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Suzuki DF350 - high or low mounting

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Suzuki DF350 - high or low mounting

Old 03-30-2019, 01:04 AM
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Thumbs up Yam F350 -> Suz DF350 switch completed - first direct comparison

Finally got the boat put to sea, and been through enough of the break in period to put it to the test, so here is the first direct comparison:

Top Speed

Yamaha F350
51 knots 5600 rpm

(an average WOT value, record is 52,5 knots, it's dependent on water surface and temperature)
1,45 ltr per nm at 30 knots

Suzuki DF350
46,5 knots 5500 rpm

1,35 ltr per nm at 30 knots

I clearly need a different set of props, and that is fine: the combination of my boat and the DF350 has never been tested anywhere, so the deal I got from the start was that they will change props with no cost for me until I get the best set. But the 5 knot speed difference it a bit worrying. Say what you will a about the F350, but it is strong as hell.

I will hold off on a complete comparison across the entire rev range until I get a more fitting setup, but other first impressions are these:

Engine Noise
Suzuki is noisier, and sounds like a bus compared to the Yamaha V8 at lower revs. It sounds good once you pass 4000 rpm though
Handling
No planing threshold. Like, at all. This surprised me. I am not just talking fast acceleration, but I can leave it at any RPM and the boat stays perfectly level.
Economy
The litre per nautical mile ratio is significantly better that with the Yamaha. But, I am also running a set of props that are way to big / high pitched, so will hold on until I get the correct set.

Summation
Not that impressed for now, will hopefully gain a couple of knots top speed at least with props that allows the engine to reach the max HP range of 5700-6300 rpm.

Last edited by amerelium; 03-30-2019 at 01:13 AM. Reason: subject text
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Old 03-30-2019, 03:39 AM
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Maybe you need to raise the Suzuki up on the transom.
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Old 03-30-2019, 03:48 AM
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Assuming you had the right prop on the Yamaha F350, I would think you would want to wait to post this comparison until you felt that you have the right duo props on the Suzuki DF350? Having the wrong props on one engine does not lend a lot of credence to an engine comparison.
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Old 03-30-2019, 04:58 AM
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...which is what I said I am doing - point was; unless a better set of props gets med another 4 knots, it is a weaker engine than the yamaha
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Old 03-30-2019, 05:11 AM
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My boat with Yamaha 350s is faster at WOT.

My boat with Suzuki 350s is more fuel efficient across the board.

Pros and cons to each brand. Once you get the props dialed in I will estimate your top speed to be a few knots slower but more fuel efficient

You need to prop it carrying a decent heavy load and get as close to 6300 as you can

One bit of advise, these df350 motors on my hull want max trim. At cruise of 42mph I'm usually 40% trim up. WOT I am 90 to 100% trim up
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Old 03-30-2019, 07:15 AM
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Originally Posted by First Light View Post
Assuming you had the right prop on the Yamaha F350, I would think you would want to wait to post this comparison until you felt that you have the right duo props on the Suzuki DF350? Having the wrong props on one engine does not lend a lot of credence to an engine comparison.
That is a valid assumption but you know what they say about the word "assume" I assume.

Without knowing if the F350 propeller was the optimum one or not it is about impossible to try and compare the performance of the two motors. OP might be able to prop the DF350A so that it has better performance than the F350 but without knowing if the F350 was optimally propped or not, we really can't get there from here.
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Old 03-30-2019, 07:22 AM
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Originally Posted by Whaler27 View Post
Maybe you need to raise the Suzuki up on the transom.
The F350 might have performed better if it also had been mounted higher on the transom. if the two motors are not mounted at the exact same mounting height (propeller shaft relative to the bottom of the boat hull actually) then all bets are off when trying to compare performance.
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Old 03-30-2019, 08:08 AM
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Judge has had the opposite with twin engine application on the back of their 36 Chesapeake. The DF350 was a few kn faster and much more fuel efficient. That was in flat confined waters. Who knows if the V8 or Duoprop would have the advantage in a sea.


