Is it safe to run my engine wide open throttle?

[nokiddin]

The other day I went out tubing and found myself wanting to run full throttle all the time while pulling people on the tube, I guess I really wanted to dump them. I have a 1984 Mercury 90 hp in line six 2 stroke, on an 18 ft starcraft holiday. I got to thinkin if it is safe for my motor to be running WOT for a whole tubing run ( 5 - 10 min or so) or am I gonna kill my engine?

Can anyone fill this newbie in?

 

[BonairII]

Re: Is it safe to run my engine wide open throttle?

As long as your correctly propped and running within manufacturers recommended rpm range..........you can run WOT all day long if you want.

 

[CV16]

Re: Is it safe to run my engine wide open throttle?

I think most will agree on here that these motors like WOT better than lugging them all day. Just be sure you stay in the max range and you'll be fine. My problem is I feel I lug mine too much pulling tubes and knee boards.

 

[BonairII]

Re: Is it safe to run my engine wide open throttle?

My problem is I feel I lug mine too much pulling tubes and knee boards.

Go down a couple inches in pitch. I have a 15 for pulling tubes/heavy loads and a 17 for regular running.

 

[nokiddin]

Re: Is it safe to run my engine wide open throttle?

Anyone have the max range for my engine?

 

[444]

Re: Is it safe to run my engine wide open throttle?

I would probably aim for 5200rpm, though I thin the max rated rpm for that engine likely is around 5500. I had a 15' glastron with an 84 merc 90hp inline 6 and I ran it at full throttle all the time. I've got an 82 merc 175hp v6 and run it on extended full throttle runs all the time. These 2-strokes were made to be wound out.

 

[Texasmark]

Re: Is it safe to run my engine wide open throttle?

Anyone have the max range for my engine?

Yeah.............whatever she will take! I had an '88 115 hp tower on a Ranger pad boat and I ran 6000 consistently for over 7 years and BIL is still doing it today. And as CV 16 said, they like to run. If you don't have a tach, she will sing to you when she is up where you want her.

Mark

 

[carholme]

Re: Is it safe to run my engine wide open throttle?

1984 90 inline 6 cylinder:

Models 90&900 90/4500-5000

http://web.ebscohost.com/serrc/pdf?...3-91c3-90b85f34e2db@sessionmgr11&vid=4&hid=19

Gerry

 

[Texasmark]

Re: Is it safe to run my engine wide open throttle?

1984 90 inline 6 cylinder:

Models 90&900 90/4500-5000

http://web.ebscohost.com/serrc/pdf?...3-91c3-90b85f34e2db@sessionmgr11&vid=4&hid=19

Gerry

Heads up on this answer!!!!! This 90 is a choked down 115. Back in the day they ran a different ratio lower unit and were advertised to be load haulers rather than high performance engines.......had to say something to separated it from it's big brother. It's not that it won't run up there it's just not setup to run up there....carb jets, timing setup, outside chance some porting changes but I'd really doubt that. Otherwise it would have a 115 badge on it. So don't worry about it.

Mark

 

[redjmp]

Re: Is it safe to run my engine wide open throttle?

Those motors will run all day at 5500 but you are decreasing its life.
Yes they are designed for running at wot but running any engine at its redline will reduce its life expectancy.
I have heard others say to run at wot for shorter periods and cruise at 4200.
Personally I like to run mine for best economy at 3050 and put the hammer down from time to time for some thrills.
Now if you are pulling a tube, they are only rated for about 20mph max so you should not be anywhere near your redline.
In fact you shouldn't be turning anymore than about 3500 or you are putting your tubers in harms way.

 

[BonairII]

Re: Is it safe to run my engine wide open throttle?

Those motors will run all day at 5500 but you are decreasing its life.
Yes they are designed for running at wot but running any engine at its redline will reduce its life expectancy.

I don't believe running a motor at max manufacturer recommended rpm is actually "redlining" it (but I may be wrong).

Regardless, I haven't heard of a single motor ever "wearing out". 99.9999% of engine failures are caused by poor maintenance, lugging, lack of oil, cooling etc

 

[jimmbo]

Re: Is it safe to run my engine wide open throttle?

The inline 6 90hp had a rpm range of 4500-5000. It had the same 2:1 gear ratio as all inline 6s from 1978 till 1988. How it was different from the 115s; different carbs, fewer reeds, smaller and lower ports. These engines were stump pullers with great low end torque and holeshot. They just ran out of breath above 5000 due to the porting.

 

[redjmp]

Re: Is it safe to run my engine wide open throttle?

Basic engineering laws of squares say that on a motor that turns say 20% faster from 5 to 6 k increases its internal inertial forces by 44%.
Since all metals fatigue and eventually fail proportionally to the amount of force x the time exposed to such force, it stands to reason that running any engine at a higher rpm will increase the rate of fatigue on the internal components and cause accelerated wear and therefore diminishing its longevity.
That is why when you rebuild an engine, you always check tolerances on everything. Because parts wear out.And they wear out proportionally to the amount of force exerted on them.
Airframes are retired after a certain amount of airtime because of this fatigue.

 

[BonairII]

Re: Is it safe to run my engine wide open throttle?

