driving below 2800 RPM = trouble?

[CaptainObvious]

That's not very scientific. How is it more difficult for the engine at 2000RPM in 6th gear than 4500RPM in 6th gear, other than at the higher speed there is even more friction to overcome in the engine and from the air resistance of the car moving forward??

If the car couldn't adjust timing or fuel and was detonating before TDC, I can see that being real bad... maybe that's what happened in the good ol' days.

So I can see WOT at 1800RPM not being very exciting, but I don't see how it is bad.

[Steve Tinker]

Think of it as riding a bicycle.
Travelling @ 5mph in your lowest gear your legs will be revolving rapidly - not a lot of pressure on your leg muscles but you will run out of breath & tire quite quickly.
Now try pushing the same bike in top gear @ 5mph - you will probably give yourself a hernia & rupture your knees trying to turn the pedals - thats the same as lugging the engine. With low revs & WO throttle position the load on the lower engine componants (crankshaft, big end bearings & crankshaft main bearings) will be severe.
And don't compare a high compression, high revving sports car engine like a Porsche (who's max torque is @ about 4500rpm) with a diesel engine designed for low rev power who's torque curve is virtually flat from 2000rpm to 5000rpm. They are a different animal all together.

[Lil bastard]

Originally, this thread noted that according to Jake Raby, in essence, operating at low rpms caused IMS failures (or increased the risk of failure).

So far as lugging the engine, there is a definite definition. The British use the term 'Labouring' in the US, it's 'Lugging'.

It means that the rpms have been allowed to fall out of the powerband of the engine for a particular load/selected gear. You are slowly stalling the engine.

An example would be having the transmission in a higher gear than the road speed or load requires, such as not downshifting when going uphill.

When this happens, things heat up very quickly internally and the engine will detonate or ping. This leads to shockwaves in the reciprocating parts (rods, pistons) and the crankshaft, and cause piston slap, scoring of cylinder walls, bearing wear, excess loads on timing gear (chains, belts, gears, or in this case - the intermediate shaft).

In concert with this, because the rpms are low, coolant and oil are not flowing at their optimal rates or pressures further compounding the effects and/or damage.

I agree that theoretically, running the at higher rpms can create more wear. I say theoretically because these higher rpms also allow greater flow and pressures for the oil and coolant which can now better protect against wear.

But, the point here was the IMS. And it is at low rpms that the oil pressure and flow are at such a low point that the inherent weakness of this part is more readily realized - it fails more easily and perhaps more quickly.

Drive it 'harder' and you may take say 10-20k mi. more off the life of your bearings and such over time than if you drove at lower rpms.

I think the point Jake is making though is that by doing so, at least your car will actually reach that kind of mileage, where without it, the IMS will grenade the motor much sooner.

But, I think we need to distinguish between the early cars and the later ones when in '03 Porsche re-designed the IMS.

IMS failure in the early cars is virtually unheard of, in fact, I can't think of a single instance being reported in the pre-'00 cars (though I'm sure there must have been some).

[Perfectlap]

I drove the whole weekend shifting above 5-7K RPM downshifting about oh....300% more. Man this car moves! LOL

[Jaxonalden]

With the weather we had here last weekend, I decided to take out the Box to "teach it the meaning of the word respect". I love that line from Carl the grounds keeper http://www.youtube.com/watch?v=JObTMW3RVf4&feature=related . Anyway, the opposite was true, I forgot just how fast that car can fly and just when I think I'm getting in trouble those big Brembos bring me back to subsonic speeds, I LOVE IT. :dance:

This much fun must be illegal is some Middle Eastern country's.

[renzop]

Could we change the title of this thread to "uninformed opinions maquerading as facts about IMS failures"?

Lugging and almost stalling an engine are not the same thing! Wear to cylinder walls, main bearings, piston rings, etc. does not cause IMS failure therefore arguments that state that high RPM causes wear miss the point.

There was one post early on that tried to give a reasonable (although theoretically only) explanation that links low RPM, variocam and additional force to the IMS that sounded like a good argument for staying on the high side of the variocam switch over point. But that is just a promising theory. Jake Raby's anecdotal evidence that one seriously beaten engine has not had IMS failure supports the theory but certainly does not prove it.

I like the idea of driving your car the way you want and not worrying about IMS. If it blows up then either warranty fixes it, you sell the hulk, or pay Jake. Simple and stress free solution.

[Perfectlap]

^ actually you'd be surprised how many people were unaware of the pitfalls of driving at low RPMs in the wrong conditions. I've been on this forum and others for years and the possibility of this type of driving being linked to IMS failure is seldom if ever discussed unless you follow a more technical forum like Renntech.

I don't think you'll ever prove anything when it comes to these engines... like whether 10K oil change intervals are worse than 7K or letting your oil come up to temp will lead to a longer running engine. There are doubts about everything including Porsche's most recommended oil. Doesn't mean it shouldn't be considered.

[CaptainObvious]

I'm not going to think of this as riding a bicycle, because the amount of torque I can apply at 50 RPM is much greater than the torque I can apply at 200 RPM. If I could apply the same torque at 200 RPM, I'd be stressing my knees just as much, if not more.

And my reference about the 1500 RPM max torque was a BMW 135i which is a turbo charged gas engine. Imagine how "lugged" that car will be all the time. How foolish of them to let the car have any torque below 4000 RPM.

Regarding the cooling, you are burning less fuel at lower RPM and getting more mechanical work per volume of gas burned, so you need less cooling.

At 800 RPM you might be lugging the engine. At 1500 RPM, I don't see how that qualifies with an engine capable of variable timing.

[Lil bastard]

Originally Posted by CaptainObvious

I'm not going to think of this as riding a bicycle, because the amount of torque I can apply at 50 RPM is much greater than the torque I can apply at 200 RPM. If I could apply the same torque at 200 RPM, I'd be stressing my knees just as much, if not more.

And my reference about the 1500 RPM max torque was a BMW 135i which is a turbo charged gas engine. Imagine how "lugged" that car will be all the time. How foolish of them to let the car have any torque below 4000 RPM.

Regarding the cooling, you are burning less fuel at lower RPM and getting more mechanical work per volume of gas burned, so you need less cooling.

At 800 RPM you might be lugging the engine. At 1500 RPM, I don't see how that qualifies with an engine capable of variable timing.

I think you're points are mainly academic. In truth, at idle (700rpm) the Boxster 2.5 is producing only 27HP and 22 Ft.lbs., it's right there in the owners manual. And it doesn't get much better until you're waay north of 2500rpm. Not much to push a 3,000lb. car.

But, there's a practical experiment you can do. Start your car and try to idle (or up to 2500rpm) in 5th or 6th from a standing start. You'll soon learn how possible it is to 'lug' the engine, that is if it doesn't simply stall out first. Why? Because the load exceeds the power of the engine at that rpm level.

Yes the timing is variable, but only within limits, same with the fuel delivery. You're gonna get knock, ping, detonation. You will be putting a greater load on the engine than the power it can provide at that rpm level to overcome that load - you'll be operating outside it's powerband - in other words, lugging it!

[CaptainObvious]

Nobody is suggesting that it is wise to drive at idle in a high gear. Plenty of people seem to think 2k to 3k is, and that's simply false.

[vath2001]

If I had to keep my car above 2800rpm most of the time, I would never use 4th or 5th with my Tip. I understand to not lug the engine down, but rolling down the road at 2200-2800rpm is not going to destroy an engine. If I need the extra boost, I drop down a gear or two to pass or climb a hill and run the revs into the 4000-5000 range. But once I'm done, I drop back to crusing range.

Is this wrong?