2009 Porsche 997

[T Bone]

Originally Posted by footie

TB,

Find me another example of this apart form the 944Turbo. As Bruce said a design fault at best, I have had numerous turbo models and I haven't heard of head gaskets being a problem before this.

The stresses at high rev are far more problematic to engines than at low revs, think of the weight the piston is at 8000rpm compared to 1500rpm and you will know what I mean.

Sorry TB but you are beating a die horse on this one and no one is coming to your defence.

I don't need someone to come to my defence my friend. In fact, I would want you on the other side

I am not disputing that high revs, high load stresses engines. Low revs, high loads cause a specific type of stress. Having an explosion and dissipating it at lower rpms will cause more stress on stuff like the headgasket, connecting rods, crank....

Let's not forget the original issue for discussion, people who try to accelerate in a broad speed range in one gear....not only is it lazy but not too good for the engine either.

I have blowned headgaskets on 944 Turbos...with closed deck designs, the headstuds are alot more effective. This is personal experience that I can relay.

This is also not a slam dunk issue as some people think....here are some discussions (on a quick google search)

Here is an excerpt from a like minded fellow:

http://www.subaruforester.org/vbulle...04/#post408179

==========
Lets see if I can explain this.

As stated lugging is the result of too much engine load for a given rpm. As for what is going on in the engine I will limit our discussion to just the compression stroke and power stroke. Lugging applies to any internal combustion engine 2 stroke, 4 stroke.....(links for reference)
4 stroke Four-stroke engine - Wikipedia, the free encyclopedia
2 stroke Two-stroke engine - Wikipedia, the free encyclopedia

In normal operation on the compression stroke the piston compresses the air/fuel(A/F) mixture as the piston travels upward when the piston/crank shaft is at say 32 degrees(a common timing) before top dead center(TDC) the spark plug ignites the A/F mix causing it to explode and expand. The speed and momentum of the piston, connecting rod and crankshaft are able to over come this and the piston continues on its quest to reach and pass TDC, at which point the piston then moves downward on the power stroke making use of the energy released by the exploding A/F mix.

When you are lugging an engine, the piston, rod and crankshaft are barley able to overcome the ignition of the fuel air mixture. This results in the piston being pushed back down, thus pushing the rod down. Meanwhile the crankshaft still has rotational inertia trying to drive the rod and piston upwards. In that brief moment of the piston and rod being driven down by the expanding gases and the crankshaft still in rotation the oil that is buffering the rod bearing from the journal of the crankshaft is squeezed out, the rod bearing and the journal make metal to metal contact. Which is the sound you hear and what you feel is the engine fighting its self. There is some more to what is going on but this should be enough to scare you. Doing this basically creates the same chain of events as detonation due to ignition advance, poor fuel or excessive compression.

Long term negative effects.
1. Prematurely worn rod bearings and crankshaft.
2. Poor oil pressure as a result of excessive rod bearing clearances.
3. It is possible you could spin a rod bearing when it contacts the journal.
4. If done excessively you can weaken and break a crankshaft, rod or a piston.
5. It also places undo stress on the head gaskets.

Here are some poor images of damaged bearings.
Examples of Engine Bearing Failures

Much of this type of damage is visible on tear down and inspection of engine components. On engines with roller type rod/crank bearings this shows up as flat spots or burnelling on the rollers and or race. The recreational power sports industry see many engine rebuilds caused by this. ATVs used as work horses(plows, pulling...), motorcycles(primarily cruisers) where the owners do a lot of low rpm cruising(45-55mph) in a high gear and rarely changes gears. Sadly when you confront them about their riding style and habits while showing them the damaged parts and explaining what happened, most of them will argue that you are wrong. The heavier the load the more rpms are needed to keep you from lugging the engine. So a solo 160lb motorcycle rider may be able to get by with going 45mph in 5th gear at 2200rpm with out lugging the engine. If that rider adds a 150lb passenger they will have to down shift to 4th and be at say 2800rpm to avoid lugging it and maintain 45mph.

Hope that helps explain it.===============

http://www.subaruforester.org/vbulle...-engine-35404/

http://www.mx6.com/forums/2g-mx6-gen...tml#post409678

http://www.thedieselstop.com/forums/...67/index1.html

[bruce.augenstein@comcast.]

Originally Posted by T Bone

Ha! I don't think we will agree here but I will make my point one more time. Under load, particularly with FI, the explosion is disperse over a longer period of time because of the low rpms putting more stress on the components...