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Old 03-30-2019, 08:57 AM
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Fwiw... found on EPA database
Yamaha makes the full 350hp and peak torque is 334ftlbs @ 4200
Suzuki is rated at 344hp and peak torque is 319ftlbs @ 4500.
Of course comparing these numbers on paper is one thing but the differences in lower unit gearing and duoprop vs single prop probably resulted in the numbers OP is reporting. Keep us posted once broken in and dialed in if your numbers improve at all
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Old 03-31-2019, 02:57 PM
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OP, thanks for the information. Do you know what your boat weighs (loaded), and what the deadrise at the stern is?
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Old 04-02-2019, 12:41 AM
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...well, dealer wants to raise the engine height before trying new propellers; I'm not sure I quite a optimistic as him about how much will be gained from that, but I guess I'll find out may 2nd (1st service booked)

Weight with some fuel should be around 2400 kg, deadrise I think is 40 cm

By the way, I managed to break the tilt lock levers. The design is ridiculous; when you engage them and retract the tilt cylinders, the engine is lowered like 20 cm into the water again, leaving the inner prop submerged. I tried putting a block under each of them to limit the movement, but one of them slid out, and the jerk made the lever snap off. And of course with all the load on just one side, the other one snapped off as well, cleanly at the base.

Fortunately, it's not expensive to replace...
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Old 04-02-2019, 07:33 AM
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I have some experience with DF350s using jackplates. You can raise them quite a bit without the props blowing out, but the best speed and economy is lower.
If you posted it, I missed the pitch you're using currently. Seems like with the speed you're getting at that rpm WOT, you should be in the 22.5-24 range.
Curious as to why you would use trim lock levers to keep the motor trimmed out of the water (I'm assuming while moored).

Last edited by jeff.p; 04-02-2019 at 07:54 AM.
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Old 04-02-2019, 11:21 AM
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Originally Posted by jeff.p View Post
I have some experience with DF350s using jackplates. You can raise them quite a bit without the props blowing out, but the best speed and economy is lower.
If you posted it, I missed the pitch you're using currently. Seems like with the speed you're getting at that rpm WOT, you should be in the 22.5-24 range.
Curious as to why you would use trim lock levers to keep the motor trimmed out of the water (I'm assuming while moored).
It's to retract the pistons into the cylinders when the boat is mored - if you just raise the engine up and leave them out, shit will grow on them, and might get into the cylinders when you lower then engine, and ruin the whole tilt unit. Happened to my first outboard.
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Old 05-04-2019, 07:12 AM
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...so, the engine cannot be raised on the transom any further, because of the placement of the lower bolts - apparently the setup isn't as identical to the Yamaha as they claimed; looking at the upper bolts it can be raised two levels. Ride height is ok though methinks; the anti-cavitation plate is skimming just above the water when running at speed.

Which means new propellers. So, do I go for decreased diameter or pitch? I would think if the idea is to reduce drag, then reduced diameter is the way to go? I want what is optimal for top speed - 4 knots (4,6 mp/h) slower WOT speed with the same amount of horsepower is underwhelming to say the least.

Any thoughts?
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Old 05-04-2019, 02:11 PM
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Default Suzuki DF350 - high or low mounting

...hmm, posted this earlier, but it vanished. Making a new attempt:

So, I seem to have started quite the discussion on FB; Some claim that the dual props prefers clean water to run in - undisturbed by the hull, and that engine should be mounted relatively low. Others that it prefer to run more shallow than single propped engines (which is what I have been told before also).

Any thoughts?
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Old 05-04-2019, 02:19 PM
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You want the anti ventilation plate at or above the water. I would say higher the better as mine do not cavitate nearly like my prior single prop engines but are mounted same, water washes over occasionally.
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Old 05-04-2019, 02:34 PM
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They do not like to be high. I tried mine at every level. They got better the lower they went. They were horrible when too high.
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Old 05-04-2019, 03:12 PM
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Originally Posted by MakoMyDay View Post
They do not like to be high. I tried mine at every level. They got better the lower they went. They were horrible when too high.
So you got better performance when it was lower?
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Old 05-04-2019, 03:24 PM
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Originally Posted by amerelium View Post
So you got better performance when it was lower?
yes. Both at cruise as well as top end. I’m sure there’s a limit to it, but I ended up on the lowest hole.
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Old 05-04-2019, 04:01 PM
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Originally Posted by MakoMyDay View Post


yes. Both at cruise as well as top end. I’m sure there’s a limit to it, but I ended up on the lowest hole.
...hmm, interesting.
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