driving below 2800 RPM = trouble?

[Brucelee]

Have you actually talked to an auto engineer who told you this? Different parts wear for different reasons, load is the leader in wear, not speed. Any mechanical engineer will tell you that.


Are you suggesting that load is lower at higher speeds?? How can that happen in normal aggressive driving?

[CaptainObvious]

Is the concept of "lugging" an engine even relevant with fuel injection? I mean in the good ole days, you could feed the car too much fuel. Now, the car will only feed what it knows it can burn.

What exactly is stressed more at low RPM? The engine has less torque.

Is driving a BMW 135i at 1500 RPM lugging the engine... when it is near the peak torque there?

[turbo23dog]

Let me offer a few scenarios as to what I believe it means to lug the engine.

Lets say you floor the car off the line in first gear. The engine will move the car forward in a happy manner. Now floor the car off the line in 4th, 5h, or even 6th gear. The engine will not sound happy and in my mind is akin to lugging the engine.

Here's another scenario: have the car in 6th gear as you brake for red light. Don't press the clutch in, just use the brakes... the engine will not be happy at anything less than about 15 mpg heading toward zero... that's lugging the engine. This also gets back to flooring the car in 6th without shifting to a lower gear to accelerate should the light turn green... that's lugging the engine.

So I believe that in the context of the above, as a happy medium between lugging the engine and driving it like you stole it, avoid mashing the gas pedal in a higher gear when under 3K rpms to keep the engine happy. Use a gear appropriate for the speed you are going, as well as how much you are accelerating.

[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.

[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.

[dennis]

I drive a manual by sound more than watching the RPMs....if it feels the engine is ready, I shift. If I'm getting on it, I wind out the gears more, if I am driving casually I shift through the gears quicker and soem times around 2k, if downshifting around a turn, sometimes at 1700