Can we at least agree that the amount of actual time that the cylinders are under pressure is identical regardless of whether the pressure waves are happening 10 times per second, or 30 times per second with each pressure wave lasting for one third of the time?

Can we further agree that max cylinder pressures are at max torque, and not at very low rpm?

Bruce

[footie]

TB,

This is the wonder of the internet and the downers of it, I am not going to google search what I already know. That is that high revs cause far and a way more problems than low revs and that is my argument, you feel high revs is better and less stressful on the engine and I just happen to disagree.

[T Bone]

Originally Posted by bruce.augenstein@comcast.

Can we at least agree that the amount of actual time that the cylinders are under pressure is identical regardless of whether the pressure waves are happening 10 times per second, or 30 times per second with each pressure wave lasting for one third of the time?

Can we further agree that max cylinder pressures are at max torque, and not at very low rpm?

Bruce

Bruce, I think we are talking about seperate issues. I am talking about the stresses place on the engine in a single firing of one cylinder, whereas, you are talking about an engine operating over a period of time.

In a single firing of one cylinder, the explosion of the air-fuel charge is dissipated over a over a longer period of time. Assuming the same charge, an engine at 2000 rpm vs 6000 rpm, the engine at 6000 rpm dissipates the explosion 3X as quickly. This means the sustained force on the various parts of the components is felt for a lot shorter period of time in the high rpm engine.

Now if we add time into the equation as you propose, the overall stress may be the same but the individual stress per firing is lower for the high rpm engine.

I would agree that low rpm engines cannot get enough air for max torque since the max volumetric efficiency will be higher in the rpm band. Even at a lower torque loading, the stressed caused by the lugging is still really bad.

[bruce.augenstein@comcast.]

Originally Posted by T Bone

This is also not a slam dunk issue as some people think....here are some discussions (on a quick google search)

Here is an excerpt from a like minded fellow:

That is yet another of the really ignorant positions people take, either on the net, garages, racetracks or bar rooms.

The key and fatal flaw is that the quoted poster assumes max spark advance at minimal rpm, which is ridiculous. The entire reason for a spark curve is to tailor combustion pressures to make best mechanical use of cylinder pressures at whatever rpm. The other flaw is that the poster ignores the fact that cylinder pressures are always lower at low rpm, like every other incorrect poster on the subject.

Sheesh!

Bruce

[bruce.augenstein@comcast.]

Originally Posted by T Bone

Bruce, I think we are talking about seperate issues. I am talking about the stresses place on the engine in a single firing of one cylinder, whereas, you are talking about an engine operating over a period of time.

In a single firing of one cylinder, the explosion of the air-fuel charge is dissipated over a over a longer period of time. Assuming the same charge, an engine at 2000 rpm vs 6000 rpm, the engine at 6000 rpm dissipates the explosion 3X as quickly. This means the sustained force on the various parts of the components is felt for a lot shorter period of time in the high rpm engine.

Now if we add time into the equation as you propose, the overall stress may be the same but the individual stress per firing is lower for the high rpm engine.

I would agree that low rpm engines cannot get enough air for max torque since the max volumetric efficiency will be higher in the rpm band. Even at a lower torque loading, the stressed caused by the lugging is still really bad.

OK, now that you've agreed that the overall stress is the same, and that there is less cylinder pressure (less torque) at low rpm, your original argument is now completely gone - like everyone else who claims low-rpm, high-load use kills an engine, compared to high-rpm, high-torque use.

Bruce

Edit: PS - As long as it's not pinging (rare nowadays, with such fine control of mixture and automatic timing adjustments), accelerating hard from any engine speed to any other speed (up to redline) will cause no undue wear or damage.

[T Bone]

Originally Posted by bruce.augenstein@comcast.

OK, now that you've agreed that the overall stress is the same, and that there is less cylinder pressure (less torque) at low rpm, your original argument is now completely gone - like everyone else who claims low-rpm, high-load use kills an engine, compared to high-rpm, high-torque use.

Bruce

Actually no. The overall stress on the system is the same but that is actually irrelevant to this discussion. You have not considered the effects of applying force over a longer period of time (i.e. single cylinder firing).

PLease refute the detrimental effects of applying force over a longer period of time.

The issue is lugging an engine because people think it is a good thing instead of shifting gears.

