it won’t affect engine life as long as you do the recommended service Noise is relative to the boat owner.

 

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I concur, 200 less rpm means larger throttle opening and less manifold vacuum for same speed.

Same work has to get done so x amount of fuel have to get converted to heat to do the same work .

I suspect fuel savings to be marginal.

Engine life, also negligible savings and even possibly counterproductive

Fewer power pulses for same distance traveled means each pulse has to have more energy to get same work done than at the higher rpm , thus higher peak side loads on pistons.

If these engines are babied with frequent, quality oil changes like most are, the modern roller cam engine has extensive life ahead of it

 

 

 

 

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As little difference 200 rpm would make anyway.....engine noise is not always directly proportional to rpm. As mentioned before in the amount of work needing to be done, engine noise is more related to the work being done than RPM.

 

I dont remember the rpms at 36mph, or the max rpm on that engine, but I believe I did do the math before, and we're right around 80% max rpm at 36mph. As long as we are at or below that, I don't think we need to worry about engine life.

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I didn't see in the 2018 owners manual list what the stock prop is, and I couldn't find a 2018 approved tow boat list that shows which prop was tested. Does anyone have a source for this? I'm wondering if I have the stock prop as I'm turning 4000 rpm with a skier @ 36 mph on the 5.7.

 

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The "709" series prop is the standard prop and it's been updated twice in the last few years. Original was labeled 709, then the first update was labeled 709-MF, latest update is labeled 1709 and is the approved prop for 2022. The OJ 867-MF is the 2022 approved 3-blade prop. It's primarily for jump or high altitude. Never tried one, but I would expect it to run higher RPM.

 

2022 Approved Tow Boats

 

My course at the lake house on a public lake is very shallow at one end. As a result I have at least one of each of these iterations. Each iteration is an improvement in lowering RPMs w/o any lose of hole shot. And if you're a frequent OJ customer, they start sending you t-shirts w/ you prop purchases and repairs :wink: I have a few t-shirts now.....

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