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2 Stroke WOT, Newbie Question

Old 03-19-2019, 02:01 PM
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Default 2 Stroke WOT, Newbie Question

So I bought my first boat roughly 2 months ago. The boat is supposed to run between 4500 and 5500 WOT and trimmed up it rides at 5k. Everyone has told me that 2 strokes want to be run so I have been running full, although I go short distances, between islands 1-10 minute rides. There is also a lot of pulling back for passing bigger boats and breaks of no wake zones. As you would imagine, I have been burning a ton of gas and oil so I of course decided to start searching and it seems I am being dumb. Where should I be running my boat? 80% is 4k which would put me around 25mph on a 115. Should I be lower? Should I prop up to get to 5500 so I am not losing out on that range? Does it matter? I mean if I drop back from WOT and go to 4500, would that not be the same as riding WOT with a bigger prop and being at 4500 for a little less throttle?
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Old 03-19-2019, 02:08 PM
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Most motors be they 2 or 4 stroke find the most economical range between 3,000 and 4,500 rpms. Running WOT full time is expensive as that is the point of maximum fuel consumption. Prop and trim inpact fuel consumption and ride. But it seems different for all boats. That is because not all 30' exact boats made by the same mfgr weight as much or less than the indicated catalog weight. Some can be 1,000# Overweight. Only way to know is public scales.

I run my boats at point of least vibration. On my 4 strokes it seems to fall between 4500 and 5500 Rpms correspondint to 35 to 45 mph. My most economical speed is at 3500 RPMs or 26MPH but it runs smoothest at 4,100 to 4,500 RPMs. I had a 2 stroke that loved to run at 4200 rpms. (I sold it at 5792 hrs on tiny tach.) Not most economical but smmoooooth.

Last edited by solarfry; 03-19-2019 at 02:18 PM.
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Old 03-19-2019, 02:10 PM
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If your engine is reaching the recommended rpm range, then you are alright. Now you can run it any way you see fit. There is no need to only run it at wot all the time. If you care to cruise at 3500rpm you can certainly do so. This will save gas and also wear and tear on your engine. Two strokes seem to be happier if they are able to run at or near the top end of their RPM band. You should be good to go. And enjoy your toy!
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Old 03-19-2019, 02:12 PM
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First off you prop down to raise rpm, you could go down 2 deg in pitch but is it worth it probably not.
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Old 03-19-2019, 02:23 PM
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I've had a couple of larger two strokes (Merc and Evinrude V6s) with aftermarket fuel management, Lowrance EP-60R sensors. On each boat fuel efficiency was best right as the engine came "into the pipe" so to speak. Both boats would plane easily around 3800-4000 rpm, but around 43-4500 the engines would sort of take off for lack of a better term. If you have two stroke dirt bike/jet ski/snowmobile experience you will know exactly what I'm talking about. Run it right there and that's where the best fuel economy was by a significant margin. Fuel economy around the 3800-4000 range was 10-15% lower, and WOT was even worse.
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Old 03-19-2019, 02:46 PM
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Originally Posted by brownman View Post
First off you prop down to raise rpm, you could go down 2 deg in pitch but is it worth it probably not.
What is a degree of pitch?
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Old 03-19-2019, 03:37 PM
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A theoretical number of inches the prop will travel in one revolution, takeing into account zero slip.
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Old 03-19-2019, 03:45 PM
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Originally Posted by BlueRudy View Post
What is a degree of pitch?
Well, there are 360 degrees in a circle. Now how many inches are in the circle?

What about that 3rd degree? What is up with that?
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Old 03-19-2019, 03:45 PM
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Originally Posted by brownman View Post
A theoretical number of inches the prop will travel in one revolution, takeing into account zero slip.
Where do the degrees come in? How many inches to a degree?
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Old 03-19-2019, 04:39 PM
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Your friends told you to run it wide open, they forgot to tell you "occasionally" during the day. Your most efficient cruise will be just after the bow of your boat comes down (planes). Most typically run around 4000 rpms like you stated.

Regarding your prop, is 5000 WOT when your boat is not loaded down? IE 1/4 tank gas just you? Or 5000 full tank normal operating load? If 5000 rpms is running light I'd change props 2 pitches lower so that your boat isn't bogged down when running heavier.
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Old 03-19-2019, 07:24 PM
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Not to be disagreeable, but prop pitch is usually expressed in inches. The pitch describes how far forward the prop would advance if it made one complete revolution if it were threaded in an imaginary tube. Thus if the prop had a 15” pitch, it would advance forward 15”. There are other factors such as slip, etc. This is the same pitch we talk about with machine screws (nuts and bolts). Prop diameter is expressed as inches also.
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Old 03-20-2019, 04:18 AM
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It's fine. Don't start messing with things that aren't broken or you'll end up tearing the whole boat apart and end up hating the boat.

Run it at 4000-4200 for max fuel economy. If you want it to get on plane sooner, have a higher top end and save gas add a hydrofoil to the cavitation/ventilation plate.
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Old 03-20-2019, 04:45 AM
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Originally Posted by Gulfripper View Post
. Everyone has told me that 2 strokes want to be run so

2 strokes dont "like" to idle for long periods of time... they tend to load up and foul plugs... what "they" meant by that was dont idle around all day.. give it some gas and get on plane once in a while, not run wide open.
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Old 03-20-2019, 06:03 AM
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Every boat has a "sweet spot" when the hull gets up on plane and will stay there.Depends on the boat and motor combo,but assuming you are propped correctly it's probably going to be a few hundred rpms over when it planes.That will likely be your most economical cruising speed.Your motor should be powerful enough to give decent speed without running around at full throttle all the time.
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Old 03-20-2019, 06:52 AM
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My 2005 90hp Johnson 2 stroke, which I've owned since 2007, likes to run at about 3,200 to 3,500 RPMs for maximum efficiency. I rarely run it WOT unless I am troubleshooting something, or there is a lightening storm coming in.
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Old 03-20-2019, 07:42 AM
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Engines aren't human. They have no likes, no dislikes, and they don't get tired nor do they need to rest.

