prop size for flightcraft 18xl with 2 speed trans

Postby roypedo » Mon Dec 04, 2017 12:32 pm

Hi all,

I've got 86 Flightcraft 18xl 350chev with a 2 speed ezyski transmission-for those that don't know, it has a normal 1:1 gear and a low gear. and can be shifted whenever(its actually a converted 2 speed power glide so fluid coupled)
i currently run a 12x15 prop, pretty standard for a 350 chev, but i top out at about 3300rpm and only hitting about 60KpH, and it sometimes battles to pull skiers out when the boat is fully loaded.

As the low gear is super low, it is basically useless-revs out in about 1 second and get almost no boat speed up.
Generally i just use the 1:1 gear as it has the power to pull up most slalom skiers fine, but again when its fully loaded it sometimes struggles.

So my theory/question is, if i change the pitch to something much higher i could use the low gear to pull people out of the water and then cruise in the top gear once their up depending on size and weight etc, I'm sure for smaller people on wakeboard the top gear could pull them out anyway.
and it would give me much higher speed for when not towing.

Does this makes sense? does anyone have any experience with this type of transmission/boat/setup? can anyone offer some advice on prop size etc etc????

Thanks,

Roy
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Re: prop size for flightcraft 18xl with 2 speed trans

Postby 82Juddcraft » Mon Dec 04, 2017 10:27 pm

I'd be interested too see the outcome.
Whats the LOW range gear ratio?
Or speed at 3300rpm in LOW might give us a rough idea.


If its just a 2 speed powerglide automatic yeah why not!

Just for a reference my gear box is permanently 1:2.2 with a 28 pitch prop.
And 3000rpm feels like a good skiing speed.
Only thing I'd look more into is stress on the gear box in HIGH range.

Its like a ute towing with 35in mud tires some gearboxes weren't made for it.

But those Powerglides have a good reputation in Tractorpulls and down the strip.
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Re: prop size for flightcraft 18xl with 2 speed trans

Postby mof » Tue Dec 05, 2017 12:49 pm

If you're only getting 3300 rpm wide open throttle then a taller prop could be worse. I've got no other help to offer, but 3300rpm seems pretty low revs for flat out
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Re: prop size for flightcraft 18xl with 2 speed trans

Postby roypedo » Tue Dec 05, 2017 1:55 pm

wouldn't a higher pitch prop have higher speed at lower rpm?

and not sure on ratio, seems really really low geared, but i know theres heaps of different ratios that can be ran in powergildes...
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Re: prop size for flightcraft 18xl with 2 speed trans

Postby 82Juddcraft » Tue Dec 05, 2017 9:46 pm

I thought 60kmh was the quickest roy wanted to go and he was sacrificing top end speed to achieve more down low.
5000 is where u should top out.

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Re: prop size for flightcraft 18xl with 2 speed trans

Postby feral1 » Wed Dec 06, 2017 8:14 am

Your current prop might be a bit out of whack if that is all the rev's you are getting, or maybe your engine needs a tune or something, you should be able to pull 4200 + with that prop on 1:1.

For what it's worth, I have a 20' skicraft excel with a 270hp mercruiser, velvet drive with a 1:1 ratio. That came with a 12 x 15 prop and I would get about 4400 revs, holeshot was a bit disappointing compared to my old boat. I had it repitched to 12 x 14 and had some small performance gains and gained a few extra revs. I then switched it to a 12.5 x 12.5 acme 4 blade prop. Down low and holeshot was an awesome difference and I didn't loose any top end really, still pull 4500 revs at about 75km. I can't comment on your low gearing though
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