4 strokes at WOT

[Flex]

Hi all.

I haven't had much to do with 4 strokes. I have always been a 2 stroke fan for simplicity reasons.

My question is using 4 strokes at WOT (or close to). Take yamaha 50 2 stroke and 4 stroke as example.

Both outboards produce 50hp at around 5000-5500 revs which is pretty much WOT.

Now i know you can run 2 strokes for 24hours straight at WOT and not have any problems at all with it..

But going by how a 4 stroke works, wouldn't running them close to max revs eventually blow the thing up? I would have thought 4 strokes like cars. You dont run your car in the redline at all(or only for a few seconds) or it'll blow up.as you have cam shafts,valves etc all trying to align at 5000-6000revs. where 2 strokes dont have this problem.

[PADDLES]

all engines can be made to operate best at different rpm ranges, it just depends on the mechanical design.

from what i can see, modern outboard 4s engines incorporate a lot of technology (close tolerances and balancing in manufacture, variable intake lengths, variable valve timing etc.) that allow them to rev really well.

that being said though, i would also think that extended running at full throttle would wear a motor out quicker than operating it at a lower rpm. this would happen whether it's a 2s or a 4s. remember that the 2s will give more power for a given rev range than a 4s but it'll do it less efficiently.

[Kiktz]

Can some one please tell this idiot what wot is?

Cheers Aj

[PADDLES]

sheesh aj .................. which one of us is the idiot? me or flex?

[finga]

wide open throttle :)

Mate, you would not be the only 'goose' as many others probably didn't know but were too afraid to ask.
Remember there's never a silly question just a silly response ;)

Cheers Scott

[finga]

I think AJ was referring to himself

[PADDLES]

thanx finga, i thought he was referring to one of us and was wondering why. lol.

you're right though, "no such thing as a stupid question"

[FNQCairns]

Flex, it doesn't matter what the marine engine is, the higher in the RPM range it exists at (time) the lower it's service life in total hours.

4 stroke outboards exist by the exact same rules as 4 stroke car engines, the longer and closer they are to redline the shorter their life on average there is no way around it the physics has not changed, tolerances have not changed, neither in relative terms has the materials over 15-20 years but the interlectual understanding to produce highly efficient mass produced components eg induction and exhaust flow advances, because of this and sump oil specification advances has allowed the engines of today to in effect do it easier at redline than engines of the past.

2 strokes do not like to rev....per say, they like to rev with a relatively light load hense the reason proping is so important in 2 strokes, any 2 stroke modern or old tech. 4 strokes can handle poor proping abuse better although they are suseptable to carboning up when abused for hundreds of hours, still overproping/overloading in a 4 stroke will cause the identical recipricating/linear part wear as it would have in an old FJ holden grey motor - the parts they share in common of coarse, which is most of them, in name but not number.

Advances in oil has certainly helped make the 4 stroke marine engine what it is today, tcw3 has not done the same for 2 strokes, it is too low of a grade and really only just able, well not even just able but it's the best oil regulated for use in marine 2 strokes.

cheers fnq

[ozscott]

WOT is not redline.

Cheers

PS. Modern 4s are not like a car motor and are designed to rev out and stay there - well balanced, low friction, strong etc, which is partly why they are so expensive.

Cheers

[saurian]

Flex , sounds like a 2v's 4 stroke argument coming up ????
I would warm a 4 stroke up before giving it to it.
Other than that can't really see the drama of wide open throttle in a recreational form , and yeh mechanical things wear out .
Maybe more regular oil changes would help, but if it is designed to run to
a certain rev range at wot, run to that rev range.
I have , no dramas.
Ta.

[Roughasguts]

I run my Honda 4 stroke at what for hours at a time.
It's either flat stick or idle no in between.



Mind you it is only a lawn mower.
And to be honest not a very bloody good one.

[finga]

WOT is not redline.

Cheers

PS. Modern 4s are not like a car motor and are designed to rev out and stay there - well balanced, low friction, strong etc, which is partly why they are so expensive.

Cheers
So maybe a silly question but here goes....
If the throttle is wide open and the outboard is in gear how do you get to redline if no more throttle is available??
Confused Scott :-/

[finga]

I run my Honda 4 stroke at what for hours at a time.
It's either flat stick or idle no in between.



Mind you it is only a lawn mower.
And to be honest not a very bloody good one.

At least you have a lawn you bragger. ;)
Ours does an excellent imitation of a quarry :'(

[Roughasguts]

Yeah sorry finga should of mentioned it's up for sale.
Can't see it being used ever again, unless for re-arranging rocks.

Loved me lawn mowing, it kept the wife and kids away from me.
Was even equipt with a stubby holder.

[charleville]

I have had my 60 HP 4 stroke merc running at 6000 RPM on occasion just to see what it will do.


...BUT, one of the few remaining fragments of knowledge that my memory has of doing a metallurgy subject in my engineering degree course a hundred or so years ago (ok well, maybe thirty or so but it seems like a hundred;D ) was that the more reversals that a bit of steel endured, and the more stress that you put it under, the quicker that it would fatigue.