For older, non-DI 2 strokes, a 50:1 gas to oil ratio was a good compromise. Any less than that and you had insufficient lubrication at high RPM's, and any more than 50:1 would foul plugs too easily at idle speeds. The "fix" was after a day of trolling, go ahead and run that thing at WOT for a few minutes to clear everything out. Some people were scared of running an engine at full throttle, and the phrase "they like to run" came about.

Assuming you have sufficient lubrication and cooling, running at wide open throttle does little harm. That said, by knocking down the throttle just a little, you only lose a little speed, but still cut down significantly on your fuel burn rate. For instance, I burn about 20 gph (gallons per hour) when running wide open. If I pull back on the throttle just a little, I can get it down to about 14 gph. That means I cut my fuel consumption rate by just about a third, but it didn't cut my speed by 1/3 - more like a couple of mph. So that means I'm much more efficient at 3/4 throttle than full throttle.

As others mentioned, you can learn where the sweet spot is - that's where it has its most economical planing speed. And like SweetD above, I run WOT for an occasional baseline/ troubleshooting, or if I'm trying to get the hell out of dodge.
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Old 03-20-2019, 07:59 AM
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Originally Posted by Scupperz View Post
It's fine. Don't start messing with things that aren't broken or you'll end up tearing the whole boat apart and end up hating the boat.

Run it at 4000-4200 for max fuel economy. If you want it to get on plane sooner, have a higher top end and save gas add a hydrofoil to the cavitation/ventilation plate.
If hydrofoils were so magical, don't you think manufacturers would be building them in as an advertising point? How do you square "Don't start messing with things that aren't broken or you'll end up tearing the whole boat apart and end up hating the boat" with drilling holes into your anti-ventilation plate and thereby weakening the structural integrity of it to add a hydrofoil?

I would personally never put a hydrofoil on a boat. If the prop is wrong fix that. If it doesn't already have proper trim tabs, this is a great investment on any boat.
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Old 03-20-2019, 08:12 AM
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Originally Posted by VTXrider View Post
If hydrofoils were so magical, don't you think manufacturers would be building them in as an advertising point? How do you square "Don't start messing with things that aren't broken or you'll end up tearing the whole boat apart and end up hating the boat" with drilling holes into your anti-ventilation plate and thereby weakening the structural integrity of it to add a hydrofoil?

I would personally never put a hydrofoil on a boat. If the prop is wrong fix that. If it doesn't already have proper trim tabs, this is a great investment on any boat.
You obviously fail to understand anti-ventilation plates. Hydrofoils if you will.

Why are trim tabs (an accessory) so good (great investment in your words) whereas a hydrofoil (an accessory) is so bad? What engine maker recommends trim tabs as some solution to some particular problem?

Why are some propellers a solution to a problem but hydrofoils cannot possibly be so?

Anti-ventilation plates don't have to be drilled to mount a hydrofoil. You must not have gotten the word. They have only been around about 20 years or so.

Are the folks that have installed a hydrofoil and seen performance improvements so wrong in their assessment?
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Old 03-20-2019, 08:38 AM
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You don't say what kind/size of boat or whether an older or newer 2-stroke (carb vs FI, DFI, ?)...only that it's a 115hp doing 25mph at 4k rpm, so I'm assuming something like a v-hull 18' CC or DC?

Every boat like that I've ever had with a 2-stroke (whether older carbed or now a DFI Opti), properly propped, got best fuel economy at somewhere between 3500 and 4000 rpm.

(And also got best hole shot with a vented s.s. 4-blade prop and a set of trim tabs...)
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Old 03-20-2019, 09:23 AM
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OP, here are some thoughts for you to ponder to try to draw some of the previous comments together:
  • If your engine is not revving to its max revs then you are "driving in a high gear". Most people like to get their outboards set up so they can make max revs when properly trimmed at WOT
  • Two major things affect max revs: prop pitch pitch and engine height
  • Engine height is a big one: if it's too low then the lower unit is buried and this has various effects: low RPM, slow to plane, high bow attitude.
  • Hydrofoils also seek to fix these same problems (slow to plane, high bow attitude) but you should get the engine height right before adding a hydroplane or you are just adding a band-aid and not addressing the root cause. If you just can't get the engine high enough to solve planing and attitude issues then a hydrofoil is the way to go (which is why you see them on so many stern-drives where you can't raise the engine height).
  • Once you have the engine height right you can then play with the prop to get the max revs where you want them. Once again, you can change props without messing with the engine, but lowering pitch to compensate for poor rigging isn't going to get you your best performance.
  • Once you have the engine running at max revs at WOT you can experiment to find your most economical cruise. This is very dependent on the hull/engine combo so experimentation is the key. Fuel flow sensors aren't terribly expensive and are easy to install - if you really want to find your cruising sweet-spot then that's the way to go.

Alternatively, you can ignore all that and drive somewhere near to 4000 RPM as others have said, which is usually pretty efficient for a 2-stroke. Give your engine a WOT blast once an outing and it will thank you, otherwise a solid 2-stroke will run all day long at around 4K
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