RPMs vs longevity

I'm expecting to get a wide variety of opinions on this question. I have a degree in Mechanical Engineering among others. I know that ultimately the lifetime of anything that experiences friction and vibration will have only so many cycles. (That's why they replace components routinely in aircraft). I also know that loading on bearing surfaces puts stress on them and also hastens their failures. So it seems to me that when I read here to "drive it like you stole it" cannot be accurate. As a piston moves up and down in its sleeve, it is, ultimately, going to wear itself out. So that suggests that unnecessary RPMs should hasten the wear of those components. Also engine design will create "sweet spots" in the operating range of an engine. You can actually feel it in most cars - when the engine seems to operate a little bit smoother - less vibration. Conversely, "lugging" an engine - puts additional stress on bearing surfaces, connecting rods, crankshafts, etc. So my training suggests that the way to get the longest life out of your engine is to drive it with as little stress at the lowest RPMs you can. (and all the accompanying things - like fresh oil, etc). For our 996s, I'm guessing RPMs somewhere between 3000 and 4500 rpm should provide maximum engine life. There is a reason that racing engines - which operate near the top end of their RPM range, don't last very long. When you get near red line, the stress on the operating components (pistons, connecting rods, crankshaft, camshaft, etc) are literally shaking and vibrating themselves into oblivion. The predecessors of the 911, the 356'es, would flatten out the roller cams if you "lugged" them. That's the origin of the expression: "keep the revs up". But they were talking about 2500 rpm (and not 1500 rpm) - not 5000 or 7000 rpm.

Is this a statement or question? If so, yes, you are correct

I completely agree with your posting. Correct in every way. I do not track my car but non the less bring the revs up to 4-5000 revs on occasion in the lower gears to get my Adrenalin rush so to speak. Normal driving for me is from 22000 to 2800 with the changing of gears activating around 3000 to 4000 revs. I am happy at 25000 normal cruising with a 3000 on motorways or freeways in 6th bringing 80 mph. Third gear and higher revs gives me a great Adrenalin rush around the Amish twisty lanes. Dry surfaces. The compression of these engines is amazing which saves on brake wear. So I suppose it's a hit and miss situation when the cars gears are used in the correct way. I am not afraid of using the gears all the way from 6th down to 2nd in preference to the brakes. I love the sounds of the engine when dropping from 3rd into 2nd gear at 3000 revs on entering an estate side road. I don't think I have ever hit the red line. No need for high revs unless you are on the tracks.

"Drive it like you stole it" is to raise oil pressure, basic rule of thumb there is 10psi per 1000 rpm to overcome centrifical force of the spinning crankshaft throws trying to prevent oil flow to connecting rods. M96/97 engines should cruise in a range to minimize load on the IMSB. Cylinder wall loading is mainly dependent upon rod/stroke ratio & rod length. Maximum rpm is usually determined by connecting rod strength since the highest internal force is @ TDC & BDC when the crankshaft throw reverses direction & expects the rod to follow!

Agree, that's why my Jeep 4.0 will never really wear out... =)

Once warmed up higher revs equates to higher oil pressure which will help force the oil into places where friction is a problem in a high enough volume to do some good. When we talk about driving it like you stole it I don't think anyone is intending for you to redline it constantly. We are talking about keeping the revs well out of the lugging range, keeping the oil pressure elevated, kicking the vario system on, and generally just enjoying the car rather than treating it like it is porcelain. So yeah, 3-5k is a good normal range with the occasional romp in the higher range.