Basic engineering laws of squares say that on a motor that turns say 20% faster from 5 to 6 k increases its internal inertial forces by 44%.
Since all metals fatigue and eventually fail proportionally to the amount of force x the time exposed to such force, it stands to reason that running any engine at a higher rpm will increase the rate of fatigue on the internal components and cause accelerated wear and therefore diminishing its longevity.
That is why when you rebuild and engine, you always check tolerances on everything. Because parts wear out.And they wear out proportionally to the amount of force exerted on them.
Airframes are retired after a certain amount of airtime because of this fatigue.

I understand what you're saying, but it's still my contention that it takes A LOT of hours at WOT to wear out a 2-stroke....many more hours than most people own their motors.

 

[hotrod53]

Re: Is it safe to run my engine wide open throttle?

In a perfect world, assuming proper cooling and lubrication, it all comes down to numbers. If a ring is designed to last (hypothetically) 1 million strokes, running it faster just puts more cycles on the parts and therefore gets you more strokes closer to the end of its life. Throw in the fact that you're sucking in more air, passing more fuel thru the system, and depending on an electronic part to last, the likelyhood of failure at higher RPMs increases.

 

[444]

Re: Is it safe to run my engine wide open throttle?

Airframes are made weak to save on weight and are subjected to totally different forces than an engine block.

Rarely does a 2-stroke outboard fail due to normal wear and tear like running at 5000 rpm. It's usually a catastrophic failure of some kind from some other completely unrelated cause. I've never heard of an outboard throwing a rod through the block just because it wore out or rings being completely shot just because they're worn out from use while getting proper care and maintenance. Usually is some other problem like a clog or defect in the fuel system causes the engine to lean out and boom. Or an oil supply failure or overheating due to a cooling system failure, etc. Some of it is due to poor maintenance, too many guys just put gas in and go. Modify the engine to spin faster and/or put out more power than the manufacturer intended, then you are pushing the edge. However I would not be afraid to run an engine within the limits of what the manufacturer intended.

For an adult, 20mph on a tube can be pretty boring. I will admit to exceeding this speed at times!

 

[Texasmark]

Re: Is it safe to run my engine wide open throttle?

I don't believe running a motor at max manufacturer recommended rpm is actually "redlining" it (but I may be wrong).

Regardless, I haven't heard of a single motor ever "wearing out". 99.9999% of engine failures are caused by poor maintenance, lugging, lack of oil, cooling etc

Ditto on both counts. The '88 Merc I mentioned is a testimony to that as are all the '50's and '60's still running without block overhauls and you know those lower hp engines ran WOT most of the time.

On redlining, my engine, '02 90 hp loop charged triple, 5500 is the upper limit, got away from me one day while I was replacing some linkage my engine ran away on it's own, ignition switch had nothing to do with shutting down the engine. My Quicksilver tach maxed at 7000. I hard pegged the tach so I have no idea just what my actual rpm's were but the engine continued to run on it's own for several minutes. I haven't torn it down to see just what was what, but I still run it and it still pushes my boat up at the 50 mark and I still run my usual 5600-5800 rpms like I did before. Have heard those suckers will run 10k on racers.

Mark

 

[Texasmark]

Re: Is it safe to run my engine wide open throttle?

I understand what you're saying, but it's still my contention that it takes A LOT of hours at WOT to wear out a 2-stroke....many more hours than most people own their motors.

Ditto.

Along the same lines you always have people wanting the "best this and the best that" It really doesn't matter if you keep things in perspective. You will probably sell your whatever before you ever get close to wearing it out, or die first.

On stresses, I am close to a flight path to DFW airport. Back when I was working, the MD 82 aircraft was an old airplane. That was 8 years ago. In watching most of the aircraft coming into this AA hub, most are 82s or a variant of that airframe.

So thinking about alum work hardening and not tolerating flexing like steel, and I know they use a special alloy, but still it IS alum, all the 10,000s of flexure these skins have seen and still are intact, even if they aren't stressed continuously above their yield point.

My 2c,
Mark

 

[chum1]

Re: Is it safe to run my engine wide open throttle?

Built the sheetmetal/structure cockpit of the md 88 in long beach a long time ago back in 86', QC was pretty good except for repair from the occasional UAW heroin addict screwups, lots oF AA planes.

Like any engine running full power just because its rated is dumb and burns extra gas, i can see pulling a load or skier, something were you need it, or the occasional drag race but just cruising along pegged adds extra possibilities for failure.

 

[leach0369]

Re: Is it safe to run my engine wide open throttle?

20mph is boring thats why we go 35mph so when you hit the water it stings a little... Boy's will be Boy's but I will admit faster is better...

Airframes are made weak to save on weight and are subjected to totally different forces than an engine block.

Rarely does a 2-stroke outboard fail due to normal wear and tear like running at 5000 rpm. It's usually a catastrophic failure of some kind from some other completely unrelated cause. I've never heard of an outboard throwing a rod through the block just because it wore out or rings being completely shot just because they're worn out from use while getting proper care and maintenance. Usually is some other problem like a clog or defect in the fuel system causes the engine to lean out and boom. Or an oil supply failure or overheating due to a cooling system failure, etc. Some of it is due to poor maintenance, too many guys just put gas in and go. Modify the engine to spin faster and/or put out more power than the manufacturer intended, then you are pushing the edge. However I would not be afraid to run an engine within the limits of what the manufacturer intended.

For an adult, 20mph on a tube can be pretty boring. I will admit to exceeding this speed at times!