porschemikeandnancy

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.

Quadcammer

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

Hurdigurdiman

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.

Byprodriver

"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!

Chiamac

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

gnat

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.

5CHN3LL

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.

dgi 07

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

5CHN3LL

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

dgi 07

Thought that was the Puerto Rican grind...

sweet victory

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.

5CHN3LL

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.

docmirror

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.

Kalashnikov

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.

mharrison