Power band question

[merc1250bayliner]

So I've been playing with jetting, props, with my modified 150 2.0. It has wh22 carbs, intake spacer, CCM reeds, stuffers, exhaust ports raised to 1.6", 28cc heads, and slight chest cut similar to a Promax cut but not as much material removed.

My final top speed number is 46.7mph at 6400rpm. I want to get to 50mph. My best preforming prop is a 16p enertia. I want to go to a 19p enertia. But my question is will I be fine to drop my RPMs with the higher pitch prop? My factory recommended rpm range is 5000-5600rpm. I'm guessing that has increased with the chest cut. If the new prop drops me 600rpm or so will I still be in the new powerband? Also I don't wanna lug the motor too much on a 2000lb boat. My pistons and plugs look perfect after checking them a few times on wot shut downs.

Trimmed down WOT rpm is 6000 and all the way trimmed up is 6400. The humid summer air will lower that some and I'm not gonna run around at max trim all the time. This is my first modified outboard so help is appreciated.

[25two.stroke]

go to a 17. Don't drop your WOT rpm back down to 5500 it won't be happy. Keep it 5800 to 6200

[rgsauger]

What’s it going on? Post pics of your setup at the back end of the boat. Are you high enough?

[merc1250bayliner]

It's a heavy deep vee 19ft bowrider

[rgsauger]

Setback and engine height?

[merc1250bayliner]

Motor is mounted to transom and cavitation plate is even with the bottom of the boat. I don't think I can go any higher. It struggles to carry the bow as is. I know this boat isn't made for speed but it's still fun trying to improve it. 50mph is my goal. I'm 3mph away from that.

[aj06bolt12r]

Sounds like you are going to need some setback. The setback will use leverage to help carry the bow so you can run more neutral trim and higher engine height.

[merc1250bayliner]

I will try that. Thank you for the help.

[OnPad]

Motor is mounted to transom and cavitation plate is even with the bottom of the boat. I don't think I can go any higher. It struggles to carry the bow as is. I know this boat isn't made for speed but it's still fun trying to improve it. 50mph is my goal. I'm 3mph away from that.

Cavitation plate should be above the bottom of the boat.
1.5 to 2 inchs will probably give you the 50mph you are looking for.

[Jim Speros]

I agree with OnPad.
Plus many boats have wedges formed into the running strakes to help them run flat and plane off easily. Put a straight edge on the strakes and corners of hull at transom.
On boats its not only about how much power you have its also about how much drag you don't have.

[cameronj]

I have a Larson 186 SEI deep vee around the same weight with a 175 2.5 on it (bobs tuner, solid mounts, drilled exhaust with a nose cone which hurts on this boat) and run 62mph GPS any day all day and when i was doing the interior with just two seats in the boat ran 66MPH. I assume like mentioned above it is setup related, when i raised my motor to the top hole i gained 3MPH and plane time improved drastically. I'm running a 23P tempest with solid PVS plugs which is able to lift the bow nicely. Best prop for lift was a new gen 24P high 5 with extra cup which lifts the stern like nothing else but not as fast as the tempest.

IMO I would raise the motor to the top hole(mine is bolted to the transom too) and get a tempest prop or another good with lift. On mine i have tried dozens of props a 19P,21P and the 23P tempests i tried all run the same RPM 5850 just different MPH. I would assume you are coming out of the powerband at 6400 and a 17p will run around the same RPMs with a bit more speed. Can you get a 21 or 23P tempest or high 5 22P to try?

One thing i would mention is steering as my single cable snapped, you should def check that as it was a hairy experience.

[merc1250bayliner]

I have hydraulic on it right now. I have a highly modified 2.5 block that I can swap once I get pistons and heads. But for this year I want to maximize the 2.0. I don't have anywhere around that will let me try props. The Enertia has been way better than anything else so far. More rpms and higher top speed. I am curious about a Tempest but I don't think I will be able to spin enough rpms. The enertia with that x7 alloy has thinner blades and seems to get me more rpms in a given pitch. But if I found a cheap enough tempest I would definitely consider trying it.

[merc1250bayliner]

I have a Larson 186 SEI deep vee around the same weight with a 175 2.5 on it (bobs tuner, solid mounts, drilled exhaust with a nose cone which hurts on this boat) and run 62mph GPS any day all day and when i was doing the interior with just two seats in the boat ran 66MPH. I assume like mentioned above it is setup related, when i raised my motor to the top hole i gained 3MPH and plane time improved drastically. I'm running a 23P tempest with solid PVS plugs which is able to lift the bow nicely. Best prop for lift was a new gen 24P high 5 with extra cup which lifts the stern like nothing else but not as fast as the tempest.

IMO I would raise the motor to the top hole(mine is bolted to the transom too) and get a tempest prop or another good with lift. On mine i have tried dozens of props a 19P,21P and the 23P tempests i tried all run the same RPM 5850 just different MPH. I would assume you are coming out of the powerband at 6400 and a 17p will run around the same RPMs with a bit more speed. Can you get a 21 or 23P tempest or high 5 22P to try?

One thing i would mention is steering as my single cable snapped, you should def check that as it was a hairy experience.

I looked up some pictures of the Larson sei. It looks like you have a flat pad at the transom. Mine is a vee at the transom. That might be where some of the difference comes from.