What determines longevity of a street eng. over a track engine, (if any)

[H.G.P.]

Only for Porsche engines (not transmisssions, suspensions, etc.,),....

what determines the life of a street Porsche engine over a track Porsche engine?

Do I take a higher risk in running my new (broken in) rebuilt on the track (vs. the street)?

Thanks

[widebody911]

Stress / time

On the track, engines are driven higher, harder and faster than on the street.

[H.G.P.]

Originally posted by widebody911
Stress / time

On the track, engines are driven higher, harder and faster than on the street.

I'm wondering if that is actually good or not for a car built to race. Whether such things, if possible, such as carbon getting blown out is an advantage, .....

........and what part of the engine itself gets stressed the most over say a "street" engine. (Porsche only)?

Thanks

[randywebb]

there is always friction....

[H.G.P.]

I'm starting to think with my average total miles per day, back and forth from work sites in the Porsche, only about 8 miles, it might be considered to take the car to the track?

[Wayne 962]

It has to do with the way the engines are built. The rule in racing is maximum HP and lightest weight. That means running everything as close to the edge as possible, which means more wear and higher heat, etc... Usually also higher compression.

Running a street engine on the track shouldn't hurt it one bit...

-Wayne

[ficke]

I think it would also have to do with the way you drive on the street and track also. Some people bounce off the rev. limiter on every shift on the track, some lug the engine on the street, Turbo motor sometime come right off the freeway to a rest stop and shut off immediately so the owner can go use the facility same owner on the track will let it idle before shut down, go figure. 911 engines have cooling and lubricating systems that or not taxed on the street ,big safety margin that is not used some time on the track in street cars to Porsche spec. It does not abuse a Porsche engine to be driven on a track but you can abuse a Porsche engine on and off the track, Oh yeah smoked clutched by people who do not know how to drive in traffic on the street. not warming up, and , and and........I'll just stop.

[ricochet]

Forgive me if I'm wrong in this generalization, but "speed kills" is what I always lived by. Not just speed in MPH but also RPMs. I understand lugging a motor is terrible, but also high RPMs cause more wear, correct?
You guys know much more than me, but I was taught to look at RPMs like money in the bank, spend too much/too many and the bank runs dry.
If wrong, I apologize, but this has been my lesson learned 40 years ago (with American cars). I also accept lugging a Porsche motor will quickly kill it much quicker than high RPMs.
Believe me, I love high speeds and high RPMs, so I am not damning either, but have accepted both bring higher risks, possibly shorter lives.
Wouldn't a high revved motor live a somewhat shorter lived, than a well taken care of non-abused motor? I run all my vehicles farely hard, but try to avoid the red-line and near redline if not needed. I keep those for when needed, kinda like money in the bank (too often needed for the p-car).


I re-read this thread and now I question my stuff. I regularly run my p-car at 3000-5000 RPMs with no fear, try to not push 5000 unless wanting a grin or needing acceleration for freeways,etc... but will push her to 6500+ sometimes (my Carrera rev limit is 6800).

Track use should be ok if I stay within the 6500? With good oil and everything else in check are you guys saying this will not hurt these engines? I'm in a learning curve here, and trying to make my p-car last.

I thought high RPMs (5k+) caused much accelerated wear (my dad took me up often in light aircraft <60's> back then treated high RPMs as bad). Forgive me, I am feeding off this thread.

[ficke]

There is no metal to metal contact on bearings and as long as you stay with in the design limits of the component's the metal fatigue is not a real issue. Some components have I would guess so many revolutions in them but good oil might play more of a role in their life expectancy. Starting an engine does more damage to bearings for instance than red line rpms. Running a engine within its power band is what it was desgined for and to not do that is wasteful and has no real benefit in my opinion.

[randywebb]

not bearings -- rings

[jluetjen]

There is no metal to metal contact on bearings and as long as you stay with in the design limits of the component's the metal fatigue is not a real issue.

I agree with your points and disagree with your conclusions.

1) Yes, there is genereally no metal to metal contact on the bearings. But that doesn't mean that there isn't wear. Even oil can have some degree of erosive effect which is why bearings will wear out. It's not a question of if (unless you throw engines away at 50K-100K miles), but rather when. At the sustained higher rev's encountered on a race track, this erosion happens faster, not to mention the forces that the bearing systems encounter have to deal with the higher inertial loads which tend to go up exponentially. So a 500 RPM increase in rev's can have more then a 500/6500 RPM impact on bearing wear.

2) Metal fatigue most likely won't be in issue unless parts are poorly designed or you drastically overstress them. But that doesn't mean that plastic deformation isn't an issue. Rods will routinely stretch (and not return) from normal wear. This is why rods usually have to be reconditioned when an engine is rebuilt. Failure to do so (recondition or rebuild) will result in the big ends deforming which will mean that the bearings will start to loose oil pressure which increases the likelhood of metal to metal contact. Add in the affects of bearing wear and your loss of oil pressure will increase further.

3) Then there is just general wear and tolerance build-up in the chains and other systems and you'll find that things start to drift out of spec.

All of this stuff increases with rev's. In general terms an engine has so many revolutions in it. You can use them up at 3000 RPM's on the street or at 6000 RPM's on the track. Things wear out faster then 2x3000 RPM's at 6000 RPM because inertia increases exponentially.

