Props

[PuraVida]

I just switched back to a 15x13 on a mojo with a 400 from a 14.5x12 (acme 2079). I couldn't be happier. Lowered my surf rpms and allowed me to surf faster. I was running 10.8mph at 3900rpm now I go 11.1mph @ 3500rpm with a harder/longer port wave. Note: these are skim speeds, surf style speeds are faster for better airs.

The engine seems happiest below 3500rpm but that is just my opinion.

[PuraVida]

I should also mention, neither prop got my boat on plane with full ballast and a small crew so I opted for the lower surf rpms. Ballast = 4200lbs water, 650lbs lead

[KnoxMojo]

Not sure where you’re getting your information.

Have you measure the prop clearance on the Supra with 1.5:1 transmission? Mine has 1.5” of clearance with a 15” diameter prop.. 2020 didn’t change prop angles or even the shaft diameter. There’s no problem going to a 15.5 or 16” diameter prop. .5” of clearance is all you need.

Go ahead, let me know how that prop burn treats ya... I'll listen to the engineers at Skiers Choice that I personally know and Eric at over at OJ...0 prop guides out there recommend over 15" for the 1.5 transmission, but you can run a 16" with edge 1.76.

[larry_arizona]

Go ahead, let me know how that prop burn treats ya... I'll listen to the engineers at Skiers Choice that I personally know and Eric at over at OJ...0 prop guides out there recommend over 15" for the 1.5 transmission, but you can run a 16" with edge 1.76.

Good info, this says the shaft angle must have changed on the 1.76.


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[KnoxMojo]

Good info, this says the shaft angle must have changed on the 1.76.


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The blower motor for 2020 is still 1.5.. the rest of the 20s are 1.76.. only 19s with 1.76 are the later 450s. All 18 and below are 1.5.

[MJHSupra]

^^ Drew Tinker has been updating people on Facebook with this same info ^^

The mid-year 2019 still throws people off with the 450 and 1.76.


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[larry_arizona]

It’s possible the 2020 Supra’s with the 1.76 utilize a longer driveshaft to gain more prop clearance to the hull.

Maybe that is the limiting factor in the 2018’s to not fit a 16” prop??


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[KnoxMojo]

Longer shaft or different angle

[z28ke]

Question for you guys:

I have the OJ 945 (15x13) on my 2018 Max 400 and on really hot days when fully loaded with a big crew she struggles a bit to sustain anything over 11mph surfing. I’ll turn on the blower to help keep air circulating through the engine compartment but it’s basically running WOT at about 4000 rpm.

I’m not concerned with top speed, so long as we can cruise at 25mph. I’m considering the acme 2419 (15x12) which wakemakers has as the heavily weighted/high elevation prop. I would also like to lower surf rpm, which leads us to my question.

Going to a 15x12 will theoretically increase my rpm at any given speed (including surf speeds) but given we are dealing with water, it’s not going to be linear like differential gears in a car. Is it possible the 15x12 could lower my surf rpm due to reduced “prop slip”?

Thank you for your insight and experience!

[Stazi]

Yes. The engine will probably be “working” less with the 15x12 and you will probably see a drop in rpms to attain the same speed with less prop slip.


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