MAX RPM for 1999 150 oceanpro

[oyster gro]

I bought a pair of these engines (one counter rotating) but am only using one. The speed and throttle response is better than I would have hoped for but flat out it only turns 4200. Is I over propped because there was 2 engines together ? What should this engine turn ? My 15 yo son says I should just put the second engine on and be done with it. ha ha

 

[eavega]

I don't know specifically for that engine, but generally the Johnson outboards max WOT RPM should be between 5000 and 6000 RPM. You are probably overpropped for your application. Did your boat originally come with two engines? If not, what is the 150 replacing? What is the max HP rating for your boat? You have to treat your setup as brand new. What pitch prop are you running right now to get 4200 RPM? That is your starting point. You will change approximately 200 RPM for every inch of pitch ( decreasing pitch will increase RPM). Whatever you are running now, you would need to step down approximately 5" of pitch to get the motor turning in the 5000-6000 RPM range.

Rgds
Eric

 

[Chris1956]

My '98 Johnny 150HPV6 Service Manual gives full throttle operating range as 4500 -5500 RPM. I would expect it to be the same for your motor. BTW - I have the same observation. Lots of power out of the hole, but low top end, IMHO.

 

[oyster gro]

I don't know specifically for that engine, but generally the Johnson outboards max WOT RPM should be between 5000 and 6000 RPM. You are probably overpropped for your application. Did your boat originally come with two engines? If not, what is the 150 replacing? What is the max HP rating for your boat? You have to treat your setup as brand new. What pitch prop are you running right now to get 4200 RPM? That is your starting point. You will change approximately 200 RPM for every inch of pitch ( decreasing pitch will increase RPM). Whatever you are running now, you would need to step down approximately 5" of pitch to get the motor turning in the 5000-6000 RPM range.

Rgds
Eric

it is a new boat this spring and I got it custom built to my specs. so I don't know how much power it can handle, I do know the way it's built it could take a lot more engine but it has plenty now. there aren't many 26' x 9' work boats that will go 35 knots. I looked at the prop and it's 14 1/4 x 21

 

[oyster gro]

I don't know specifically for that engine, but generally the Johnson outboards max WOT RPM should be between 5000 and 6000 RPM. You are probably overpropped for your application. Did your boat originally come with two engines? If not, what is the 150 replacing? What is the max HP rating for your boat? You have to treat your setup as brand new. What pitch prop are you running right now to get 4200 RPM? That is your starting point. You will change approximately 200 RPM for every inch of pitch ( decreasing pitch will increase RPM). Whatever you are running now, you would need to step down approximately 5" of pitch to get the motor turning in the 5000-6000 RPM range.

Rgds
Eric

it is a new boat this spring and I got it custom built to my specs. so I don't know how much power it can handle, I do know the way it's built it could take a lot more engine but it has plenty now. there aren't many 26' x 9' work boats that will go 35 knots. I looked at the prop and it's 14 1/4 x 21

 

[oyster gro]

I was talking to a prop guy at the dealers and he suggested a 15 1/2 x 15. does this sound reasonable ? if it makes any difference the boat is flat bottom.

 

[Chris1956]

a 19P prop would add about 400 RPM to your WOT RPMs. That gives you about 4600RPM. A 17P prop would give you about 5000RPM. Maybe a bit more, since you may get a little more power at that RPM.

 

[eavega]

If it were me, I'd try the 17P first. Depending on the actual prop (props of the same pitch will vary in blade design and configuration, cupping, etc) that should get you in the 5000+ RPM range. The 15P would be the "safe bet" that is going to get you definitely get you into your correct range, but you might blow past that 5500 RPM when correctly trimmed out. As Chris mentioned, your motor may get a bit more efficient as the RPMs get higher, especially if you get on plane faster and now can figure in the effect of changing the trim angle on the engine. Once you get on plane, trimming the motor out will increase RPM without applying more throttle.

Rgds

Eric

 

[oyster gro]

thanks for the replies, I may try the 17p . At least with an aul prop its not a big investment if its wrong.

 

[oyster gro]

thanks for the replies, I may try the 17p . At least with an aul prop its not a big investment if its wrong.