I/O Prop Pitch

I am using a 3.0L MerCruiser Alpha I (135 HP) and need more torque out of the hole. Any suggestions regarding prop pitch would be greatly appreciated. Thanks.

Seventeen, or fifteen if you can find one. Anything that gets your revs up to a higher hp range at planing speed.

Prop pitch is the number of inches the prop would travel "screwing" through the water without any slippage. The lower the pitch number the more engine rpms it takes to travel a certain speed. Typically, you want to have a balance between hole shot, under towing conditions, and cruising. Most of the time, people with the 3.0 will pitch down 2" to improve hole shot with making the motor scream during towing and cruising. I have heard of people going as much as 4" in pitch after some experimentation. You can also use a ventilated prop (exhaust ports out the side) and also reduce diameter. Reducing diameter reduces the amount of traction each swing of the prop has and reduces the amount of engine torque to turn the prop. Even 1/2" of diameter reduction will make a large difference.

I've recommended this before on an I/O pitch issue and I still do: get a ProPulse. It's a composite prop but it has an adjustable pitch that doesn't require you to change out blades to repitch. With a 3.0L you're going to have a hard time getting decent hole shot but you still don't want to drop down too far. With the ProPulse you can tinker with the pitch each time you go out. (They say you can change the pitch in the water but you I need to have the boat on the trailer to do that.) Find the pitch you like, get a real aluminum or steel prop of that pitch and keep the ProPulse around as a spare. It's a lot easier than going through two or three props to find the right pitch and they only cost about $150. And no, I am not affiliated with them in any way, just a satisfied customer (who wouldn't have even bought the thing if I weren't in a pinch to get a prop with the ProPulse on a monster sale at WestMarine).

Also consider the option of going to 4-blade. My engine/outdrive is set up for a 23-pitch 3-blade and I've tried both a 21-pitch 3-blade and a 20-pitch 4-blade...which are essentially equivalent to one another. I liked the 4-blade...it felt a lot smoother!

Note that those pitches are for my ratio setup and will probably not work for you. I had to hold back on the throttle with the new props to keep RPM's from getting too high at WOT. Lost about 8 miles an hour on top-end speed...which was fine with me since I was topping out at 60 mph with the 23 pitch.

I recommend the Mercury HighFive Prop. The size is fully depended on your RPM's. No other prop will even touch it. 5 blades for holeshot.

I beg to differ on the highfive and no other prop being able to touch it. He is talking about an outdrive and for that if getting across the H2O is not an issue I too would recommend the hi-5 if you can test it out first. I use a shifting propeller that starts out at 17 pitch ofr a hole shot that just dosent compare. I will set the rpm range tomorrow but at aprox 3500 rpm it will shift to 21 pitch for top speed. boya big daddy now thats versitility. they are fairly spendy but for an outdrive I HIGHLY recomend looking into it.
JJ