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Yam F350 - Suz DF350: 2nd direct comparison

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Yam F350 - Suz DF350: 2nd direct comparison

Old 05-20-2019, 12:00 PM
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Default Yam F350 - Suz DF350: 2nd direct comparison

...all right, so I replaced the 25 pitched propeller with 24 - it raised the max revs from 5500 to 5700, but changed nothing else, except hurting fuel economy. WOT speed remains the same.

WOT
F350 _ 51+ knots _ 5600 rpm _ 125 ltr / nm
DF350 _ 47 knots _ 5700 rpm _ 120 ltr / nm _ (25 pitch prop: 47 kn / 5500 rpm / 110 ltr/nm)

30 knots
F350 _ 3500-3600 rpm _ 1,40-1,45 ltr / nm
DF350 _ 3800-3900 rpm _ 1,35-1,40 ltr / nm _ (25 pitch prop: 3700 rpm / 1,30-1,35 ltr/nm)

Impressions: The Suzuki makes the boat reverse like a car, and it can make it handle like a water scooter. I can plane the boat at lower speeds because of the added bite of the dual prop. But it is slooow. The Yamaha engine noise is a LOT more pleasant, and the added cylinder displacement and torque simply makes it stronger (I know some don't like that word used, but it fits).

I am no quite done testing. I am going lower the engine a notch on the transom, and see if I can raise the hull a bit more out of the water by help of tilt angle before the propellers begin playing helicopter (which they do at a lower angle than what the Yamaha did). If that does not work out, I will try a jackplate and and raise the engine a notch compared to now. I know the dual propellers create more drag, but I am finding the top end speed deficit quite drastic, for the same amount of horsepower.

I am interested in comments...
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Old 05-20-2019, 12:15 PM
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You don't seem to be showing as much improvement in fuel burn as I would have expected either, so it does seem like something in your setup is leaving room for improvement. I wouldn't be surprised by you losing a knot or two, but 4 seems like a lot.
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Old 05-20-2019, 12:39 PM
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Originally Posted by Texas 17 View Post
You don't seem to be showing as much improvement in fuel burn as I would have expected either, so it does seem like something in your setup is leaving room for improvement. I wouldn't be surprised by you losing a knot or two, but 4 seems like a lot.
I think just the opposite on top end - IMO the 4 mph difference is negligible. Fuel burn is also negligible. In this instance I would go with whichever dealer/mechanic local to me I was more comfortable with.
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Old 05-20-2019, 01:21 PM
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I bet you need to lower the engine a hole.
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Old 05-20-2019, 01:54 PM
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Originally Posted by First Light View Post
I think just the opposite on top end - IMO the 4 mph difference is negligible. Fuel burn is also negligible. In this instance I would go with whichever dealer/mechanic local to me I was more comfortable with.
He's already swapped the motor, he's trying to get it dialed in. The dealer/mechanic issue is moot.