PS. Responding to your PS about everything is good if the engine doesn't ping... Unless the engine is made of steel or some other elastic metal (i.e. so long as you are within a range of stress, steel will return to its original form), excess force over time will fatigue any other non-elastic metal like aluminum.

[dechoong]

Originally Posted by devo

Yes, the current tt can out run the GTR even without PDK. The new engine alone will just add distance. Add PDK and the new tt will walk the GTR.

There is speculation that Porsche may abandon the 3.6l for the 3.8l. However, one thing that is certain is that PAG will cease production of the current GT1 block, which has been race proven for years. Although, many diehards are upset by this, I welcome the updated engine. Time will tell if it is as over-engineered as the current GT1, but even if it's not, it will certainly be stout enough to handle more that the engine's power output. How much power the new block will handle remains to be seen. I have heard that the current GT1 block can safely handle over 700 hp. If one did not intend to heavily mod the new tt, the next generation block should be a better choice.

These launch control dual clutch transmission runs are meaningless to me. I will opt for the standard standard; pun intended. In-gear runs are so much more important to me. The new tt should be heaven to drive.

You should be looking at the updated 997tt if in-gear acceleration is that important to you. The updated 997S won't "come alive" till past 4000rpm.

[lucid]

Originally Posted by T Bone

PS. Responding to your PS about everything is good if the engine doesn't ping... Unless the engine is made of steel or some other elastic metal (i.e. so long as you are within a range of stress, steel will return to its original form), excess force over time will fatigue any other non-elastic metal like aluminum.

T-Bone, you've got this one wrong. Both steel an aluminum will experience elastic and plastic deformation. If you load them beyond their yield stresses, they will deform plastically and will not return to their original dimensions when unloaded. If you don't load them beyond their yield stresses, they will experience elastic deformation and will return to their original dimensions when unloaded. On the other hand, brittle materials such as carbon fiber do not experience plastic deformation and simply fail instead. The key difference between aluminum and steel, apart from their respective yield stresses, is that aluminum does not have a well defined yield stress, and that is approximated by using an offset strain calculation.

If you don't believe me, take a long narrow aluminum pole. Fix one end of it. Gently push down on the other (unsupported) end. It will deflect slightly. When you let go, it will go back to its original shape without any permanent deformation. That's elastic deformation. Also, you can observe the wings of an aircraft elastically deflect when loaded.

Fatigue failure is a different issue. That is what happens to a material when it is repeatedly loaded below, even well below, its yield stress.

[lucid]

Originally Posted by shift@red

The GT3 is the same way curve-wise as the 911, it has the same tq rating as the m3 but FEELS MUCH more tq'y even though the tq curve isnt flat throughout.

Of course, the GT3 feels more torquey than the M3; how much does it weigh compared to the M3? What you end up feeling is not tq at the shaft, but tq at the wheels/vehicle weight. I haven't done that calculation, but I bet it is higher for the GT3 and its lighter weight is a huge factor.

Also, there are subjective issues with how torquey a car feels. By definition, a car with an uneven torque curve will "feel" more torquey, since you will be jerked around more.

[bruce.augenstein@comcast.]

Originally Posted by T Bone

...PLease refute the detrimental effects of applying force over a longer period of time...

Well, I will in a minute, but of course you're not applying force over a longer period of time - just for a longer period of time per revolution. This is exactly offset by having more revolutions per unit of time, with less time for each force cycle.

This is pretty basic, T Bone.

OK, unless the force is destructive, the amount of time it's applied is immaterial. You're saying that an engine making 200 HP at, say, 6000 rpm will wear out (or destruct) more quickly than an engine making 200 HP at 12,000 rpm.

That's nonsense. I'm only bothering with this discussion so that other folks don't get the wrong idea.

I remember awhile back (maybe 15 years or so), a Chevrolet engineer published an SAE paper on this, claiming there were no measurable or discernible effects from even extended lugging, as long as preignition wasn't involved. He got some press out of that, I can tell you.

Bruce

[T Bone]

Originally Posted by bruce.augenstein@comcast.

Well, I will in a minute, but of course you're not applying force over a longer period of time - just for a longer period of time per revolution. This is exactly offset by having more revolutions per unit of time, with less time for each force cycle.

This is pretty basic, T Bone.

I remember awhile back (maybe 15 years or so), a Chevrolet engineer published an SAE paper on this, claiming there were no measurable or discernible effects from even extended lugging, as long as preignition wasn't involved. He got some press out of that, I can tell you.