[Formerly Steve Wilkinson]

My engine, as modified, has a 7,500-rpm rev limit. On the track, I rarely take it over 6,000 and then only to 6,500. Of course I'm not racing, just doing DEs and TracQuest stuff, but since Paul Newman's about the only racer older than me, that's quite enough.

Stephan

[Grady Clay]

More is expected from a track engine than a street engine. On
the street your engine is only occasionally run at full potential.
Most don’t notice slight decline on performance. On track you
are demanding 10/10 all the time and when someone can pull
you down a straight, you notice.

Race engines are rebuilt far more often in order to keep the
performance as close to 10/10 as possible. Since they
constantly run at high stress the rebuilds also serve as a safety
factor to prevent malfunctions.

A street engine taken on track is not stressed as a race engine
so long as the revs stay within normal limits – not bouncing off
the rev-limiter or put in the wrong gear.

To answer your question: Does track time reduce the life of your
engine? Not appreciably if everything was in good order to start with.

An early 911 (’65-’89) has an advantage over Porsche engineers.
It is the benefit of hindsight. You can build a better 911 engine
now than when it was new. All the slightest weak points have
been found during the 15-40 years of early 911 operation and
racing. The difference is the original engine was built from ALL
new parts. In rebuilding an engine you must use good judgment
as to how much to replace with new. An engine with only new
bearing shells, rings, and valve guides is not the same as a
proper (and more expensive) rebuild.

Most important is the reason we own these cars. They are a
trackable street car or conversely a streetable track car. Yes it
takes some special effort to own and drive a cool car like the 911
in all these situations.



For many, the 911 IS the center of the automotive universe.
This Vinn diagram is great for talking about cars.
You can use it with just 911s or Porsches.
You can include all automobiles.

Best,
Grady

[donstevens]

I like Grady's reasoning. A Street driven car with occasional track use will show no appreciable extra wear. Porsches were designed to be driven hard so occasional blasts to redline are not going to hurt a thing. Think about the way the Germans drive on the street. They are on the redline all the time.

I also like what Ficke has to say. It is all about reasonable usage.

If you boil all of these points down though, there are so many varibales to consider (not the least of which is the "touch" of the driver) that there is no definitive answer to the question "do track driven engines wear faster?"

Relative to H.G.P.'s question "Do I take a higher risk in running my new (broken in) rebuilt on the track (vs. the street)?" The answer is yes, you do take a higher risk running the car on the track simply because the risk of a damaging over rev is higher than during street use. Also the risk that the engine may over heat and cause some damage is higher. However, as long as you don't abuse the car and/or make any mistakes, the wear attributed to the track vs. street will be imperceptible for the life of the engine.

Drive it like you stole it.

Don

[randywebb]

richochet - here is my Sunday exposition in more detail than above:

First, I don't think you will have any problem at all if you redline the properly maintained & tuned engine frequently on the street. It will still last for 1, 2, or maybe 3, hundred thousand miles.

The two places I think will wear the fastest are the valve seats and the rings and their grooves. The vlaves smash down with a lot of impact force onto the seats. The newer seats are better but that is a lot of force over and over. The guides have been weak points (rel. to other places in the engine). The valves are not pushed exactly straight up and down by the rockers; instead they are at an angle. The rockers seem to last well themselves.

The rings are exposed to combustion temperatures and products, just like the valves. The rings are not going to get the same oil film as the bearings. As the rings are pushed up and down against the groove, they will eventually wear the faces of the groove that they ride in. The force vectors here are also at an angle, so there can be differential wear (if you give the pistons and rings to a metrologist).

Bottom line - those are some of the "weak" points in the engine.

Again, running the engine hard won't hurt it to any appreciable degree. Warm it up, don't lug it, and avoid cold starts (tho it is functional for short grocery getting trips, that is the worst time for an engine , as pointed out above).

You are more likely to have external components break than the internals. And the risk of loss from accident or theft is probably nearly the same as internal damage on these very strong engines.

[Chuck Moreland]

Lot's of good info here. What I will add is that a street engine used on the track will see reduced life if the oil temp is not kept in control.

Most street 911s have inadequate oil cooling capacity for track duty. Usually not a problem for a few DEs, but it is something that should be addressed urgently for any car that sees regular track duty.

Excessive temp thins the oil and it looses its ability to provide protection, hydrodynamic lubrication breaks down and the engine wears rapidly because metal-to-metal contact happens.

[ricochet]

Thanks H.G.P. and all of ya for offering information. My 79-84 911 bastard car has no known past, but the leakdown and evaluation gave me info saying she is healthy. I plan to D.E. sometime soon, now I feel more confident. I'll run the pee out of her and not feel bad, she is designed for it after all.
Was helpfull guys and H.G.P. I apologize for asking questions on yer thread, but think we both got answers to your questions. Great info for free. Is a great place.

[Dantilla]

Airplane engines are limited to lower RPMs because propellor efficiency drops off dramatically as soon as the tips hit transonic speeds.

2700 is a very typical redline.

[Grady Clay]

I will second Chuck’s admonition in spades. In hot weather not only does a 911 need a substantial full fin front cooler with a fan and ducting but also changed to the 1.82:1 engine fan ratio. Here in Colorado every sensible person additionally uses the “Rubbermaid Solution.”

Keeping the engine and coolers’ fins clean is also absolutely necessary.

Best,
Grady