Top speed prop help

[Josh_Bovaird]

Hey guys I've got a question on my boat I'm running an 04 Triton 176 magnum with a Suzuki 115 4 stroke with a 3 blade 21p stainless prop.  My big thing is I'm hitting rev limiter and having to back off if I keep pushing it.  Would a different prop give me more speed and not be so close to redline?  Kinda new to this whole outboard and prop situation.  Thanks again!

[jbh3]

" Would a different prop give me more speed and not be so close to redline?"

Yes to both. Try a 23P.

[Way2slow]

My first question is what makes you think you are hitting the rev limiter.  For that size boat with a 115 on it, a 21" pitch prop sounds about right. 

I think that motor has a redline of 5,750 rpm, and the rev limiter is usually a few hundred rpm above that.  So unless you are turning 6,000 rpm or more, I have serious doubts about it's hitting the rev limiter. 

If you are not turning over 5,800 rpm, I would suspect an engine performance problem, spark plugs, plug wires, fuel system, or something along those lines, but I dang sure wouldn't be wasting my money on a prop, because if you go to a bigger prop and it's not against the limiter, you are only going to make it run much worse.

Now, if you are turning 6,000+ rpm, then definitely get another prop.

[tomustang]

What model prop?

What's your redline?

What's your top speed right now?

[Josh_Bovaird]

58 minutes ago, Way2slow said:

My first question is what makes you think you are hitting the rev limiter.  For that size boat with a 115 on it, a 21" pitch prop sounds about right. 

I think that motor has a redline of 5,750 rpm, and the rev limiter is usually a few hundred rpm above that.  So unless you are turning 6,000 rpm or more, I have serious doubts about it's hitting the rev limiter. 

If you are not turning over 5,800 rpm, I would suspect an engine performance problem, spark plugs, plug wires, fuel system, or something along those lines, but I dang sure wouldn't be wasting my money on a prop, because if you go to a bigger prop and it's not against the limiter, you are only going to make it run much worse.

Now, if you are turning 6,000+ rpm, then definitely get another prop.

Im thinking the 6000+ rpms and over rev light blinking and alarming points me in rev limiter direction.  I'm thinking another prop for sure.

34 minutes ago, tomustang said:

What model prop?

What's your redline?

What's your top speed right now?

Ill have to look and see what model prop I have and I'm hitting around 46mph without over revving.  Not sure on the exact rpm but I'm in the 6ks.

I just checked my spare prop and thats a suzuki stainless 14x22.  So I must not have a 21 pitch then i guess.

[Way2slow]

OK, you need to make sure what prop you are running right now, because if that motor has a 2.59 gear ratio and running a 21" prop, even with just 8% slip you would have to be turning 6,500 rpm.

Doing a quick prop calc show you would probably want a 24" prop.  That gives you 5,800 rpm, with 10% slip and running 46 mph.

I'm not used to those low gear ratio's, I'm used to the 1.8 stuff.

[Josh_Bovaird]

I'm pretty sure both the props are the same things

[Further North]

Specs for the DF115: http://www.suzukimarine.com/Product%20Lines/Outboard%20Motors/Products/DF115/2012/DF115A.aspx

Way2Slow's got it regarding the gear ratio - 'Zukes are a little weird that way.

My DF140 has a 6200 RPM redline with the same gear ratio and loves a 22p prop.  Depending on how many people on board or what I'm doing I have also used a 21P and a 20p.  I'm running an '05 Crestliner CMV 1850 with the Johnson version of the DF140, and with the bigger boat see about that same top speed...that 20p will have my motor running right at redline.

Edit: I forgot...Suzuki's seem to like larger diameter props...that's part of why they go with the gear ratio.

[Josh_Bovaird]

1 hour ago, Further North said:

Specs for the DF115: http://www.suzukimarine.com/Product%20Lines/Outboard%20Motors/Products/DF115/2012/DF115A.aspx

Way2Slow's got it regarding the gear ratio - 'Zukes are a little weird that way.

My DF140 has a 6200 RPM redline with the same gear ratio and loves a 22p prop.  Depending on how many people on board or what I'm doing I have also used a 21P and a 20p.  I'm running an '05 Crestliner CMV 1850 with the Johnson version of the DF140, and with the bigger boat see about that same top speed...that 20p will have my motor running right at redline.

Edit: I forgot...Suzuki's seem to like larger diameter props...that's part of why they go with the gear ratio.

Im gonna have to see if I can sell or trade my spare prop off and go with a higher pitch

[Josh_Bovaird]

Do you guys think a 14x23 prop would be better?

[Way2slow]

Probably not much.  With all things equal, and if running a 22" now, it would only drop you approximately 150 rpm.  It would definitely have to be a try before you buy deal.  With the understanding you are going to buy "A" prop, a lot of dealers will let you try a new prop before you buy it, as long as you don't ding or scratch it in any way.  Larger dealers usually have a pretty good supply of good used props also. 

Also, is that an aluminum, I seriously doubt you want to go to an aluminum if it is.  Most three blade SS props are in even numbers, and four blade SS and aluminum are in odd numbers.

[Further North]

1 hour ago, Way2slow said:

Also, is that an aluminum, I seriously doubt you want to go to an aluminum if it is.  Most three blade SS props are in even numbers, and four blade SS and aluminum are in odd numbers.

I agree 100% on going SS if possible.

Oddly, I've found that props for my Suzuki seem to come in every pitch...which is why I tried the 20, 21 and 22. 

[Josh_Bovaird]

Im sticking with SS and thinking about buying an aluminum for the rocky lakes.  Im gonna look into some bigger dealers and see, but i think before I do anything I'm gonna mess with my motor height when I can get on the water and see if that helps any before dropping the money on a prop

[WIGuide]

It'd probably be a better idea to get your RPM's down first before messing with motor height. Sure you can get your rpm's to drop by lowering it, but your introducing more drag into the equation and that will usually hurt your speed. It's possible you might get slightly more speed with the current prop if you do, but a bigger prop at current engine height would be the faster of the two and also wouldn't cause unnecessary engine strain. 

[Way2slow]

Actually, one cause of excessive rpm is the motor too high and cavitating, also over trimming.  If you've played with engine height, I would suggest you drop the motor down to about 3" below the pad and see what your rpm does. That could very easily fix the problem if you are up higher than that.  Not all props and hulls can handle the motor being raised a bunch.  

Look at your prop and see if it looks like someone has sanded a spot in the blades about the size of a quarter or fifty cent piece.