Oct 14

Oct 14 Allison Grand Sport with Mercury 150 Pro XS: The Incredible Sport Boat Shines

After I did the Allison Grand Sport project with a Mercury 150 four stroke I knew it would be popular. The reason is that running a 150 four stroke on an Allison was a little out of its element and somewhat controversial. I never knew how popular it would be, I get countless emails and messages about the boat to this day. Several readers repowered their Allisons with new four strokes and some bought brand new Grand Sports with 150 four strokes. One such reader and friend of Wave to Wave is Brandon Balabus of NY. He ordered a beautiful new Allison Grand Sport, white with black stripes and a new 150 Pro XS.

For the record, I loved my Allison and it was a project as well as my personal boat. The Grand Sport is one of the best sport boats of all time. There is really nothing quite like it when it comes to performance, practicality and usability. Allison thought of everything when it came to designing a family boat that is also incredibly fast. Keeping in mind, the Grand Sport was actually designed in the early nineties. For Brandon, who comes from a long line of performance boating with STVs and other boats, he really wanted something family friendly and this is where the GS shines.

A true family performance boat. Compact but loaded with storage and great design features makes the Allison Grand Sport very practical.

After seeing what was possible with our slightly modified Mercury 150 four stroke, Brandon ordered his with the Pro XS version of the 150, which wasn’t available when I ordered mine. He also opted for the Grand Sport “elite” which has a few more features, including a padded sundeck. The Pro XS has stiffer upper mounts, a 6,000 RPM limit and a different gearcase with 2.08 gears, whereas the regular 150 has a 1.92 ratio. I added the Pro XS mounts to mine and coned the gearcase.

Brandon ran his gearcase briefly before getting it coned, which is absolutely necessary on a boat like the Allison, where you need to run the gearcase very high to reduce drag and get the most out of the hull. As one would expect, the stock gears were a bit too low and Brandon was running higher pitch props just to get it to run the right RPM. The good news is that the common 4.88” gearcase had many gearsets offered over the years, so Brandon ordered some 1.85 gears that he installed this spring.

When it comes to setup it always takes a little trial and error. Before the gear change, with a 30” Promax prop, running the prop shaft ⅜ below the pad, he saw 77.7 MPH. Then ¼ below with a 32’ ET he got the RPM to 6050 and ran 80 MPH. That was with a half tank of gas.

After swapping gears, 3/16 below the pad and with a 28” ProMax it ran 78.5 MPH. Raising the engine to 1/16 above the pad and the 28” Promax, Brandon got 5900 RPM at 80.6 MPH. This is with a ¾ tank of gas. And I can speak from experience that makes a huge difference on the GS. For me to get to 80 MPH with mine, it had to be the lightest load possible, including almost no gas. Brandon probably has a couple MPH in his. He tried an ET at the higher height but didn’t like how it felt.

Brandon is running slightly faster than mine, not surprisingly, the extra 200 RPM has the Pro XS making 5 more HP but the gear ratio and higher rev limit allow the use of the slightly lower pitch prop, which can be more efficient. Mine hit the 5940 RPM limiter with the 28”, although it was a great prop all around.

From all accounts this GS is another example of an incredibly useable family rocket. 80 MPH+ in a 20’ family boat that seats 5 and has room for coolers and gear is unfathomable to most. Brandon runs it Long Island NY with some other go fast boaters. The ability to haul the family and also break 80 MPH is great, never mind doing it so efficiently. You appreciate the efficiency at the gas pump for sure. Thanks to Brandon for sharing his beautiful Allison and the great shots around Long Island.