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Discussion Starter · #1 ·
The question has been asked in another thread with different topic by Kelowna, concern was about high r.p.m. for extended periods, so I guess it will help to open a new thread with proper title.

To share actual experience: This weekend I ran my JK 2009 with 5000 r.p.m. for more than 20 minutes continously in 4 LO range 6th gear at 80 km/h on extended subkha area, with outside temperature of 48 deg C. The engine temp. remained in mid-range and I had no issues.

My only possibly relevant mod is an AEM Brute Force cold air intake.
 

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Internet Owner
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Is there a question in there somewhere?
If it is: Will it hurt my engine? the answer is no, provided your engine has been well maintained and has no issues like bad main bearings, etc...
5K is not red line or even yellow. Your temp was constant and I'm assuming you kept an eye on your oil pressure too.
If you had bad vibrations or strange sounds or smoke coming out of the exhaust, yeah it's cooking.
But no, continuous 5K rpm will not harm a good motor.
Is that where you were going with this?.
 

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I am not to worried about it myself. If it were that bad for motors then boats would have transmission with more then one gear.
 

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What about you gears?? I've seen guys cook gears in muscle cars doing high rpm long duration runs. ( should add they were crazy ratios like 5 something, can't remember exact)
 

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Discussion Starter · #6 ·
@RikRotorhead: No, it was not a question, I feel confident,
just wanted to share positive experience with someone who had doubts.

@08Rescue: I run the stock ring & pinon ratio (is it 3.54 ?). I know few guys
change it to 4.56 or 4.88 with 33" tyres like mine. I also hear that changing the
R&P ratio often results in early damage, don't know if this is attributable
to workmanship. The R&P adjustment seems to be a quite delicate job.
The workshop I use clearly state that they have less or more difficulties
with different makes of R&P.
 

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Why would it matter where the engine was made?
Engines come in a huge variety. Some are designed to run best at high rpm, others at low rpm.
But if you do not run up into the yellow or red you can run them constant at high rpm for days, provided they are lubricated and cooled properly.
Airplane engines run at a constant high rpm, generators, tractors, etc...
Race engines are designed to run at extremely high rpms for long periods of time, some up around 12K or more, but they usually run several very small pistons and huge oil coolers.
 

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Where do I get one of those?! I have to hold mine or it just falls to the ground!
 

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That was my point in asking, as I have never had an issue with sustained high rpm running. Just yesterday even we took a run a long way down the lake to see a lift that is for sale, and back home. To get on plane I always use full throttle, and once up do throttle back, depends how much though, and yesterday it was very little, as I just wanted to get there, and back. So it ran about a half hour each way, at just under wide open.
 

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I made a little helicopter for mine.

Sweet! Is there a weedwhacker forum where I can go to get modding ideas like that? And are you a mod on that one too?
 

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That was my point in asking, as I have never had an issue with sustained high rpm running. Just yesterday even we took a run a long way down the lake to see a lift that is for sale, and back home. To get on plane I always use full throttle, and once up do throttle back, depends how much though, and yesterday it was very little, as I just wanted to get there, and back. So it ran about a half hour each way, at just under wide open.
Engines have a power curve. The curve peaks at the best efficiency rpm. If you hook it to a dyno you will see where it is.
If you throttle up to plane, once it planes it has less resistance and you can throttle back to best efficiency rpm. Better economy happens there. Most people don't have a clue where the peak is on the power curve of their boat engine.
 

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My boat did not come with a manual, the owners lost it. But what I can find to read says it should run at a max rpm of 5,000 but it actually excedes that when lightly loaded, which is fine with me, because then when its loaded up, and I still want to ski, it can pull me up well. Yesterday with full petrol and eleven people onboard it peaked at about exactly 5,000 rpm, and I throttled back to around 4,600 to 4,700 for a nice high cruise speed. If not in a hurry, just going for a leisurely cruise with my sweetie, we run in the low to mid 3K's. Adding nine more people drastically hurts its time to get on plane I do know that. Also I should paint over the metal plate that says max. 9 people. :)
 

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My fishing boat has a Mercury outboard, but no tachometer.
Also I'm unsure what rpm range it is supposed to be at as a maximum number anywayS. I just use full throttle until it is planing, then by ear, throttle back to what sounds like a "Happy" rpm for it. The gauges that boat does have, are so grossly inaccurate they are best ignored anywayS.
 

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I am surprised you get 5k out of the 5.0. I have the same motor but different outdrive in my boat but mine is carbed and I hit WOT at about 4,000 RPM at 51 MPH in the same size boat. What prop do you have on there?
 
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