New Sportmaster Allison mods?

[K-DAWG]

So, the sportmaster that comes on the new 250/300r is a larger diameter unit. Has anyone looked at having the Allison mods done to one to see if it runs better?

Not going to lie here. Spending 17k on a new motor for my XB-2003 is a lot more attractive than spending 40-70k on a used/new XB-21.

[TB21]

I wouldn't reduce the skeg size on the 21' Allison. Just my opinion.

[K-DAWG]

I wouldn't reduce the skeg size on the 21' Allison. Just my opinion.

I thought the Allison mod was not just that but also closing up one water intake, shaping the skeg to be like a airplane wing round on one side and flat on the other and possibly blunting the nose some.

[TB21]

True and I think all the mods are good except the skeg size reduction. That's on the 21' boat.

I thought the Allison mod was not just that but also closing up one water intake, shaping the skeg to be like a airplane wing round on one side and flat on the other and possibly blunting the nose some.

[hooken203]

You are correct. But I agree with TB21 I would not reduce the size of the skeg. I question making the nose blunt also. I have had the theory behind it explained to me but you don’t see the off shore guys doing it. Our bullet nose is barely in the water when we are running anyway.

[River Rocket]

Agree. I wouldn’t cut the skeg and the Bullet isn’t in the water so I’m not sure why it needs to be rounded. I haven’t heard why that is done.

I will I’ll take it a step further and say I think cutting the skeg is dangerous and those lower units should be avoided if you are pushing the speed envelope in any of the big 3 fast bass boats.

[K-DAWG]

Agree. I wouldn’t cut the skeg and the Bullet isn’t in the water so I’m not sure why it needs to be rounded. I haven’t heard why that is done.

I will I’ll take it a step further and say I think cutting the skeg is dangerous and those lower units should be avoided if you are pushing the speed envelope in any of the big 3 fast bass boats.

Some of the biggest names in Allison Boats running Mercury's have and still do mod 2.5 lowers. Never heard of any accidents being caused by a Allison modded lower unit. In fact I think its done for safety reasons. Not sure if I agree with you on the last part of that statement. For that matter some even cut the nose off the sporty and have those coned.

[NOTGSXR]

I guess I should sell my boat...

[TB21]

On a 20' Allison the full Allison mod is great. I've run both on a 21' and I can tell you that above 90 the smaller profile skeg is not good!

Some of the biggest names in Allison Boats running Mercury's have and still do mod 2.5 lowers. Never heard of any accidents being caused by a Allison modded lower unit. In fact I think its done for safety reasons. Not sure if I agree with you on the last part of that statement. For that matter some even cut the nose off the sporty and have those coned.

[K-DAWG]

On a 20' Allison the full Allison mod is great. I've run both on a 21' and I can tell you that above 90 the smaller profile skeg is not good!

I am not talking about the smaller skeg profile. There are other things that are done to the lower besides cutting the skeg and making it fit the old fleetmaster profile. I am talking about makin one side flat and the other side rounded and closing up one water inlet. Lee should be able to speak to this he has done it and still does to lowers.

[TB21]

I thought I agreed that all the mods except reducing the skeg profile were good. Post#4.

I am not talking about the smaller skeg profile. There are other things that are done to the lower besides cutting the skeg and making it fit the old fleetmaster profile. I am talking about makin one side flat and the other side rounded and closing up one water inlet. Lee should be able to speak to this he has done it and still does to lowers.

[AllyFishing]

Here is what I've learned over the years owning an Allison, some if it experience and some of it by listening to others "in the know" and that I respect on this subject......as TB21 explained, the full Allison mod to the sporty gearcase (close up a water inlet, round the nose, cut the skeg to the profile of a stock 200 2.5liter case and then massage the sides of the skeg) was done for the 20 foot Allisons running the 2.5 Liter motors. And yes I've seen and read about JC or tooter or titus actually cutting off the nose on a sporty and adding a nose cone with different pick ups and something about changing the angle of the nose in relation to the propshaft but again that was in the days of the 2.5 liter and smaller boats. And from what I've read it made them faster.

The bigger XB21 in my opinion is a different animal. It's heavier and hanging a 505 LB 3.x liter motor and now an even heavier 4 stroke on the back is in need of a full size skeg or "rudder". My 300XS has a stock sporty and it handles better than what my 250XS with the full Allison mods did on this same boat. I "feel" like it is tracking better with less overall steering input. I admit I'm not a good WOT-up to the last tenths of a MPH driver- I guess I don't have the reflexes to make the corrections as fast as needed with the cut skeg but I can drive my 300 better at higher speeds over the 250.

K-Dawg, that's just my experience and opinion. I did, however, have much higher water pressure with the water inlets modified and will have that done again but NOT cut the skeg

[Tim Powell]

Do not cut the skeg on the big Ally, especially if you are pushing for a big number.

[K-DAWG]

Just find it odd that guys are willing to sand the pad of their boat, have props worked but, want to run a completely stock gearcase. Again for the thousandth time I am not speaking of changing the skeg profile to the size like people run on a 2.5 gearcase. There were other things done besides cutting the skeg. I was just asking a thought provoking question.

[Huckleberry]

Just cut the skeg off! ... Hell with a skeg!

[River Rocket]

Sorry, this got off track with skeg cutting. I guess we are all passionate on that subject.

Good topic.

Some on here have modded lower units. Mine has a few tweaks, basically cleanup. I can't comment on if it does or doesn't help. I just like them clean. I may be testing the covered water inlet mod soon on mine. I run a static jackplate and never move it so it will be easy to tell how it impacts day to day driving over several trips in different conditions.

As for the R gear case, the water pickups are much lower. This really helps get the motor out of the water. We saw 1/2 to 3/4" higher engine heights vs. other XB21's that are pushing max height with Opti's.

The only area I can see working on with the R case is to the very bottom back side of the bullet by the prop or shaping the skeg a little. Those are the only parts in the water with the higher running height.

This post has mentioned rounding the nose of the lower. I have no idea what that does. My nose is almost 1" out of the water at 30mph and climbs as speed builds. The nose spends very little time in the water already with an Opti sportsmaster. It will be even less on the R.

[AllyFishing]

K-Dawg, I think it is agree upon in this post that there are benefits to doing everything except cut the skeg. Inlet mods will help increase water pressure. The rounded nose may help bring the water back to the sides of the gearcase before it hits the prop. I do remember Darris saying something about that.

[NOTGSXR]

I guess I have a piece of junk...

[River Rocket]

I guess I have a piece of junk...

A face only a mother would love. Do you even have a boat? LOL.

[NOTGSXR]

A face only a mother would love. Do you even have a boat? LOL.

Good question lol