DF115 prop issue beyond me...Update...

Customer has a new zuki 115 4-stroke on a 24ft pontoon...<br />Came from a Kansas City dealer set up for sea-level operation with a 17P prop....<br />we're at close to 4000ft here. I asked him to check his WOT after the break-in period and 5200 is all it would do with just him in the boat. He is an experienced boater and knows a thing or 2 about trim, so I know he achieved max RPM.<br />I know he needs to be near 6K alone so I suggested a 13P thinking we'd gain 800-900 RPM and put him just right....well, I was WAY off...Now it gos to 6400 which is apparently the rev-limiter as it killed the ignition, or cut it in half I should say... he shut it off and restarted and it ran fine but kept it at no more than 6k...<br />Check my math here...since when has 4" in pitch resulted in a 1200 RPM gain???????<br />Needless to say, I own a 13 pitch and am buying him a 15.<br />Any insight to why this would make this big of a jump on a 'toon?????

Re: DF115 prop issue beyond me...Update...

as the engine approachs its power band at the upper RPM limits it makes more power. sometimes the math does not account for the extra few ponies at the top end. I own a few props myself <br />did ya ask him what it would turn at sealevel? most times altitudes under 6000 ft or so does not affect EFI like carbs.

Re: DF115 prop issue beyond me...Update...

The dealer says it will turn 6100 at 650ft above sea-level with the 17....I think he's full of crap.<br />Another item that is bothering me is the customer said the prop would not go all the way on, so he pulled it on with the nut....what kinda deal am I going to run into at the lake????? I hope I don't need a prop puller, cause I ain't got one that will work for that....

Re: DF115 prop issue beyond me...Update...

What do you usually put on a 115? Mine came with a 3x14x19. Just curious.

Re: DF115 prop issue beyond me...Update...

Totally dependant on the application, and what the expected WOT will be, verified by testing to get a base-line to have enough info to install the correct prop....

Re: DF115 prop issue beyond me...Update...

Have you considered gear ratio in the equation? Gear ratio is 2.59:1 on the 115. What diameter prop are you trying? I have a Johnson 140 4-stroke (2.38:1) and experienced similar. These engines need a large diameter prop (14"). I tried some of the 13.25-13.50" diameter props. With these I had to over-prop just to get out of the hole and keep the prop from ventilating but once I was planed out, I couldn't achieve top end WOT. Neither the boat or engine performed well until I got a 14". Stiletto makes a good SS prop specifically designed for the Johnson/Suzuki 4-strokes, around $300 shipped. Call Kathleen Cridlin at Stiletto 1-800-944-4576. She will take your information and make a recommendation. She dialed me in first time around.

Re: DF115 prop issue beyond me...Update...

To hit it right on the first try is almost impossible if no base-line data is available..JD, you had other props for referrence

Re: DF115 prop issue beyond me...Update...

I agree and I'll be the first to say my experience is limited but.... I don't think your customer will ever realize top performance until he goes to a 13-3/4 - 14" diameter prop. Most if not all of the 15-spline props available were designed for 2-strokes with higher gear ratios and are small diameter. Sure, they will fit the shaft but that's about it.<br />The only constant base line reference is diameter. Go to the Suzuki site. Out of the 16 props they offer, only 1 prop is less than 14" for these engines, must be a reason? http://www.suzukimarine.com/sr05/df11590/ <br />Hey man, I beat my head against the wall for almost 3 months trying to get one of the 2-stroke, small diameter props to work without any degree of success. You asked for some insight, I shared my experience.

Re: DF115 prop issue beyond me...Update...

From my Suzuki book for DF115 5000-6000 r/min.<br /><br />Prop selection chart:<br />3x14x17<br />3x14x18<br />3x14x21<br />3x14x23<br />"If the standard propeller fails to meet the above requirement, use another pitch propeller to hold the engine speed within the range specified above".

Re: DF115 prop issue beyond me...Update...

Try applying that at 4000ft elevation....<br />Suzuki also makes a 15 pitch, and several in 13-1/2" diameter.<br />JD, Thank you for the input....I meant no disrespect. Diameter has it's purpose but Diameter isn't a direct issue relating to RPM in a std application. Also, a std cup prop is very inefficient on a 'toon. The 17P that came with the boat is a Zuki prop and I was told by the dealer I knew nothing about props when I told him we would need a lower pitch at our elevation...he said he would eat leather if the 17 would not pull atleast 5800 at our elevation, so he was not happy to hear it would only pull about 5200 +/- 50 with 1 on board, with no extra weight.<br />Where I screwed up, as Rodbolt pointed out, was the fact we were way below the power band at 5200, which proves my theory of keeping the RPM at the top of the range, and experience a greater amount of power available above 5600, hence the 1200+ RPM gain with 4" decrease in pitch. I have a 13.5X15P Suzuki prop sitting right here to try on friday and see what I get.<br />This prop is listed to fit 2004 and newer DF 115, and of course it is stainless, so the diameter is less, but it has more aggresive cup which I believe (I know) is needed for a 'tooner.<br />I will let you know how far off I am with this one...

Re: DF115 prop issue beyond me...Update...

Unless they offer something other than what's on their web site, the one 13.5 X 15 is the ONLY prop less than 14" in diameter offered by Suzuki for the 90-140 hp 4-stroke engines. This was what I was referring to in my previous post.<br />I believe you have the DF's and the DT's mixed up. (DF Four Stroke, DT Two Stroke). Check the application chart again.

