Pitch for a 175hp Johnson

[Snoopy1]

looking for some advice - I have a 17.5 foot bowrider with a 1993 Johnson 175 HP. I need to purchase a new prop. I have borrowed a 21 + sst prop (stainless) from a friend. The motor's redline is 5,500 rpm (I believe). With no trim the motor runs at 5,150 rpm. With a touch of trim (maybe 25%) it runs up to 5500. I am going to start with an aluminum prop and want good (not great) hole shot, good midrange, and very good top end. What pitch would you suggest? thanks for your help. Also would a four bladed prop work well?

 

[Hooty]

Re: Pitch for a 175hp Johnson

I'd play with that 21 until I found out what it will do. Trim the engine out some more and see what happens. Be sure and maintain stability but see how fast and max. at 5900.<br /><br />c/6<br /><br />Hooty

 

[Jack Shellac]

Re: Pitch for a 175hp Johnson

According to the OMC manual, the WOT range for your motor is 4750-5750 RPM. With the 21", you're at a pretty good spot now at 5500. If you switch to aluminum, chances are you'll lose some RPM with the same pitch. The saying is that you can run an additional inch of pitch with SS and get the same RPM as aluminum because the blades are thinner. If you can, get with a shop that will let you try out propellors and return if necessary. Props are tricky to predict and you never know how they will turn out on a particular rig. Oh yeah, I believe I'd stay with the 3-blade prop.

 

[Snoopy1]

Re: Pitch for a 175hp Johnson

Thanks, but know I am confused - The dealer where I bought the motor from said the redline is 5500 rpm? Was he just being overly cautious or can I safely run upto 5,900 rpm? If I can then I should expeirment more - because the motor seemed to have alot more left but I was very careful not to go over 5500 - with a touch of the trim it got to 5,500 in a heart beat and the boat was rock solid.

 

[Dhadley]

Re: Pitch for a 175hp Johnson

Depending on which ignition you have the rev limiter is either at 6200 or 6700. <br /><br />5900 to 6000 with an average load should be a good target rpm.<br /><br />Good luck!