Horse Power options for a 1976 170

[akbridge]

I'm thinking of running nitrous.

BTW, anyone know what would be a good prop for the 17, running a 115 Two Stroke?

-Fletch

A 17 inch pitch three blade should do well. Are you going to run a backplate or use it for skiing?   If so you might drop down an inch and go to a four blade.  I think merc props fit that engine.  That opens your possibilities up.  Merc props are some of the best.

[Fletch170]

The only thing I'll be pulling behind the boat is a minnow bucket.

[Fletch170]

Since I'm not doing any skiing with this boat, is a 21" pitch,  13 3/4 " prop going to work? I want to get the most out of my top end. Will this bog the motor?

BTW, I have a 97 115 Yamaha 2 Stroke.

[akbridge]

Thats too big for your engine.  Your hole shot will be slow.  And your top will be poor with you engine always lugging.   I run a 14 inch pitch and have a mean hole shot and mild topend.   A higher pitch does not mean more speed.

[kraw2]

I changed my mind again....

After going thru amd repainting the Evinrude 70 hp. my friend wanted it really bad for his work barge.

He was in a bind and needed it right away to keep working.

Because of his lack of patients (sp) with working on outboards he traded me (2) 5Ohp, (2) 90hp, and a 115hp. All the motors are 1990's and above with the 115 being a 1995. The 115 has 150 psi all around. I will sell the others for parts if they are not worth the time to get right.

[Fletch170]

How about a 17 pitch, 13.2 diameter prop? Yamaha shows that the recommended prop is 17 pitch and 13 diameter....but I can't find a 13 inch diameter prop?

[akbridge]

That prop will be fine.  The pitch is more important than diameter.   A smaller diameter will allow a quicker rev up and can help with hole shot.  The pitch determines the boat speed relative to engine speed.  I like this website: http://www.rbbi.com/folders/prop/propcalc.htm most gear cases use 2.0:1 ratio, figure a max speed of 40 mph, 10% slip and engine speed of 5250 rpm.

[Fletch170]

I really thought I would get 45 mph out of her. Oh well, I guess I will be better off having an all around good prop.

[jsakat1]

I have a 130 on my 87 170, and the fastest I gotten is 46. I think the mounting on the motor has contributed to such a slow performance. But I redid the floor and transom, with no wood and I think it will be faster. The day that I put a 4-stroke. I was looking at a 115 yamaha, but weight wise is a lot. The 90 4-stroke looks like a better fit.

[Fletch170]

I knew I wouldn't be building a speed machine, but I think the 115 yams 2 stroke is the perfect power for this boat.

[Capt Matt]

4 strokes are for barges and the retired lol
Capt matt