Bruce

We are obviously not on the same page. Are you now saying yes the engine components experience more strees for low rpm, high load situations? If yes is then your argument that it doesn't matter / immaterial?

If this is what you are saying then I don't think we are far off. The difference is covered by the design of engine and materials used for there to show wear.

BTW, I would love to read the paper....

Originally Posted by lucid

T-Bone, you've got this one wrong. Both steel an aluminum will experience elastic and plastic deformation. If you load them beyond their yield stresses, they will deform plastically and will not return to their original dimensions when unloaded.

Yes, I exaggerated....steel is 3X more elastic than aluminum...and the key is to keep the forces below permanent deformation

http://www.engineersedge.com/manufac..._materials.htm

[footie]

The wonder of the Internet, anyone with the knowledge of how to work believes they are an expert.

Can you explain why VAG make more turbo units than anyone else and yet this problem isn't arising anywhere near the amount that you are trying to tell is the case. Sorry TB but you are so wrong it's not even funny now.

More engine problems happen under extreme stress, the kind that only happens near maximum revs. Can I ask you, how long do you believe an M5 engine will last at maximum revs in 6th gear.......................it's not that long I can tell you.

[T Bone]

Originally Posted by footie

The wonder of the Internet, anyone with the knowledge of how to work believes they are an expert.

Can you explain why VAG make more turbo units than anyone else and yet this problem isn't arising anywhere near the amount that you are trying to tell is the case. Sorry TB but you are so wrong it's not even funny now.

More engine problems happen under extreme stress, the kind that only happens near maximum revs. Can I ask you, how long do you believe an M5 engine will last at maximum revs in 6th gear.......................it's not that long I can tell you.

Nice emotional post with no supporting arguments mate.

I will use a standard fanboi argument to debate this issue at this level...

VAG turbo motors rarely fail because they don't make any power....not like the 335i BOOOIIII !!! Thank You.

I honestly don't understand why people love to get emotional over debates.... I could be wrong, other people can be wrong. Be civil and have some good discussions.

[Sticky]

Originally Posted by footie

The wonder of the Internet, anyone with the knowledge of how to work believes they are an expert.

Can you explain why VAG make more turbo units than anyone else and yet this problem isn't arising anywhere near the amount that you are trying to tell is the case. Sorry TB but you are so wrong it's not even funny now.

More engine problems happen under extreme stress, the kind that only happens near maximum revs. Can I ask you, how long do you believe an M5 engine will last at maximum revs in 6th gear.......................it's not that long I can tell you.

Nah, M motors last forever damn it! As a matter of fact, in the interest of reliability, I believe everyone should raise their redline by a few thousand revs and keep the engine there at all times. Especially when sitting in traffic or drive thru windows.

Could have sworn I read BMW backed the revs down in the v10 in the interest of longevity

[footie]

Originally Posted by Sticky

Nah, M motors last forever damn it! As a matter of fact, in the interest of reliability, I believe everyone should raise their redline by a few thousand revs and keep the engine there at all times. Especially when sitting in traffic or drive thru windows.

Could have sworn I read BMW backed the revs down in the v10 in the interest of longevity

Yeah, the reality is that high revs greatly reduce the life span of an engine. How many Ferraris do you know that have covered 100,000 miles without major engine work.

High revs put far and a way more stress on any engine than putting from low revs and TB should sit back and think about what he is writting and how his comments are making people see him.

[bruce.augenstein@comcast.]

Originally Posted by T Bone

...Are you now saying yes the engine components experience more strees for low rpm, high load situations?...

No. We are still in 100% disagreement. You say low rpm loads are harder on an engine than high rpm loads, thereby leading to the conclusion that an engine with a given amount of power at a low rpm will wear out/self destruct more quickly than a similarly sized engine that makes the same amount of power at a high rpm...

...which is ridiculous.

We don't need to discuss it any further.

Bruce

[swamp2]

Originally Posted by bruce.augenstein@comcast.

You say low rpm loads are harder on an engine than high rpm loads, thereby leading to the conclusion that an engine with a given amount of power at a low rpm will wear out/self destruct more quickly than a similarly sized engine that makes the same amount of power at a high rpm...

Guys, I don't know the answer to this question/debate and am not going to really enter the fray. What I can offer is that you need to think about what are called "load cases" to better debate this topic.