He's losing almost 10% speed on a rig with supposed equal hp... this is a meaningful loss of performance on the top end that is carried through the cruise range. And yes, the fuel difference is negligible, which was my point... it should not be. The f350 is not known to be efficient. As I stated, if he is dialed in correctly, he ought to be seeing more improvement than that. The combination of lower than expected efficiency gains and higher than expected loss in top speed equals decent evidence his set up is not optimized as it is.
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Old 05-20-2019, 01:59 PM
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I would try raising not lowering the motor, especially if its losing top end. I have heard that with the added prop surface they like to be high.
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Old 05-20-2019, 02:57 PM
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Originally Posted by Tino160 View Post
I would try raising not lowering the motor, especially if its losing top end. I have heard that with the added prop surface they like to be high.
Yeah - but because of the rigging not being completely similar - It is already mounted on the top notch for the lower bolts, even though there are two more levels to go on the upper ones - I can only lower it as it is. So going to try that first, and if the effect is negative, try raising it above current level with a jack plate.
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Old 05-20-2019, 04:20 PM
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I do not have any insite to add. Your repower is of interest to me as I'm running a single F350 on a DC 265. Thanks for posting your test results.
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Old 05-20-2019, 04:32 PM
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Originally Posted by Tino160 View Post
I would try raising not lowering the motor, especially if its losing top end. I have heard that with the added prop surface they like to be high.
I thought the same thing, but my Suzuki 350 gets the best speed and mpg with the jackplate in the lowest position or 1/2” up. It holds traction 4” up from the bottom, but for what ever reason it likes to be in the water. I’ve never had a dual prop boat and the only boat I’ve had this happen on. My boat is a twin step hull and maybe that has something to do with it as well?
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Old 05-20-2019, 05:26 PM
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I think the DF350 has growing pains. I'd hold off a little before purchasing. I bought mine August 2018 and at 140 hours currently. Water is in both my lower units. No fishing line! I have a feeling bad design. Also one of my lower units recently started making a horrible clicking sound.
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Old 05-20-2019, 05:29 PM
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Only 60 hours on mine so far, but no issues. Hope it stays that way.
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Old 05-20-2019, 05:55 PM
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Mine got faster and faster the lower I mounted them.
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Old 05-20-2019, 06:12 PM
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Originally Posted by MakoMyDay View Post
Mine got faster and faster the lower I mounted them.
Most motors I have owned got faster on the way up. Why do you think the opposite is true for the DF350? I wish one of the large dealers in south FL would chime in with their experience. I'm curious because the dealer mounted mine on the highest possible hole and at WOT I can run 100% trim with no cavitation.
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Old 05-20-2019, 06:41 PM
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Originally Posted by Empire View Post
Most motors I have owned got faster on the way up. Why do you think the opposite is true for the DF350? I wish one of the large dealers in south FL would chime in with their experience. I'm curious because the dealer mounted mine on the highest possible hole and at WOT I can run 100% trim with no cavitation.
I think they create a ton of stern lift at high rpms and dropping them lower creates more bow lift to counter act it. Just my theory though.
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Old 05-20-2019, 07:08 PM
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Originally Posted by Empire View Post
Most motors I have owned got faster on the way up. Why do you think the opposite is true for the DF350? I wish one of the large dealers in south FL would chime in with their experience. I'm curious because the dealer mounted mine on the highest possible hole and at WOT I can run 100% trim with no cavitation.
i have no idea. I just know I tried it in every hole. They absolutely hated being all the way up. The stern lift created is real. The boat ran several inches higher in the stern.

Keep in mind I also switched from f350s to Suzuki 350s.
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Old 05-20-2019, 07:18 PM
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Originally Posted by MakoMyDay View Post


i have no idea. I just know I tried it in every hole. They absolutely hated being all the way up. The stern lift created is real. The boat ran several inches higher in the stern.

Keep in mind I also switched from f350s to Suzuki 350s.
Can you explain what your motors did all the way up other than speed loss that was a negative?
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Old 05-20-2019, 08:12 PM
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Originally Posted by Empire View Post
Can you explain what your motors did all the way up other than speed loss that was a negative?

My Suzuki 350 will loose mph and fuel economy when I have the jack plate raised high. Crazy thing is the props are not blowing out, but as soon as I drive the engine down it gains speed and economy. I’m curious to hear what makomyday has experienced.
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Old 05-21-2019, 03:03 AM
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Thanks again for posting your results OP. I am considering a single Zuke for a 25 footer sometime down the road and real world results like these are very interesting.

It is too bad they don't have a bunch of different props for you to try, as it seems you would want to be propped to get about 6000 RPM WOT with the Suzuki.

From what others have experienced, it does seem that lowering might help some too.
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Old 05-21-2019, 04:59 AM
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I run mine with the cavitation plate right on top of the water surface at a neutral trim. It seams to run best there. If I run it higher I lose speed and economy. If i run it lower the boat handles like a pig and I lose speed and economy. I have been told and I have seen that the dura props do not blow out when run at high mounting, they just slip more.
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Old 05-21-2019, 05:51 AM
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Originally Posted by Empire View Post
Can you explain what your motors did all the way up other than speed loss that was a negative?

Loss pf speed at all rpms once on plane as well as loss of top end. For instance at the highest mounting it would do 32 @ 4500 rpm getting 1mpg. On the lowest it would do 38-39 @ 4500 getting 1.1. It wasn't a slight difference. I have a feeling if I could've gone lower it would've been even better. Like the others said-when raised up high, or even trimmed high while mounted low, it would not blow out-just slip a lot
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