driving below 2800 RPM = trouble?

[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?

[BoxsterLewis]

Heres a question: Which way uses more gas, keeping it below 2800 or above. It seems like youd have to press the pedal more when you are in a lower range to get it moving than when you have the RPMs high but it also seems youd waste more gas keeping em high?

[Perfectlap]

You get great gas mileage keeping the revs low and driving smoothly (no herky jerky braking or throttle). I just spent the whole weekend driving it like uhh a Porsche. I'd say my gas mileage took a good 35% hit, at least. Keeping it above 3K requires a great deal more downshifting than I realized. Need to brush up on my heel and toe shifting! LOL

[Brucelee]

Einstein used to like to do thought experiments. Lets do one with this.

Driver A sets out for cross counrtry trip, 3500 miles on the Interstates. To make this fun, he simply gets in, drives at 75 MPH and about 3000 RPMs.

Now, Driver B is sure that this low RPM crap is for the birds. He knows his car should be meant to be driven faster, at higher RPMs.. Anything less that 6500 RPMs will ruin his race intended Boxster, even though it is a stock Box. Hey, Porsche is a racing company right?

So, off he goes. Now, in this experment, there are NO speed limits, so he can run at 6500 RPM the whole way. He can use any gear he wants, so he choose to cruise in sixth grear, which maybe nets him about 140 MPH????

Anyway, off they go.

Now, who gets there first? Well, if both engines hold up, clearly driver B if he choose to go faster than 75 MPH.

Now, whose motor was STRESSED more? which car's oil ran hotter during the entire trip? Which motor would have worn more, even if we can't measure it right now? Which oil is still fresh as a daisy after 3500 miles.

What do you think?

[Paul]

Porsches are made to be driven at 6500 rpms all day long. And they do so in Germany everyday of the year.

The car will last longer than most of us have left, so enjoy it.

[Brucelee]

Originally Posted by Paul

Porsches are made to be driven at 6500 rpms all day long. And they do so in Germany everyday of the year.

The car will last longer than most of us have left, so enjoy it.

Actually I never said they woudn't. The assertion made here is that they will NOT drive all day long at say 3000 RPMs and that the 6500 level results in less engine wear and risk of IMS implosion.

[Brucelee]

Originally Posted by 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?

Nope. This is the way to better gas mileage and reduced wear on your car.

[Lil bastard]

Well, just to add a little more fact to the mix, here is what Porsche says about engine operation and gear shift points from the '99 owners manual:

"The specified maximum rpm figures should not be exceeded when shifting down, exceeding the safe operating limit can result in damamge to the engine.

For smooth shifting, observe observe the following shift points (applies to standard gear ratios only):

Maximum downshifting points

• 5th to 4th ... 120mph/193km/h or 5100rpm
  4th to 3rd ... 84mph/135 km/h or 4700rpm
  3rd to 2nd ... 56mph/90 km/h or 4400rpm
  2nd to 1st ... 35mph/56 km/h or 4000rpm

Minimum upshifting points

• 1st to 2nd ... 15mph/24 km/h or 3000rpm
  2nd to 3rd ... 25mph/40 km/h or 2900rpm
  3rd to 4th ... 40mph/64 km/h or 3100rpm
  4th to 5th ... 45mph/72km/h or 2500rpm"

Now it seems to me, by strictly observing this, you'll be in the 'disputed' range and not lugging the engine.

[Perfectlap]

Interesting...I don't think I've ever downshifted to 1st from 2nd.

[Brucelee]

Originally Posted by Lil bastard

Well, just to add a little more fact to the mix, here is what Porsche says about engine operation and gear shift points from the '99 owners manual:

"The specified maximum rpm figures should not be exceeded when shifting down, exceeding the safe operating limit can result in damamge to the engine.

For smooth shifting, observe observe the following shift points (applies to standard gear ratios only):

Maximum downshifting points

• 5th to 4th ... 120mph/193km/h or 5100rpm
  4th to 3rd ... 84mph/135 km/h or 4700rpm
  3rd to 2nd ... 56mph/90 km/h or 4400rpm
  2nd to 1st ... 35mph/56 km/h or 4000rpm

Minimum upshifting points

• 1st to 2nd ... 15mph/24 km/h or 3000rpm
  2nd to 3rd ... 25mph/40 km/h or 2900rpm
  3rd to 4th ... 40mph/64 km/h or 3100rpm
  4th to 5th ... 45mph/72km/h or 2500rpm"

Now it seems to me, by strictly observing this, you'll be in the 'disputed' range and not lugging the engine.

Good stuff. thanks.\

[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.

[pbanders]

Originally Posted by Perfectlap

You get great gas mileage keeping the revs low and driving smoothly (no herky jerky braking or throttle). I just spent the whole weekend driving it like uhh a Porsche. I'd say my gas mileage took a good 35% hit, at least. Keeping it above 3K requires a great deal more downshifting than I realized. Need to brush up on my heel and toe shifting! LOL

This is why I quit commuting in my Boxster (that's what I use the Fit for). I found myself starting to thinking about gas mileage, tire wear, brake wear, etc. That's the last stuff I want to worry about when I drive my Boxster.

If reasonable but spirited driving helps keep my IMS healthy, all the better. If it doesn't, and my IMS blows anyway, despite regular maintenance, then I'll deal with it then.

BTW, the great part about my Fit is that I can drive it flat-out on my commute and nobody around me can tell! And it still gets over 30 mpg when I'm thrashing it.

[Perfectlap]

^ Yeah I rented a Prius once. Drove from Orlando to Miami never going slower than 90 mph. I was passing Corvettes and Mustangs who were saving gas in the middle lane...oh the irony. When I arrived at my destination I managed 30+mpg.

agreed, saving less than a grand a year on gas by short shifting and keeping the revs low really looks silly in light of possibly causing a $8,000 emergency engine transplant.

[Paul]

IMO Porsches are toys, enjoy them or get rid of them. Many days the best part of my day is the 30 minute commute in each direction. That's why I drive at least one of my Porsches year round. This year it was the 3.6, what a blast when I floor it.

I must admit, however that since this is the most powerful Porsche I've owned, I cannot floor it from a dead stop unless I use second gear from a stop, since the acceleration in first is not manageable even with traction control, 265x18 tires and a LSD.

I'm currently looking for a 3.8 X51 for my 01 2.7.......

[Perfectlap]

^You can do that with an 00-02? I thought the electronics made it tough?

Man if me engine ever went, I'd certainly consider that. 381HP? Eat those Carreras for lunch.

EDIT:
"Hans Hoffman, Ruf’s technical guru in Dallas, advises anyone with a pre-2005 Boxster contemplating a 3.8S conversion that the main wiring buss for the ECU is completely different, and they are better off trading up to a later model Boxster"

[Paul]

If it can be done on a 98, it can be done even easier on a 01 since it already has Can bus and eGas. My 98 is running a 7.8 motronic.