Well, there's the old favorite "Drive it like the Dr. intended" that gets bandied about, which I think is not equivalent to "drive it like you stole it." Driving it like you stole it implies that you don't care about the car because it's disposable...and even though the 996 can be cheap to obtain, I don't think that many of us treat them as throw-aways. This car was designed to be a sports car - it makes good power across a range of several thousand RPM. I believe that I drive my car "as intended" - which means staying in the power band and actually driving the car like a sports car, taking advantage of its power, handling, braking, etc. I'm not trying desperately to wear it out, but if I wanted a car that I could drive like a diesel, I would have bought a diesel. Good torque at low RPM, highway cruising at low RPM, all just as Hurdi describes it, can be done quite nicely in an old diesel Mercedes. There is no shortage of evidence that pushing a machine hard reduces its lifespan. There are formulas to help you anticipate how much more quickly a machine will fail when used at various percentages of total capacity. If you run at 100% all the time, you're going to tear it apart in short order, regardless of whether the machine in question is a Porsche, or a washing machine, or a blender. I understand that some people are very concerned about longevity and want their Porsche to last a very long time. I get this philosophy - you see the car as a thing of beauty and want to prolong its life as much as possible. I also understand that there are people who want to wring every last shred of performance out of their Porsche, and they're willing to accept that doing so may be expensive. Every one of us falls somewhere along the continuum between these two mindsets. I'm on the "faster!" end of the scale; Hurdi and MikeAndNancy might not be. *shrug* That's the cool thing about these cars - they can putter along in the right lane and look amazing; they can also tear-*** along a winding mountain road or dive into a corner on a track and look amazing.

So I guess the old italian tune up is a big no no?

The Cuban grind (where you get towed around the parking riding on a head to resurface it) is also discouraged.

Thought that was the Puerto Rican grind...

Race engines are completely different. They are not only driven differently, but are designed differently. In an effort to shed weight, individual components aren't designed with an endurance limit. Race engines are arguably disposable, so parts are designed for x amount of cyclic loads. To compare an engine designed for x years to x races is completely useless. An 'optimum' RPM range has more to do with journal bearing design and a few other parameters. Fluid film pressure and nodes will change angles with shaft RPM, fluid viscosity and temperature, but journal and shaft geometric play a large role in pressures and nodes. With how much the bearings wears, and manufacturing tolerances, your sweet spot can be rather dynamic depending on how old the engine is and the condition of your oil. This is where oil degradation and fluid load capacity will make all the difference in engine performance and longevity. If you want to know the science behind how materials wear and how surfaces interact, get yourself a book on tribology. Comparing apples and oranges might get you in the right direction, but you're still just as ignorant. To get the longest life out of your engine, you need to know how to maintain your engine. A particular driving style may shorten your maintenance intervals, but that doesn't necessarily kill your engine. Neglect kills more engines than one's driving style ever has.

Interestingly, Mr. Arrogant Pants, the only use of the term "race" or "race engine" was by you - so maybe throttle back on schooling us all for being wrong on a point nobody made.

I think your conclusions as a result of your ME degree are right on. The engine is attempting to fling itself apart while running, and the faster it's run the more it tries to fling itself apart. The rod bolts are holding it together so that it doesn't spray steel bits around. The more force you apply to that rod bolt the more pressure it is put under. Same can be said of the lubed bearings and journals. I drive the 996 rather gently although I keep it moving down the road well. Usually I'll short shift or skip shift once warmed up just to keep things from being worked hard. Aviation piston engines last from 1200-2400 hours of operation before recommended overhaul(generally not required). Geared engines which have higher redlines usually have lower TBO hours, due in some part to piston swept travel over time, and exh valve cycles. So, there's clearly a correlation. It's my opinion that a properly maintained, and cared for 996 engine should go 250k miles before any kind of loss of materials will require complete rebuild. This does NOT include catastrophic faults/failures like casting porosity, D chunk, or IMSB. I have several cars now with +200k miles on them and they are running fine, because I take care of my equipment. My 1999 Durango is a backup car with 267k, and it barely uses any oil between changes. The high gear is getting a bit sketchy to shift up when warm, but once selected, it'll stay there. Needs a band adjustment, I"m just too lazy to drop the pan and do it.

