Allison Grand Sport, Merc 150 gearcase modification.

[Wave to Wave]

I finally got around to working on our Mercury 150 gearcase. We have an aftermarket nose cone on the stock 150 case. It was too pointy, and had a some issues with the skeg. I basically blueprinted it by rounding out the tip, refinished the leading edge. And, I redid the skeg, smoothed it out, and made the edge better. It made the boat faster, and now we are on the rev limiter at 77 MPH, stock ProMax 28", at 5950 RPM. We should be in the 81-82 range now with a 30"

Wouldn't it be great if Merc made the 150 ProXS version with a sportmaster 1.75? Or if Mercury Racing got a hold of it, to make a 150 R and 200 R version of this lighter platform.

Here's the article.

https://www.wavetowave.com/home/2019...cation-testing

[url=https://flic.kr/p/Rvo6rZ]

[Wave to Wave]

There is a link in that article to our gearcase article, where we get into some details of gearcase dynamics.

https://www.wavetowave.com/home/2019...our-lower-unit

[xb03fs]

How high is the motor height now? How much setback and how much lip. Now that you have a lwp, start working on motor height. At the right height driving becomes so much easier. Too low sucks as much as too high... for sure get a 30 promax as well. 85 may not be out of question.

[Wave to Wave]

How high is the motor height now? How much setback and how much lip. Now that you have a lwp, start working on motor height. At the right height driving becomes so much easier. Too low sucks as much as too high... for sure get a 30 promax as well. 85 may not be out of question.

Mathematically, it probably won't run 85, but 81-82 is in the cards. Engine is maxed out on the plate right now, at about 1/4 below the pad. Will probably raise it one hole when I get the chance. It's 7.5" setback.

[xb03fs]

May want to consider 10” I believe that is what most grandspirts used to run, xb2003 runat 14”. This will get prop back in cleaner water and lower slip.. don’t count 85 out just yet.

[Props4u2]

I use to set them up with 12" plates with 225 PM engines.

[Strokerdean]

Hello Lee, glad to see your still around.

[xb03fs]

If lee says 12 go straight to 12

[NOTGSXR]

If lee says 12 go straight to 12

Pretty much lol

[mittenbass]

Great article on lower unit design, btw

[Bamaman]

Hard to believe how efficient Allison's hulls are. And after all these years in production, that boat still has stunning good looks.

If you held off to 40 mph, I wonder how efficient on fuel that 4 stroke would be?

[Wave to Wave]

Hard to believe how efficient Allison's hulls are. And after all these years in production, that boat still has stunning good looks.

If you held off to 40 mph, I wonder how efficient on fuel that 4 stroke would be?

10 MPG. If we lowered the engine and played around with it, maybe 11 MPG.

[Wave to Wave]

I use to set them up with 12" plates with 225 PM engines.

Ya, those engines are a little lighter, so that makes sense. But so far this setback seems good. Will try it higher and see how it goes.

[AllyFishing]

That is a great article. Especially the explanation on rounding the point and filling in the starboard side inset under the sporty.

[Props4u2]

Ya, those engines are a little lighter, so that makes sense. But so far this setback seems good. Will try it higher and see how it goes.

Even though it's a little heavier, try it you'll like it.

At least go back to 10", the extra set back will be the easiest MPH and economy you will get now that you have the low water pick up coned unit.

A 28p 3-blade over hub ET prop will also be the best all around and fastest prop.

[Chad2002xrd]

What is the rev limit on a pro xs 150?

[Wave to Wave]

Even though it's a little heavier, try it you'll like it.

At least go back to 10", the extra set back will be the easiest MPH and economy you will get now that you have the low water pick up coned unit.

A 28p 3-blade over hub ET prop will also be the best all around and fastest prop.

Thanks Lee. Will look into that soon. May mes with it this summer. Will raise the engine one hole too.

[Wave to Wave]

What is the rev limit on a pro xs 150?

The ProXS revs 200 more, to 6,000. But probably goes to 6,200 before guardian. If the ProXS had a higher gear ratio, like a 1.75, it would be amazing.

[Jackson Gore Ar.]

Could you put 175 in it? Is it possible? If so, that boat will run great. Honestly it's amazing to think that a 2.5 260 will run a grandsport in the 100's. Then the new 150's will run 80- maybe close to 90 with 175 gears... just amazing.

The ProXS revs 200 more, to 6,000. But probably goes to 6,200 before guardian. If the ProXS had a higher gear ratio, like a 1.75, it would be amazing.

[Wave to Wave]

Got a chance to run a Billy Eaves 26" Trophy, for cruising. And a 30" ProMax, but didn't get a chance to raise the engine, it's maxed out on the jack plate right now. Just haven't had a chance.

With ProMax 30" it could pull 77 at 5600 RPM, so if I can just raise it 1/4 could probably get over the hump and get 81 to 82 theoretically. The Trophy is a great daily driver prop, accelerates better, handles amazing. Love the Trophy for cruising.

30 ProMax fuel mileage:
35 MPH at 2700 RPM = 11.7 MPG
50 MPH at 3500 RPM = 8.7 MPG
58 MPH at 4100 RPM = 8 MPG

26 Trophy Fuel:
50 at 3800 RPM = 8 MPG
59 at 4800 RPM = 6.9 MPG
65 at 5200 RPM = 6.4