I have read that most allisons tend to run better with the prop above the pad. Is that relative to the size of the jackplate?
Example:
9" plate, prop to pad 1/2" below
12" plate, prop to pad even
15" plate, prop to pad 1/2" above
I have read that most allisons tend to run better with the prop above the pad. Is that relative to the size of the jackplate?
Example:
9" plate, prop to pad 1/2" below
12" plate, prop to pad even
15" plate, prop to pad 1/2" above
Last edited by big_o_tom; 11-17-2017 at 06:54 PM.
That's right. The more set back you can run, the more motor height it likes. also depends on the gear case and the type of prop.
Where on the gear case does it tell the ratio?
It is usually stamped on the flange that bolts up to the mid section. At least that's how Sport Masters are. You would need to remove the lower to see the impression stamp.
AND the deciding factor on engine height is which boat /hull you are talking about and whether or not the lip is stock
2013 Allison XB-21 BasSport Pro
2023 Mercury Racing 300R
Bravo FS 30P
ProMax 30P
from my experience a stock lip Allison I have never had to go above the pad to reach big top end numbers.
Especially true on the XB2002's and XB03'sOriginally Posted by myron
2013 Allison XB-21 BasSport Pro
2023 Mercury Racing 300R
Bravo FS 30P
ProMax 30P
.... Raise your mota up.
I have no idea. I have talked to people with 2003's who claim to run over a 1/2" above the pad and others who say the sweet spot is around a 1/4" under. I try to stay even and below and I have never had a bad experience with mine. A lot of those that said you cant run above the pad are the same ones who told me to that I had to run a 5.5" set back to run a 3.0 liter motor. They were wrong, that killed the performance of the boat. I am at 13 inches back now and think 14 would be even better. Just be careful with whatever you chose to do.
I've owned 4 xb2003s. 3 of them had stock pencil roll & ran great 1/8-1/4" below.
The other had most of the roll removed & it ran as high as 1 3/4" above.
2024 Xpress X21 / Yamaha 250 SHO
2022 Allison XB-21 BasSport Pro Elite / 2022 Mercury 300R (Sold)
Depending on horse power, 1 3/4" above the pad is VERY HIGH even with "most" of the roll removed. Wonder what the actual measurement of the lip was on that one?
I did not do the work, a previous owner did, but I think the pencil roll was almost completely removed.
I went back and check my old written records just to be sure & I ran several props at 1 3/4" above.
I ran a 200xs and a 225X on that boat.
2024 Xpress X21 / Yamaha 250 SHO
2022 Allison XB-21 BasSport Pro Elite / 2022 Mercury 300R (Sold)
How much setback?
IMO, the only time you really need to go over 1/4 above, is one for drag racing which I would run 1.5" above and second for all out top end run. The main reasons you raise the motor is less drag and more rpms.
Xb2003 - 300xs
100+ mph club
Well I definitely don't want to go to high. I have a 9" allison plate and a 225 pro max with a 25° trophy plus. When the prop was at about 1" below pad I couldn't drive it fast with a lot of trim, to much chine and I couldn't control it. Now with the prop at pad level it seems to want to blow out with some trim. Still need to drive it more and used to it.
2003 like 13-15” setback with the heavier the load closer to 15” and the lighter the load closer to 13”
The higher you go the, less trim is needed. In a perfect sense, you want the engine at absolute level, a prop with the least amount of cup to carry said weight and as high as you can go without blowing out over light to moderate chop. No sense in flirting with a triple digit blowout, they're plenty fast set up conservative and if its not enough, score you a 475lb XR hull and have fun with a little 2.5.
I've read everywhere that my boat needs 14"-15" set back, but I have also read that allison changed the hull some around '97/98, and those hulls need a little more.
I ran my boat today at 1/8th below pad and it didn't want to blow out at all. I have a 9" plate with a 25° trophy plus and 76 was my max anything more and wouldn't be safe. And this is at just about neutral trim. Anything more and it's to squirrely.
I guess my question here is do I need a bigger plate to drive my boat faster?
simple answer is no, if your steering is good setup good a good gearcase it will run fine, it sounds like you just need to be patient and learn to drive the boat. Try to find someone close to you that can spend some time with you learning, once you get it, it will become second nature to you.
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