driving below 2800 RPM = trouble?

[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?

[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]

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.

[dennis]

My only confusion when reading all these posts is that everyone praises the car for being both a daily driver and high performing vehcle and I agree with that but if the rpm level is so sensetive I think less people would praise it around town, unless they all have tips?