Johnson 70HP Props

[delaney]

I have a 2001 Johnson 70 2s. Need to know which way to go on props. I have a 17' CC used for fishing. Currently running a 13 1/4x17 aluminum, cupped. Max RPM is 5500, speed 36mph. Engine in 3rd hole from top. If I go up in pitch to a 19", my rpms would probably drop but mid-range performance should improve. Is this harmfull? Most interested in cruising performance (speed/gph) but don't want to harm engine by being under propped. Don't pull skiers/tubes. Advice?

 

[ob]

Re: Johnson 70HP Props

19" pitch sounds like a bit too steep for your setup.Your current WOT rpm's of 5500 is where you want to be.Actually that engine can handle 6000.You could try raising the engine one hole at a time and water testing to insure that excessive prop ventilation will not occur at around 2/3 throttle ,on plane,while executing a tight turn.If you find that your setup is a good candidate for raising the engine a bit higher ,it will allow your engine to gain some more rpms by reducing the engines drag and backpressure on the exhaust.Overpropping your engine in the hopes of getting better top end performance will lower its wot rpms and impose excessive load(lugging) on your engine.

 

[backdraft]

Re: Johnson 70HP Props

mvsand, going to a 19 inch will not be a good idea. You have a cupped prop now which in effect gives you close to a 19 inch at the higher rpm's. The cupping works by holding the water on the blade slightly longer at high revs. Your present prop is the best of both worlds. nevjb

 

[delaney]

Re: Johnson 70HP Props

Thanks, guys. You confirmed what I thought. I'll leave well enough alone. Since I'm already 3 holes up, don't want to risk exposing the water intake. Given my set up, should I expect much improvement with a comparable SS prop?

 

[AUGIDAWG]

Re: Johnson 70HP Props

Yes

 

[backdraft]

Re: Johnson 70HP Props

mvsand, yes for the slight gain in speed and [Thats a nice prop you got there] and no because of the cost. nevjb