Our stock 150 has a few hurdles to get around. One thing I didn’t realize until after our initial test was, it doesn’t have a water pressure sensor. This seems crazy, but it is plumbed in, without the sensor. We hooked up a Merc Monitor for testing, assuming we would watch our pressure to get the engine as high as possible, but we had no water pressure readout. Apparently you have to get a kit to hook that up. And, the regular 150 motor mounts are awful. You can move the engine around on the trailer with one hand. This only gets worse over time as the rubber compresses and breaks down.

Motor Mounts

As a side rant, engine builders today are so concerned about noise, vibration, and harshness (NVH), that they try to ensure you can’t hear or feel the engine. But, what happens is you try to solve a very tiny problem, vibration at idle, and you cause a much greater problem, the engine bouncing around dangerously under speed. Funny enough, there is a myth that solid mounts cause vibration; they are actually smoother at speed, and make steering way more precise. You can have the best steering system, but soft mounts render it ineffective. A classic case of trying to solve a problem that doesn’t really exist, and causing a much greater problem. When an outboard is bouncing around on the transom, it causes undue stress, you can feel it through the boat, and it negatively affects handling. I’m not saying all engines should have solid mounts, but semi solid and products like Delrin, offer a nice improvement with no drawbacks. Plus, solid mounts last way longer.

Parts List

So, our parts list is simple. We need solid mounts. I am debating whether to install the stiffer mounts from the ProXS, or get solid ones made. I am leaning toward making solid ones out of Delrin, at least for the lowers.

Next is the lower unit, we need a gearcase that has low water pickup, and can be run quite high. So, our options are limited, although we may be able to retrofit a Sportmaster somehow, I think it might be a pain to do, we will probably modify the existing gearcase. This engine has 1.92 gears, which is a slight advantage over the Pro, so with low water and a cone, we will be in good shape I think. Typically it is not an advantage until you are above 80 MPH, but we will be right there, and we need low water anyway, so it will suit our case. If you aren’t going over 80, and you don’t need to run you gearcase very high, it’s not necessary.

Once the the mounts and gearcase are taken care of, we can get a better baseline. Then, we will look at programming our ECU. This is something that will push us to that next level. Reprogramming the ECU allows the engine to circumvent the rev limiter, and supposedly can make more power. Some say, 20 to 25 more HP, and pushing the RPM to 6,700 RPM, that seems optimistic to me. I think we want to be in the 6200 to 6400 RPM range on our setup, and if HP is bumped even 10 or 15 HP, I’d be happy.

Testing

Our preliminary testing was very brief. We only had a short amount of time, but we learned a ton, and we were impressed so far. We used a Promax 28” prop, that had some modifications; the blades were trimmed at the base of the hub, this theoretically prevents exhaust gas from creeping onto the blades. So, the good news. The Grand Sport planes effortlessly with the Mercury 150, no bow rise and can hold being on plane at a ridiculous 12-13 MPH. The Allison skid planer helps, but our fears of the weight of the engine were not realized, there were no issues at all. No porpoise at all, no bad handling manners either. You really can barely hear it running at low speed, it can just cruise effortlessly all day. At about 2800 RPM, we could go 40 MPH, and get 10 MPG. That is incredible, because this prop probably isn’t the best for efficiency the way we had it setup. We can improve that number, which is already ridiculous. Because we couldn’t get a water pressure reading, we couldn’t push raising the engine, so we ran it about an 1-¼ inches below the pad, briefly tried slightly higher, and watched the temp gauge, but didn’t want to push it. With that, we ran a best of 72 MPH, at 5,400 RPM. Obviously, we want to get the RPM up, and I think we can by just slightly raising the engine.