BruseLee - The racecar analogy is lame and inaccurate. Stop using it. True race engines are built for top performance, not reliability or longevity. They are higher compression, have aggresive cam profiles, have aggressive timing. Run low additive high octane fuels, have astronomical red lines. All this leads to more HP and short life. It is not just running at high RPM that makes them grenade.

LB, very true. The Porsche owner's manual does a very good job telling owners how to brake-in a new car & engine.

<4,200 RPM's for the first 2,000 miles is the "key" one.

My prediction: a post will arrive shortly telling us that the proper way to break in an engine is to "drive it like you stole it." They will support that with "my friend is an engine builder" story.

These posts CAN get somewhat predictable.
:D

BTW- the advice on limiting revs on break in has been around since I was a kid, a very long time indeed.

Must be somthing to it. hard to believe the car makers want to have their engines inplode.

The analogy is still apt. At what RPM do these guys make all that HP? Well, up near red line.

Read the title of the thread again. The contention here is that running your box up at very high RPMs is GOOD FOR THE CAR!

That simply can't be substantiated by good physics or engineering.

It might be good for the driver (it is very much fun) but I simply don't like sloppy thinking.

I am not suggesting anyone drive around town and lug the motor nor not run the car at whatever RPM they want.

I am suggesting that they get real. Running the car at 5000 RPM plus is not doing your engine a world of good. It is not a muscle, it does NOT get stronger with use.

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.

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).

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.

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?

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.

:D

Interesting
 

Please remind me never to buy a used Porsche from you :)

I am planning to keep my car well past 200,000 miles as I cannot afford a newer or new one. So this attitude doesn't work for me from any angle.

My 2.5 motor only lasted 79k, and measuring the condition of the car when I got it at 82k, those were 79k hard miles. It appears that all the maintenance was done on the car too from records I've come across. The new motor (not reconditioned) that was put in the car and only had a couple of thousand miles on it now has 25k after three years of spirited weekend driving.

I replaced the tranny two years ago for suspect noises in 1st and 2nd gear at low rpm.

I would not be surprised if during my ownership of this car, with meticulous maintenance and replacement of every single thing I can find that is wearing or worn, I will have to put a third motor in it. Of course, it will be a 3.4 or 3.6, but nevertheless, I might not get 200k out of this new motor with the intermediate shaft failures that still occur in newer Porsche engines.

Paul, you have a good attitude about your car... it is indeed a rich man's toy for sure!
I drive my car like I stole it a lot of the time and run it up to redline most every time I put the key in the ignition. I just don't keep it above 4,000 rpm all the time because I want to keep my existing motor running for at least another 100,000 miles.

I think there's two schools of thought about sports car ownership. Those like yourself who enjoy the car to its full limits and might be harder on the motor than one who buys a car to own for 20+ years. I'm that second kind of guy by virtue of my personal financial situation and my growing satisfaction of fixing up an old car that has my fingerprints on most every part of the car as the years go by.

I guess my take on this thread is this: The motor is designed to be revved right up to redline and it does blow carbon out of the motor ... and the sound is glorious at redline. Conversely, if one keeps the revs up all the time, he or she will be replacing the motor sooner than later.

Guys,
Didn't we do this whole engine load/rpm/excessive wear thing a couple of months ago??
http://www.986forum.com/forums/showthread.php?t=14724

i just redline a couple times a day to keep the engine clean

I agree and do the same except I see no issue with running the car above 4000 rpms IF IT"S IN TOP GEAR (in my case 5th).

Couple of interesting posts from performance forum
 

Posted by NITRO on July 03, 1998 at 09:24:41:

In reading your question, you have answered it with your research.


Regarding friction and wear, once again, you answered the question. If pistons travel at higher speed/ crank revolution, the amount of wear is greater. The anti friction composites we're now using help some, but T.O.O. also has another saying: Everything mechanical will eventually wear out and break.


The most common rod failures we've experienced over the years have always taken place on the "overlap" cycle, where the piston is traveling up at high velocities, with no compression up-top, and when the rod tries to slow the piston as it nears TDC, the rod goes, the piston pin can go, and the pin will sometimes pull the bosses out of the piston, or all of the above.


You're (simply) dealing with Mass x Velocity (squared). Now, examine the figures. Both mass and velocity are the players, but wich one is squared? = Velocity.
Regardless of rod ratio or any other player, the greater the RPM the higher the velocities, which = "ruined peoples motors".
What you like (regarding high rpm power), and what your engine likes are two different things.

If you ask any engine in the world if it enjoys running at high rpm = max. Q or stress, everyone of them will tell you they don't like it, unless one has a death wish or something.

T.O.O.'ll probably be around to better answer your question, but I gaurantee that he'll touch on the same items, and he talks to engines as well, that's how he makes them do what he wants, although he does write their genetic codes in the pre-build engineering.



