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jamey1e

Engine Rpm Question

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Guys the manual for my current outboard (Yamaha F70 4 stroke) says full throttle operating range is 5300-6300 RPM.  Where in this RPM range should I be operating?  Do most of you guys run at WOT?  For what it's worth the boat is a 2015 Triton 17TX and is my first.  I've never seen anything with such a wide range of max RPM which kind of left me scratching my head as to where I should be running.  Any help will be greatly appreciated.

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What kind of rpms are you turning at wot?  I rarely do wot as my engine burns a gallon of fuel every 2 minutes that way.

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I would think WOT should be at 6300rpm. The motor should have a rev limiter to prevent you from over revving the engine. As far as what speed/rpm to run, What ever feels comfortable. There should be some performance data online about your specific motor that will tell you the best performance and fuel economy

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I have a 175 Tracker w/60 Merc 4-stroke. I usually run around 4200 RPM, that's about 22 MPH. In my opinion the best way to find your efficient cruising speed, for both boat and motor, is get up to about 3,500 RPM, then quickly increase the throttle a slight amount and then run for about one minute. Keep repeating this increase procedure until you detect the RPM increase, or the sound increase, but the boat speed doesn't increase. Now drop the RPM back about 600 to 800 RPM, or what sounds good to you, and you have nailed your best cruising speed, which will probably not be your best gas mileage. Your best gas mileage will come at a much lesser RPM. You can do this procedure in a car, a boat, motorcycle, or an airplane. You are going by the combination of your instruments and the seat of your pants :)

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Thanks for the help so far guys.  I dug through the manual a little and it says that max output is at 5800 RPM so I guess that would be the point where the power will fall off and speed will no longer increase. 

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What kind of rpms are you turning at wot?  I rarely do wot as my engine burns a gallon of fuel every 2 minutes that way.

WOW a gallon every 2 minutes.  What type of engine is it?

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Several years ago, the rule of thumb was that an outboard would burn one gallon per hour for every ten horsepower at wide open throttle. 

 

A 300 hp would burn 30 gallons per hour at wot, or two minutes per gallon.

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Does anyone on here run at WOT? Engines, parts, and labor are expensive. Do not abuse your motor and it won't abuse you. There is also the boating safety factor.

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You WOT range is the range you want your engine to be able to turn when running wide open. It ensures your engine won't be lugging excessively throughout it's RPM range causing excessive wear and causing the engine to work harder than it has to. Usually you want to prop your motor so it's running near the top end of your WOT RPM range when your boat is at a normal load. 

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Does anyone on here run at WOT? Engines, parts, and labor are expensive. Do not abuse your motor and it won't abuse you. There is also the boating safety factor.

I do! While I do not have a high horsepower bassboat, I would have no qualms about running one WOT if I did. Outboards are built tough and I don't consider using full throttle "abuse" of an engine. Just my opinion, and I agree with what you said about boating safely. There are certainly conditions when it would not be smart to run a fast boat wide open.

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Does anyone on here run at WOT? Engines, parts, and labor are expensive. Do not abuse your motor and it won't abuse you. There is also the boating safety factor.

I do, anytime the conditions allow it. Granted, my boat only tops out at 43. The longest run I ever have made at WOT was 12 miles. And the only reason I went 12 miles was cause I was back at the ramp. I could have ran the tank dry that evening, the lake was so flat.

I did run over 70 miles one day during a tourney, most of which were WOT, but none of the runs were very long.

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Once you are past your break in period, you can run WOT without issue as long as the RPM is below the maximum safe zone stated in the manual. 

 

I run at WOT when I need to, often times I open her up to WOT and trim it out, then back down a tad on the throttle to save some fuel. Be courteous to other boaters when not running WOT though, you will throw out a bigger wake when not on pad at WOT. With my boat I can leave it trimmed out for WOT and back down, then when I get near another boat I hit it up to WOT again without having to mess with the trim. That allows me to send him/her the smallest wake possible, then when I get past them I back it back down again. 

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WOW a gallon every 2 minutes.  What type of engine is it?

It is a Merc Optimax 225.

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You WOT range is the range you want your engine to be able to turn when running wide open. It ensures your engine won't be lugging excessively throughout it's RPM range causing excessive wear and causing the engine to work harder than it has to. Usually you want to prop your motor so it's running near the top end of your WOT RPM range when your boat is at a normal load. 

 

+1 on this.

 

Tight lines,

Bob

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Mines about that, 22 gallons per hour, I can two hours on 45 gallons

You should always prop a motor so it will turn near the max recommended RPM at WOT with your normal load. This gives the best all around performance and economy. Now, that does not mean you have to run it that fast or at that RPM. This is just to minimize the load on the engine and is actually better for the engine.

A lot of people seem to think if they put a higher pitch prop on, they will get more speed, but usually find it slows them down. They go below the motors peak hp band so it's straining more and not making full hp.