Re: DF115 prop issue beyond me...Update...

I sell props for a living, JD....This IS for DF 115...I made a bad choice on the 13 (I now own) and researched some issues with Peter Dean at Propco on this, even though he doesn't build a production prop for this yet, he has been testing a bunch of prototypes and this is the one he has found best suited and is building a prop as the same demensions as this one.<br />I have looked into aftermarket versions, and most are double and some tripple cupped for this application-not for the 2-strokes, the 4-strokes.<br />With all due respect, don't get hung up on diameter, it's one of the variables on the list that falls close to the bottom in prop design and affects how high you can run an engine, in high mount applications....Blade shape and cup design is the most important factor to consider.

Re: DF115 prop issue beyond me...Update...

We run from sea level to 7,000 feet no problem.

Re: DF115 prop issue beyond me...Update...

Not at the same RPM....

Re: DF115 prop issue beyond me...Update...

Kenny,<br />I know you are very knowledgable, I've read your posts and you have helped many. You gave me good advice on props quite a while back. I'm certainly not challenging your experience or knowledge. I do however know that diameter is an issue, an important issue with this particular line of 4-strokes which is all directly related to the unusually low gear ratios. <br />I will say one other thing (respectfully), you're almost as hard headed as I am.<br />I wasn't tooting Stiletto's horn, just found a company who has apparently researched the issue we've discussed. They only offer 14" props for these engines and the one I got from them works great.

Re: DF115 prop issue beyond me...Update...

Stiletto makes a hell of a prop, no doubt there.<br />I'm taking 3 new props for the zuki test-run tomorrow...I will let you know what I find, and you may verywell be right.<br />What makes you think I'm hard-headed????

Re: DF115 prop issue beyond me...Update...

since when has 4" in pitch resulted in a 1200 RPM gain???????<br /><br />Maybe that's why it's called "generalized rule of thumb" and not "absolute" ...

Re: DF115 prop issue beyond me...Update...

After testing about 250 props for different manufacturers, 350 is closer per 2".<br />600RPM average per step is very uncommon, and as Rodbolt has made clear, the 4-stroke obviously produces a higher torque curve closer to the max RPM...this is not the case with most I've dealt with.<br />

Maybe that's why it's called "generalized rule of thumb" and not "absolute" ...

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Thanks for clearing that up......I'll keep that in mind for the next 250...

Re: DF115 prop issue beyond me...Update...

walleyehed<br /> sometimes proping the 4 stokes gets funny. most the time EFI is not affected by altitude below about 600ft. most modern systems use a mass air pressure(MAP) sensor to allow the fuel and timing curves to compensate for altitude changes. however I have seen some HPDI motors that were affected some. the torque and HP curves on the big 2 strokes go up and down almost linearly. not so with a 4 stroke. the 4 strokes tend to flatten the torque curve several thousand RPM below the max power curve. its due the the design of the engine. the 2 stroke inputs a power stroke on the crank each time the piston goes to TDC. the 4 stroke its every other time. for 2 engines with the same approximate bore and stroke. stroke being the offset from crank centerline(a lever) that the connecting rod big end attaches to. if you take two engines like this and cut ones power strokes by half what happens? this is what happens with a 4 stroke. getting back to props.<br /> the advancements in 4 stroke technology is similar to the auto industry in the late 50's through the early 70"s. motors, transmissions and suspension systems made mighty leaps. by 1969 you could buy a factory 425 HP car from the show room floor and drive off. the major drawback is the tires never kept up. we could shred them.<br /> as top fuel went rapidly from about 165 to over 270MPH all of a sudden front tires were shredding. almost like the NASCAR stuff of the 60's. seems most manufacturers overlooked the fact that with a different torque curve the same prop used for years on the 2 strokes just aint gonna work on the 4 strokes.I just did a 33' grady with a pair of F225's. complaint was port engine 400 RPM below the stbd and when he hit a wave it would drop by over 1000 RPM. brand new mirage props. yep we have a local dealer that saves money by using non yam stuff. I switched them back to 151/4x15 saltwater series from 15x15 mirage and the problem went away. but there is no way they will ever convence me the same prop on the 4 stroke will react the same on a two stroke of the same basic bore and stroke. never gonna happen.<br /> so for now we at the tech level have to figgue out how to make the products perform to the sales literature. good luck with the testing and let us know how it gets resolved. dont even get me started on idiotic service reps and the strange things they try to tell us .

Re: DF115 prop issue beyond me...Update...

dont even get me started on idiotic service reps and the strange things they try to tell us

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This is where I have a question...If "This" engine is not affected by altitude (3% reduction in air density every 1000ft) and is capable of maintaining the same RPM with 12% less air available for combustion, yet is normally Asperated, and the dealer tells me it WILL swing the 17P 6K at 650ft, why am I only getting 5200 RPM at close to 4000ft????<br />Could there possibly be an engine issue??(I know...stupid question, because of course there "could" be an engine issue in any situation").<br />I' will be leaving shortly to hit the water...I have 3 I want to try on the Zuki and a couple for another guy that lives there..I have 19 props loaded for my own playing this weekend, as michigan has supplied me with 2 new prototypes, and I have a hand-full of composites to try out-see if I can peel the blades off.. <br />We'll see what happens with the Zuki..I'm going to try a few different designs on it..both SS and alum. I will report back on sunday sometime.