--------------------------------------------------------------------------------

RPM's are nice...they are our friend

--------------------------------------------------------------------------------

Posted by 82'Rolla on July 03, 1998 at 06:21:24:

I love the sound of a high revver as well. Unfortunately to make your engine do this, it must be very well guarded against the added stress.


"*Maximum piston acceleration is approximately 8,000g which
puts a load of over 3 tons on each connecting rod."

This is where a lot of the damage comes from, and it increases non-linearly, not sure if it's exponential, plus the fact that the piston actually travels further. The stresses that your engine endures by raising the rpm's by 1000rpms is much worse than increasing boost by 10psi.


I suppose if you start out with the intentions of building a high revver, and compensate accordingly, it can be reliably done, but it sure will get expensive...Carillo rods ain't cheap.

I think it was Louis (deVirgilio sp?)from honda-perf who was also looking at this at some time, and noted the differences in the internal construction of the engines in relation to it's revability.Posted some nice articles, I think I still have them.

Ted

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.

What's your more rigorous method alternative?

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.

Again, there is a lubricant at work here that doesn't act as you appear to expect it to.

Again, engines under high stress wear out faster. It's not RPM related, it's stress related.

From Diesel website.
 

Ecopower
The Valtra N111 EcoPower model offers fuel savings of 10-15 percent by lowering the engine speed. The average piston speed is 20 percent
slower than in regular engines. The lifespan of the engine is correspondingly extended. Wet cylinder liners and intercooling also extend the lifespan of
SisuDiesel engines. In practice, the Valtra N111 EcoPower model means significantly lower workhour costs, environmental friendliness and low
emissions. An added benefit is the reduction in engine noise by 4-5 decibels.

Engine wear and economy are two totally different things. Slower motion definitely decreases the energy required to move the parts around. I'd like to see the proof here of extended engine life.

Why is the average piston speed of the 849 Sleeper important??

One of the biggest factors that engine builders use to predict engine reliability is “average piston speed”. In short, the peak rpm and stoke length are plugged into a formula to obtain the average piston speed in “feet per minute” (it’s a finer measurement than mph). Here are The numbers:

Stroke Length
68mm SuperJet
74mm Kaw750/800
SXR Setups

Stock OEM peak rpm
6150 rpm
6550 rpm


Piston speed @ stock RPMs
2742
3180
SXR stock

Piston peed @ 6800 rpm
3032
3301


Piston peed @ 7000 rpm
3122
3398
849 Sleeper

Piston peed @ 7200 rpm
3211
3495


Piston peed @ 7300 rpm
3255
3609


Piston peed @ 7400 rpm
3300
3592
Wet-Pipe

Piston peed @ 7500 rpm
3345
3641


Piston peed @ 7600 rpm
3390
3689


Piston peed @ 7700 rpm
3434
3738
Dry-Pipe




4000+ fpm – Completely unpredictable life span of crankshaft components

3700 fpm – Crank life can predictably be 20-35 hours

3500 fpm – Crank life can predictably be a full season of use

3300 fpm – Crank life is predictably 2-3 seasons of use

3100 fpm – Production unit range, predictably 4-5 seasons of use



It is common knowledge, among stand up racers, that modified SuperJets have considerably better crankshaft life than modified SXRs …. Average piston speed is the reason why. One of the best features of the 849 Sleeper is that it delivers the water-speeds of a high revving setup, but yields the significantly lower piston speeds that improve crank life. It’s true that the slightly increased weight of the 849 Sleeper pistons does slightly increase loads on the connecting rods. However that load increase is nowhere near the load increases subjected by the extra 400-700 rpms of the higher revving race pipe setups.

Remember the title of this post. The contention is that driving at higher RPMs (and by def. higher piston speeds) is GOOD for your car, ie your car will thank you.

The burden of proof is to show how high RPM driving is GOOD for your car.

I have shown evidence that it is not. Find me some expert evidence that high piston speeds are GOOD for your car.

Again, the engine is NOT a muscle. It does not improve under stress.

I don't have to prove the negative.

:D

Brucelee, what's the source of failure in this case? Is something breaking from stress or is it breaking from wearing out? I would bet that it's the former. You have to look at the cause for this to be useful information.

That is not the issue under discussion. The issue is, is running at high RPMS GOOD for your car.

That was the contection.

Show me proof that it is GOOD for your engine.

Thanks

:)

Question-If running your car at high RPMs were GOOD for your car, why is this condition considered as "severe service" by most manufacturers and generates a recommendation for more frequent oil changes.

If it were GOOD for your engine, they should tell you to run the oil a lot longer. RIGHT?

Anybody know the stroke of a 2.7?


Mean piston speed =0.167 x Stroke in inches x 7200 rpms.