jeffz0rz321
New Member
bone stock ski, loking for more bottom end and mid range. bent my stock prop and figured id up grade a bit. what will a 15/20 do for me and what do those numbers mean ?
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what will a 15/20 prop do for my 96 xp 800?
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Progressive pitch....
This question hasn't been asked in a long time. Our impeller are more like pumps, not propellers. We compress water into a nozzle to create forward momentum. To do this, we need a impeller that creates the same amount of force from the entire dimension of the blade.
Let me see if I can say this easy. If you look at your impeller you'll notice on the outer edges, it's not degreed as much as the inner edges. Thus, the measurement 15/20. The outer edge is 15 degree and the inner part of the blade, against the hub is 20 degree.
Now, the reason is physics. If the center of the hub is spinning (hypothetically speaking) 100 rpm, then 4 or 5 inches out on the outer edge, the rpm is much higher, say 150 rpm.
With the progressive pitch, this means, the water being pushed at the outer edge is equivalent to the water pushed on the inner edge.
I guess what I'm trying to say is it's all equal force, across the diameter of the impeller. Does that help?............
As for changing them? Your ski is set up for efficiency. Good bottom end for getting you out of the hole. Nice mid-range and good top end. If you change this, you might get quicker bottom end, out of the hole but you'll lose top end speed. If you go the other way, you'll lose bottom end torque but gain a couple extra miles per hour..............If you want to mod, look at pump wedges or extensions. You can also look at power nozzles. :cheers:
This question hasn't been asked in a long time. Our impeller are more like pumps, not propellers. We compress water into a nozzle to create forward momentum. To do this, we need a impeller that creates the same amount of force from the entire dimension of the blade.
Let me see if I can say this easy. If you look at your impeller you'll notice on the outer edges, it's not degreed as much as the inner edges. Thus, the measurement 15/20. The outer edge is 15 degree and the inner part of the blade, against the hub is 20 degree.
Now, the reason is physics. If the center of the hub is spinning (hypothetically speaking) 100 rpm, then 4 or 5 inches out on the outer edge, the rpm is much higher, say 150 rpm.
With the progressive pitch, this means, the water being pushed at the outer edge is equivalent to the water pushed on the inner edge.
I guess what I'm trying to say is it's all equal force, across the diameter of the impeller. Does that help?............
As for changing them? Your ski is set up for efficiency. Good bottom end for getting you out of the hole. Nice mid-range and good top end. If you change this, you might get quicker bottom end, out of the hole but you'll lose top end speed. If you go the other way, you'll lose bottom end torque but gain a couple extra miles per hour..............If you want to mod, look at pump wedges or extensions. You can also look at power nozzles. :cheers:
Not sure if you are a car guy, but swapping impellers is just like swapping gears in your rear differnential.
If you go with a higher gear, you take off faster (out of the hole) but then you end up with going 60 mph at 3500 rpms, rather than 2000 rpms. So top speed is lower, but you have more UPMH! when taking off.
I have a 96XP and the stock impeller is MORE than efficient for hopping out of the hole, if the wear ring is in good shape. Mine actually hops OUT of the hole when I gun it. It will hop 6-8 inches out of the water 2 or 3 times before it grabs and takes off, and maxes out around 55 mph. In about 3 or 4 seconds. That is fine for me.
If anything, a higher speed impeller might be better for the XP. It has plenty of spin and grab wtih the stock pitch. Not sure what that pitch is...
A higher speed top end impeller that may lose some bottom end grab would likely be fine for the XP, if you want faster top end speed, since the stock tends to grab too much, for my taste.
But I use my XP primarily for jumping waves, so that grab in the low end is what I need for fast take-offs and to make sharp turns and to get back into the next wave. For my Challenger, I opted for a better grab in the lower rpms and a lower top-end speed for pulling skiers and a faster hole-shot.
If you go with a higher gear, you take off faster (out of the hole) but then you end up with going 60 mph at 3500 rpms, rather than 2000 rpms. So top speed is lower, but you have more UPMH! when taking off.
I have a 96XP and the stock impeller is MORE than efficient for hopping out of the hole, if the wear ring is in good shape. Mine actually hops OUT of the hole when I gun it. It will hop 6-8 inches out of the water 2 or 3 times before it grabs and takes off, and maxes out around 55 mph. In about 3 or 4 seconds. That is fine for me.
If anything, a higher speed impeller might be better for the XP. It has plenty of spin and grab wtih the stock pitch. Not sure what that pitch is...
A higher speed top end impeller that may lose some bottom end grab would likely be fine for the XP, if you want faster top end speed, since the stock tends to grab too much, for my taste. But I use my XP primarily for jumping waves, so that grab in the low end is what I need for fast take-offs and to make sharp turns and to get back into the next wave. For my Challenger, I opted for a better grab in the lower rpms and a lower top-end speed for pulling skiers and a faster hole-shot.
jeffz0rz321
New Member
i'm gonna need a prop either way, i bent my stock prop a bit when i tok in a good size rock. wear ring is fine, but this rock got wedged between tow of the fins, and not the wear ring. getting a little vibration, and i can see that the prop is slightly bent. should i go with a stock replacement, or get something a bit more aggressive ?guessi could get a better intake grate, might help the performance. still running the stock plastic grate.
We need to know the brand and model of the 15/20 impeller. You cannot compare the same pitch with different impeller brands and models.
You need a 17/22 Swirl impeller. They are made by Skat-Trak. That 15/20 is pitched too low for your XP.
The numbers actually refer to the leading edge and trailing edge of a progressive pitch impeller. The leading edge is 15 and the trailing edge is 20 as measured at the outside edge of the blade. The pitch at the hub remains constant from the leading edge to the trailing edge.
Chester
jeffz0rz321
New Member
thats actually the prop i was considering. the 17/22 will give me a little more botton emd and a bit more mid range if im correct?
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