driving below 2800 RPM = trouble? - Page 2 - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Perfectlap · 04-04-2009, 03:34 PM

I think there's a happy medium...don't stay below 3k and maybe don't keep it up too high either. I'm guessing if your Boxer engine stays between 3-5K RPM 90% of the time and you go no longer than six months or 7.5K miles on the same oil you should have a long lasting engine. and of course keeping the RPMs no higher than 3k before the oil temp is up too

p.s.
Advanced Auto Parts has a special sale on Castrol Syntec, 5 quarts and a K&N oil filter for $25. Pep Boys sells it for $7 each. I plan to buy four of these lots, go with Honda Civic filters and sell the four of them for $15 or whatever. They sell for $13 each without the sale. That ought cover the two Mahle Boxster filters I picked up for $20. I'm going to go with 5w40. Hasta la vista Mobil1 and short shifting.

pbanders · 04-04-2009, 07:43 PM

FWIW, I feel sorry for any owner who is so concerned about IMS failure that they feel they have to drive at over 3K all the time. If you really believe the motor is that poorly engineered, either spend a wad of cash to get Jake to fix it for you or get rid of it.

I drive the cars I own for my pleasure, if they can't take the way I want to drive them, then I'll get something else.

Lordblood · 04-04-2009, 10:05 PM

This is worrying, the two people that mostly drive my Box keeps the RPM's between 2-3k almost 90% of the time. I think my sister also lugs the engine a lot, keeping in higher gears when slowing down then booting the throttle.

I always thought it being ricey to always keep the RPM's blisteringly high, but if the cops catch me for making too much noise, I can always tell him I'm saving my car from destruction :P.

cvhs18472 · 04-05-2009, 04:25 AM

Quote:

Originally Posted by pbanders

FWIW, I feel sorry for any owner who is so concerned about IMS failure that they feel they have to drive at over 3K all the time. If you really believe the motor is that poorly engineered, either spend a wad of cash to get Jake to fix it for you or get rid of it.

I drive the cars I own for my pleasure, if they can't take the way I want to drive them, then I'll get something else.

Here, Here.
Ed

kls · 04-05-2009, 07:26 AM

I think Perfectlap's suggestion for driving is ideal. No sacrifice at all, and no guilt for pushing it a bit. I do not see it as being overworried about IMS - just doing what you can to avoid an unlikley issue (like taking an aspirin every day for my healthy heart).

I have read on the LNE Engineering site that 5-40 oil is best, but it wasn't clear (at least to me) if that helped even if the seal to the IMS bearing had not been removed. I am going to increase the frequency of oil changes to 5,000 and use Castrol or RP.

I may be one of the people Pbanders feels sorry for, but I drive at the RPM I want, and use some common sense too.

spyder803 · 04-05-2009, 08:01 AM

The last thing I want is to mess my car up but I really can't imagine me ever lugging the engine, it runs too good to shift that soon. I'm going to just drive it the way I am comfortable driving it and let what ever happens happen.

LoveBunny · 04-05-2009, 03:27 PM

Quote:

Most IMS failures come in stop and go street driving, or in cars driven by Women.

This part makes me laugh because all of the men who have driven my car shift waaaay lower than I do, even my dad. I love the sound of the engine rev. I do a lot of stop-and-go city driving though so that sort of sucks.

Brucelee · 04-05-2009, 06:25 PM

Lets try this.

Yes, one should avoid lugging the engine. There is no exact RPM rule for this, as in first gear, you should not be able to LUG the engine, and in 6th gear, it is quite easy.

Second. The engine should be able to run safely between just above lugging and to just about red line. So, any exact RPM rule is clearly not appropriate for the issue of grenading the engine. The engine SHOULD NOT grenade.

Re: The IMS, Porsche should just fix the issue if it has not already.

Regarding wear: Higher RPMS cause greater wear than lower RPMs. Any auto engineer will tell you that, assuming you are NOT lugging the engine.

The whole drive it like you stole it advice is purely infantile, if you are talking about engine wear.

Having said that, if you want to trash your engine, be my guest. Just go to the track and beat it until it dies.

blue2000s · 04-05-2009, 06:32 PM

Quote:

Originally Posted by Brucelee

Regarding wear: Higher RPMS cause greater wear than lower RPMs. Any auto engineer will tell you that, assuming you are NOT lugging the engine.

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.

Brucelee · 04-05-2009, 06:40 PM

Both lead to wear on the engine. As I said, if you are not lugging the engine, you are not loading it unduly with low RPMs. If you are flooring the accelerator all the time, you ARE loading the engine unduly. Would you want to take you car to the drag races every day? Would it comfort you to know that you are not lugging the engine?

If you are running at 6000 RPMS all the time, you are elevating friction, heat. and wear. Pistons have to reciprocate. When you move them at 6000 rpms rather than 3000 RPMs, and they have to reverse direction, at which RPM do you think there is more stress on the cranshaft and the pistons?

Think about it.

blue2000s · 04-06-2009, 05:57 AM

Quote:

Originally Posted by Brucelee

Both lead to wear on the engine. As I said, if you are not lugging the engine, you are not loading it unduly with low RPMs. If you are flooring the accelerator all the time, you ARE loading the engine unduly. Would you want to take you car to the drag races every day? Would it comfort you to know that you are not lugging the engine?

If you are running at 6000 RPMS all the time, you are elevating friction, heat. and wear. Pistons have to reciprocate. When you move them at 6000 rpms rather than 3000 RPMs, and they have to reverse direction, at which RPM do you think there is more stress on the cranshaft and the pistons?

Think about it.

Ah Bruce, we've had this discussion before, I've shown you data, and you still ask the same questions. There's nothing else I can do for you.

Brucelee · 04-06-2009, 06:15 AM

Quote:

Originally Posted by blue2000s

Ah Bruce, we've had this discussion before, I've shown you data, and you still ask the same questions. There's nothing else I can do for you.

Repost the data. I don't recall. Again, explain please how load, friction, heat, are all lower at higher rpms. Explain why running your engine at near redline reduces wear than say at 3000 rpms. Are you suggesting that if I drive 90 MPH that the load on the engine is lower than if I drive at 65? If my MPG is lower at the higher speed, does that not reflect the extra energy consumed by the engine to push the air away to attain that speed? Does the extra load lead to extra wear?

If the laws of physics have been changed, I would like to know.

BTW-I too have posted information from engineers on this topic before.

Brucelee · 04-06-2009, 06:17 AM

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 · 04-06-2009, 09:53 AM

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 · 04-06-2009, 11:40 AM

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 · 04-06-2009, 12:39 PM

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 · 04-06-2009, 04:27 PM

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 · 04-06-2009, 04:52 PM

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 · 04-06-2009, 05:33 PM

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

Jaxonalden · 04-06-2009, 06:55 PM

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.