As for running at full throttle, I usually always run my smaller motors WOT most of the time. Anything that runs less less than 50 mph pretty much stays full throttle. Until gas prices got ridiculous and I retired, I pretty much ran my faster boats at WOT. Due to the simple fact it does not take long to cover huge amounts of water in a short time at 75+ mph, I don't need to run that long at WOT, but I have gone 40 miles in a 1/2 hour several times.

 

Engines have power bands they work best in, load one down and it will not have the performance or economy it would have if it was allowed to turn up more.  My 98 4WD Chevy pickup is a prime example. I spent over $1,200 on parts rebuilding and modified the crap out of the automatic transmission in it so I could tow heavy loads in overdrive.  Well, the first time I hauled my 20' Javelin to Texas, I found out it was a waste of money.  Towing it at 70 mph in overdrive, it was getting 11.7 miles per gallon.  Coming back I decided to try it in 3rd and not overdrive, my gas mileage increase to 12.8 miles per gallon.  So even though I can tow it in overdrive, that extra load on the engine drops the gas mileage down to where it's not worth doing it. 

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Interesting that some boaters run at WOT and recommend it. I guess I'm never too old to learn. I'm not an outboard mechanic so I will yield to their experience and appreciate their opinions. But it drives me crazy to push a piece of machinery, with many moving parts, to it's peak revolutions and keep them there for an extended time. On the safety factor -- Call me a fuddy duddy but I never liked to run faster than 30 MPH in an open boat.

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I have the same question on props. right now on my 40 merc. with a 10 3/8 14p and running 4800rpm (5250 max) and looking to go to a 10" 13p 4 blade to bring my RPM back to 5200

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There is a totally different design concept to a two stroke and a four stroke, a lot less moving parts. Actually the valve train is the main limiting factor in how many rpm a four stroke can turn and sustain. A two stroke does not have a valve train.

The two stroke racing guys turn their motors 10,000-11,000+ rpms constantly. The main limiting factor to engine life with a two stroke at high rpm is the rings. A Mercury 2.5 225hp fishing motor turning 6,000 rpm should last over 1,000 hours. That basically same 2.5 300hp factory racing motor turning over 8,000 rpm has a ring life of approx 100 hours.

To a degree, the design of a two stroke engines components (some makes run two piece crank shafts that don't do well with high rpm) will limit how much you can safely turn them, but the main limiting factor for many is how it's ported. The 200hp, 3.0 Johnson has a red line of 6,000 rpm. I take that very same engine, go in with a die grinder and rework the ports, change carburetor's, bypass the rev limiter and can turn that same motor 8,000 rpm all day long, and make close to 350hp. However, that much rpm shortens ring life so I usually don't get as aggressive with the porting, keep it down to about 6,500 rpm and make 325hp, and it will run just about as long as the factory stock motor and get way better fuel economy than it did as a stock 200, and it can probably turn that 6,500 rpm 24/7 if you want to run it that way.

Notice I have been referring to two strokes. I am dumber than dirt on four stroke outboards, since I've never even physically had my hand on one, so I'm not going to say what's good or bad for them.

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It will have better hole shot and probably be a little faster if you did. Go with a good stainless prop and you will probably see a very noticeable difference in it.

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my 190 tx with a 90 opti is great. 23 mph at 3200-3300 rpm or about 8.5 mpg :eyebrows:

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I generally do not run WOT unless it's a tournament start and I know "my" is popular.  Usually I beat the competition due to driving skills, not a fast boat (that's another subject).  But otherwise, I run about 55-60mph, or about 5200-5400 rpms on my 225.

 

My mechanic always tells me I need to run WOT more often because I tend to get more carbon build up on the plugs than normal.  But to me, changing the plugs is a better alternative than an accident at 70mph.  That, plus it's a rougher ride at WOT.

 

Here's information about props and rpms...  http://www.bassresource.com/fishing/props.html

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I generally do not run WOT unless it's a tournament start and I know "my" is popular.  Usually I beat the competition due to driving skills, not a fast boat (that's another subject).  But otherwise, I run about 55-60mph, or about 5200-5400 rpms on my 225.

 

My mechanic always tells me I need to run WOT more often because I tend to get more carbon build up on the plugs than normal.  But to me, changing the plugs is a better alternative than an accident at 70mph.  That, plus it's a rougher ride at WOT.

 

Here's information about props and rpms...  http://www.bassresource.com/fishing/props.html

If carbon is building up on the plugs it is probably building up on the pistons and head which is not good. Ask your mechanic about the results of carbon buildup. He has not told you the hold story. It can cause premature detonation when carbon gets under a piston ring.....Al

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Haha, with a '78 25 HP Johnson and a 14 ft v haul jon with two people I need to keep it WOT if I wanna get anywhere.  I don't mind it.  The old Johnson doesn't seem too either.

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You WOT range is the range you want your engine to be able to turn when running wide open. It ensures your engine won't be lugging excessively throughout it's RPM range causing excessive wear and causing the engine to work harder than it has to. Usually you want to prop your motor so it's running near the top end of your WOT RPM range when your boat is at a normal load.

X2!!! Having the right prop is key to getting the best from your outboard..

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