There are loads on various engine components from multiple sources. Two of the primary ones are combustion loads - the periodic, frequency (rpm dependent) loads directly from the mixture combustion. I would think these do peak at the rpm of peak engine torque. The other main type of load is the inertial loads caused by accelerating and decelerating components such as the pistons and rods (really any rotating components but the heavy and long travel ones really make the big loads). These loads as well vary dramatically with rpm just from inertia - they vary with rpm squared. At different engine operating rpms different components will exhibit the feature of being the peak loaded component in the system (or perhaps better stated the peak responding component).

Lastly, the dynamics of components really matters as well. You can't analyze in the "vacuum" of the assumption that parts are all completely rigid and their stress or deflection is determined solely by the load. This is because for a given level of force (applied periodically) the response (deflection and stress) depends on how close you are to any of a components resonant frequencies. Close to any resonances yields much larger loads.

[T Bone]

Originally Posted by bruce.augenstein@comcast.

No. We are still in 100% disagreement. You say low rpm loads are harder on an engine than high rpm loads, thereby leading to the conclusion that an engine with a given amount of power at a low rpm will wear out/self destruct more quickly than a similarly sized engine that makes the same amount of power at a high rpm...

...which is ridiculous.

We don't need to discuss it any further.

Bruce

Did you just have a leap of logic here? Where do I say low rpm / high load is more stressful than high rpm / high load?? This tangent occured when people didn't want to shift, lugging causes is worse than being in the right gear....pretty simple concept.


Judging you by your post, you seem to take a lot discussions personally like somehow I am attacking you by stating an opinion. Relax, it just the internet.

[bruce.augenstein@comcast.]

Originally Posted by T Bone

Did you just have a leap of logic here? Where do I say low rpm / high load is more stressful than high rpm / high load?? This tangent occured when people didn't want to shift, lugging causes is worse than being in the right gear....pretty simple concept.


Judging you by your post, you seem to take a lot discussions personally like somehow I am attacking you by stating an opinion. Relax, it just the internet.

What started this off is you saying:

"People don't realize high load, low rpm (i.e. stepping on the gas in low rpms) is really bad on engines. This leads to premature head gasket failure.

So get off your butts and shift before you step on it. (this is why I don't care about low end torque)."

If this isn't saying that that low rpm/high load is tougher than high rpm/high load, what does?

I never got the feeling you were attacking, but it's obvious you are firm in your obviously incorrect belief, so why bother to knock anymore when there's nobody home on this issue?

Bruce

[T Bone]

Originally Posted by bruce.augenstein@comcast.

What started this off is you saying:

"People don't realize high load, low rpm (i.e. stepping on the gas in low rpms) is really bad on engines. This leads to premature head gasket failure.

So get off your butts and shift before you step on it. (this is why I don't care about low end torque)."

If this isn't saying that that low rpm/high load is tougher than high rpm/high load, what does?

I never got the feeling you were attacking, but it's obvious you are firm in your obviously incorrect belief, so why bother to knock anymore when there's nobody home on this issue?

Bruce

Bruce, where is the relative trade off between high load / low rpm and high load / high rpm?? There is a leap of logic here...

The issue is far from the black and right as you portray. And when you cannot get others to agree with you, you pack up your toys and leave the pram.

Relax man....discussion / debate is healthy.

[bruce.augenstein@comcast.]

Originally Posted by T Bone

Bruce, where is the relative trade off between high load / low rpm and high load / high rpm?? There is a leap of logic here...

The issue is far from the black and right as you portray. And when you cannot get others to agree with you, you pack up your toys and leave the pram.

Relax man....discussion / debate is healthy.

As you may be aware, I have zero problem mixing it up - some might say interminably - with folks who have a differing viewpoint and can actually make a case.

In this case, all you've got is an unshakeable belief that a lower amplitude, lower frequency series of pressure waves is more destructive than a higher amplitude, higher frequency series of pressure waves.

Then you trot out some guy who makes it clear he has no idea what he is talking about - as a proof point!

My position is that, if anything, a higher amplitude, higher frequency series of pressures waves is tougher on the enclosure, but none of it matters if the pressure waves of whatever frequency are within the design limits of the enclosure. The pressure waves in any given engine would be within design limits at any speed as long as there weren't any pressure spikes due to detonation/ping.

So what is there to discuss?

Bruce