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Originally Posted by Brucelee
Well. what you posted is a post from a guy who says he read a report by SAE on engine wear, which was measured by metal part. in the oil. Lets start there.
I agree that wear is greater while the engine is getting to operating temps. I would also agree that wear would be greater under load. ie. hammering the throttle and putting the engine under load. Of course, that is one way and likely the most frequent way that most of us GET TO THOSE HIGH RPMS!
Are you suggesting that we drive our Boxes very gingerly on our way to 6000 RPMS and they leave them there on cruise control? If that is the case, wear would be lower than the classic jack rabbit start. However, at 6000 stress and wear would still be higher than 3000 RPM, all things being equal.
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You said you'd like to see the article, I have provided you with the means to find it. Go to SAE.org and buy it if you're not an SAE member.
I'm not sure that you understand what high load means. It's very easy to accelerate a car to 6000 RPM at light/medium load. If you've ever monitored an engine with a MAP sensor, it's very easy to see.
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Originally Posted by Brucelee
Moreover, the measurement of particulates in the oil is not a very rigorous way to measure "wear" in a classic sense. In fact, one way you can generate more metal in the oil is to change it too frequently (source: Bob is the oil guy).
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What's your more rigorous method alternative?
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Originally Posted by Brucelee
Lastly, if you search this thread, you will find reference to a study on piston ring wear and RPMs. There is a correlation, hard to imagine how there could not be.
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You're not talking about simply rubbing two pieces of metal against each other. There's a non-Newtonian fluid in between the two that has characteristics that can be very counter-intuitive. The viscosity a non-Newtonian fluid changes non-linearly with shear stress, meaning that the faster the two metal parts move relative to each-other, the thicker and more protective it becomes.
There are some very complicated physics going on that are not immediately apparent and often counter-intuitive.
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Originally Posted by Brucelee
Really, the last point. In a reciprocating piston engine, what happens to the forces of stopping and starting a piston throug the cycle as the RPMs increase?
Do the forces increase or not as RPMs increase or decrease or stay the same?
Is "wear" and stress, metal fatigue, bearing wear, reduced at 6000 RPMs or increased vs say at 3000 RPM?
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Again, there is a lubricant at work here that doesn't act as you appear to expect it to.
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Originally Posted by Brucelee
Unless something happened in the universe last night to change physics, I would say that forces are increased at higher RPMs.
Do increased stresses and increased friction rates on metal parts, bearings etc. improve their useful life or decrease it?
PS-Those racing engines are designed to last, ie enhanced casting techniques, allowy metals, six main bearings etc.
They simply grenade anyway. Don't you think the guys would LIKE to get two races out of an engine?
Just a thought.
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Again, engines under high stress wear out faster. It's not RPM related, it's stress related.