My Acura is now nearing 220k miles. Gets redlined at every opportunity when warmed up. Car sits at 4000+ RPM for 10+ miles at a time every time I drive to snowbowl when climbing the I-17. I've never babied the car, and it gets driven aggressively all the time. Longevity is unaffected.

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By me, and by OP. Re-read the post.

I like my car it seems to go best when it sounds sweetest... When it sounds sweetest it seems to live longest... Happy Days

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1. Without knowing how long the engine would last with gentler driving, you cannot say that longevity is not affected 2. It may have gone 220k miles, but what is the condition of the engine? How much power has it lost? Whats the condition of the bearings? It may not have failed yet, but who knows what condition it is in.

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But it could also have died of boredom in exactly the opposite way.

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okie dokie. I'm guessing it has feelings also?

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No its a car... The point is there is no definable end, no right or wrong, the OP suggests this as they lit the blue paper and retired a safe distance.. It is easy to slow drive an engine to death my mother in law does it on a family hatch 1250cc its clogged up, chocked up and chucks out so much crud when its taken up to anything above 5000 revs it is as I say dying from boredom.. In human terms the heart attack waiting to happen couch potato.. As you say - quite rightly - the thrashed / high revved car is likely to die from stress Both end up in the same position - in need of repair no right or wrong! OS_R

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I think the point is that for the longest life, you should limit revs, but not to a point where the engine is lugging or experiencing excessive harmonics (which occur at certain rpms). Limited load is also better. That said, we all know thats not why we bought the cars, so you trade off some life (how much is anyone's guess) for the fun of opening the throttle and giving it some rpm. There are extremes at both ends and then the happy medium. anecdotally, My grandfather had an Audi 80 that he would upshift at 1500rpm. Car lasted 200k kilometers and drove reasonably well. It was a bit down on power, but ran relatively smoothly.

I will not own my current car much past 40K miles. I'm fairly certain it will last until then, so I'm not very concerned with the subject. I own my Porsche because of the performance AND the fact it is a tremendous daily driver. It serves 2 wonderful purposes. There are times when it feels sluggish. Usually that's when it had been daily driven far more often than opened up on the freeway. That's always remedied by a few quick on ramp sessions and 75(+)MPH cruises in 4th. Yes, an Italian Tune Up. But it works. Owning a 911 but worrying about engine wear under load is counter productive to the experience. That's why God made Honda Accords...

How about using all of the RPM range? That way you get the advantages of low wear (let's say on the highway you slap it into 6th gear) but around town you run it up to the redline to have some fun with the car? Just like everything else I see moderation as being the key. So by exploring all parts of the tach you're in many ways moderating the use of the engine. I've got 160k on mine and I still drive it as if it only had 30k. Sometimes I hit the redline, other times I shift at 3k RPM - just depends on the situation and whether I want to feel some of the additional power or not.

To the OP, once warmed up it's your car so drive it anyway you want. Personally I find my car most fun to drive between 3,500 - 5,000. I rarely go above 5,000 rpm and not for extended periods of time. Cruising on the highway for a long trip maybe it's sitting at 2,400 rpm. You are probably correct that the sweet spot is 3,000 - 4,000 rpm

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No, it doesn't. Do you honestly think that that your car is building up so much carbon due to daily driving that it is having a noticeable impact on how the car runs? Back when carburetors were popular, cars didn't run as well when cold, at low rpms, and small throttle openings. Hence the italian tune up would work reasonably well. Its placebo on a modern car.

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Well, damn my eyes. I still think your pants are arrogant.

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QC, some folks want to live in the world of "blowing out the carbon" and adding Marvel Mystery Oil. They may or may not carry a rabbit's foot for luck, and it'll be a cold day before you find them stepping on a crack.