Accordingly, I run my donk at mostly 2/3 WOT, maybe a bit higher than that when I am impatient which, regrettably, is frequent - but I would never run it at WOT all the time.

This is especially as I want ten years out of this donk without trouble. Am half way there as of last week. 8-)

[saurian]

Hey finga , where is the redline on boat gauges ?????
Sounds like car or motorbike gauges to me not boat.
Ta.

[ozscott]

The redline of an engine is the max revs that the manufacturer reccomends running it to (before it blows with some grace!!!). The WOT is where with normal load the boat is proped so that it will rev to the reccomended WOT range which for motors I have had is usually between 4500 and 5500 rpm - ie less and the boat is overpropped - ie too big or too much pitch (or both of course) throwing stress on the gudgeon pins etc because the engine is labouring (partic 2 strokes because they dont like to labour at lower revs) and if you can exceed the range with normal load then its underpropped meaning that the prop is too small or the pitch is too light on.

Just have a look at the manufactuers specs.

Cheers

[ozscott]

ohh..if you want to know how high the real redline is just stick it in the water with no prop at all and open the taps - watch the tacho and when a rod comes out the side of the power head mark the tach then do a re-build...

[finga]

Hey finga , where is the redline on boat gauges ?????
Sounds like car or motorbike gauges to me not boat.
Ta.
I know my old Merc hasn't a redline on the taco so what's the difference between redline (or max. recommended rpm) and WOT in a boat?
On this yammi the red line is where you see the redline ;)
You mentioned previously that redline isn't WOT. So what's the difference??

Cheers :)

[ozscott]

8-) ohh..if you want to know how high the real redline is just stick it in the water with no prop at all and open the taps - watch the tacho and when a rod comes out the side of the power head mark the tach then do a re-build...

[Kerry]

Rule of thumb for 4 stroke outboards utilized by normal people under normal everyday operating conditions is never exceed 80% of WOT.

[ozscott]

As I understand things mate - Wide open throttle is maximum throttle that you can give it - but that does not mean that the revs achieved is the redline (max reccomended revs) of the engine, for the reasons that I set out above..hope that helps mate.

[FNQCairns]

Redline is where the engine has reached it's peak of HP and torque and will start grading off. So in a car no use reving past in gear as you will get better power to the ground if you change gears before that stage.

In a boat even though it has no redline marked it is still the point the engine constricts it's hp and torque. This will usually be somewher after manufacturers operating range if history has any bearing although each model is an individual even in the same brand, new engines with computer controlled modules anything the geek types into the softwear could be the redline.

I suspect most 4 strokes run right on or at the redline at WOT in an effort to produce a better torque and hp curve in the lower ranges so it feels more like a 2 stroke in response.

cheers fnq

[leezor]

Rule of thumb for 4 stroke outboards utilized by normal people under normal everyday operating conditions is never exceed 80% of WOT.

Don't recall reading that in my operators manual, only time it mentions not to run at WOT is during the break in period.

Kerry, are you referring to at 80% RPM the engine delivers the most efficient torque?

Lee

[ozscott]

HP max is always at higher revs than torque max

[Flex]

Thanks for the response guys. As i said i haven't had much to do with 4 strokes. But I wouldn't mind upgrading to one eventually. I just wasn;t sure if 4 stroke outboards were manufactured differently or meant to run alot different to say a car.

I realise all engines wear out the harder you rev them. But I was lying in bed one night and thought how my car doesn't like being revved past 5000rpm much. feels like its gunna explode..lol

And I figured a 2 stroke would handle prolonged higher revvs more efficiently as there is no belts,valves,cams etc.

But I must be wrong in my theory somewhere, as i know most big boat owners use 4 strokes now and seem to run em for hours on end at WOT with no problems.

Maybe time to save some money for a 4 stroke:)

[Roughasguts]

Redline, may not be at Wot.

If your boat is over propped.
Or over loaded it would still go WOT,or flat stick. But may not get any where near the Redline, or Max RPM recomended by the manufacturer.

But if the hull jumps over the top of a wave for a moment, it sure will reach above and beyond Redline.

[Kiktz]

Cheers Finga,

Paddles was refering to myself, as i dnt know you to comment.

AJ

[DR]

i thought outboards had some kind of govenor on them to stop you from over revving & this could be removed or adjusted if required?????:)


could have been in a dream;Dwas it??

[leezor]

The rev limiter on my DF225 wont allow it to rev above 6100 RPM, this should be the case with all EFI engines.

[ozscott]

not all - the older ones didnt.

[leezor]

Thats bizarre, maybe they where relying on valve bounce to limit the revs ;)
Or maybe the manufacturer had plenty of confidence they would hold up to over reving.

[ozscott]

My 93 Yammy does not have a limiter. I had a 99 model 60 merc that did - it also had a shallow water drive setting that allowed you to raise up past full out trim to the tilt section and then to power up to 1800 rpm, after that it auto retracted the leg back to max trim!!! It worked too. It had a brain...yey!

[bdm56]

My 2002 50hp Merc has both an electronic rev limiter and a system which won't allow the tilt gear to lift the leg out of the water above 2000rpm.

Good safety points and both work :)