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Yea, actually it does. Maybe not from daily driving, but it does. Seen a lot of V12 Maybach's that idle all day because the driver is waiting and wants to wait in comfort. Never pushed because, hey, they are chauffeurs. Comes into the shop later with misfires at idle, rough running, etc. Take the head off a fuel injected V12 that doesnt get pushed at all, with running issues and good fuel, its all carbon. So much so, Mercedes had a special fuel additive. The other part of the repair instructions was an Italian tune up. So, yes, the Italian tune up does work on fuel injection cars.

I'm just trying to fit in

I'd rather lose power than never use it. If I wear it out after 200k miles or more, I'll buy a rebuild or another car.

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Look up the carbon issues with Audi's DFI engines. I still want a B7 RS4 though..

^ IS that a V12 Maybach? You know, there's an additive you can get for that.

Hahaha.....no but the concept is there. Consistently see more trouble with garage queens than the hard drivers. Different engine design though.

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"Can't we all just get along?"

I tend to agree with the OP's theory. The problem is, when I get in the car I can't seem to control my right foot and I end up in the "drive it like you stole it" camp. I think I need professional help.

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Yes it does Oliver. The ECU gets used to a certain pattern of driving. An Italian Tuneup makes the ECU adjust. It's not about the carbon...it's about the silicon.

Hell just do what one of the members does and not drive it at all and it will last forever

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Word...

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One of my employees is a boy racer who loves to speed-shift his "'Teg" - which is boy-racer-speak for his beater Integra. Twice now he has tried to slam the car from 4th to 3rd and hit first gear instead - and in both cases, new engines were required. Curiously, his enormous red shift light doesn't seem to help when he over-revs the car by several thousand RPM. So, if your "style" includes being an absolute idiot, it MIGHT kill more engines than merely being neglectful.

Stupid is as stupid does...

Trust you butt and your right foot. The sweet spot is when the throttle is most efficient and responsive. The engine is happy and you are happy. When you feel it you know it. And you will know when that is not where you want to be, such as stop and go traffic or a long 500 mile stretch of road without a turn in sight. The Variocam Plus is very oil dependent, and low oil pressure and supply (level) can combine to cause expensive unpleasantness. Unless you are drag racing there is no logical reason to mash your foot to the floor from a standing start in first gear and winding it out to seven grand. That said I did own an Alfa Romeo Giulietta Spider Veloce and stock from the factory the 1290 cc engine went to 8000 rpm. The tach didn't even move until 2000 rpm. The sweet spot came in about 4,500 to 4,800 rpm and it stayed to north of 7000. I raced it for three years, never shifted under 7000. The motor was bone stock except for playing with the jets on the Webers. But apples and oranges...the Italians think differently than the Germans.

Is this the op?

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Totally different. Direct injection engines have carbon buildup largely due to there being no fuel sprayed over the intake ports and valves to keep them carbon free. M96 motor is still port fuel injected. In experience, most modern automotive motors will suffer a major mechanical failure from abuse or flaw/defect before actually wearing out. Assuming the rest of the car/chassis lasts that long

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Help for the tarded plz. If there is no fuel passing through the intake ports or over the back of the intake valves and the gas charge is injected on the comp stroke with intake valve closed then burned then expelled then on the next intake stroke it has a vacuum pulling in and down more clean air, how is carbon getting there?

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My comment was in regaurd to another comment stating modern engines cant have performance issues due to carbon build up. I wasn't making a comparison to the M96.

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Exhaust Gas Recirculation, Internal valve overlap, crankcase vapors, etc. there are plenty of places for unburned hydrocarbons and oil and other deposits to come from.

This is fodder for the gray faced bean counters... Not the driversownerspromulgatorsandmembers of the greatest motorsport fraternity autodom has ever known... maintain them well because it's interesting fascinating and fun..drive them to getsqueezeextract the maximum pleasure and joy... and someday, if necessary set them free and get another one, because this will perpetuate the manufacturing of new and better ones... .. I'm sure some of you will open fire on me as the newbie... but my need to be loved is rather low anyway, (I get lots at home) blessings...

*slow clap*

Love me some Dwight...