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Old 11-04-2006, 06:05 PM   #1
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Keep her above 4000rpm and she'll thank you for it every day.

I had read an article a couple of years ago in Panorama which was a reprint from the late 1970s that was about a man who bought a used Porsche 911 and the previous owner told him "whatever you do, keep her above 4000".

Before this, when I purchased my 928 it was making all of this clacking noise that was driving me nuts. I posted it on the 928 forums and one reply was "take her down the highway, warm her up and run the piss out of her, then keep her above 4000 when driving". He further explained that carbon builds and clogs things up if you drive it like other cars. Once that happens, you have to run it really hard to clean it out. Keeping her above 4000rpm while driving around town keeps the carbon from building up and helps the engine run better.

After several people agreed with his comments, I made this a habit and the only time that noise comes back is when the wife drives her (keeps it in the 2-3Krpm range) or when it's about 500 miles to the next oil change.

The reason I wanted to bring this up is there's a lot of scepticism out there about what some say is "running the engine so hard". I've had some say "I could never do that to my baby" and similar comments. Others are concerned with lower mileage. Well, I finally got confirmation from the Porsche factory folks on my last mountain run so I thought I would share.

We have mountain runs occasionally with Porsches, Ferraris, BMWs & even a guy in a Pantera that are a blast. Last time there was a guy in a Cayman S who is a Porsche engineer. He had the car from the factory to drive it in every day situations to see how it performs (quite nicely I might add). As the day went on, we stopped several times and would just chat for a few minutes to break the stress of driving so hard through the mountains. At one of the stops I had the pleasure of talking to him and asked what he does for Porsche. As it turned out, he is an engineer who helps to figure out the causes of problems in engines. He tears them down after a failure or if there is a persistent problem and examines everything about it.

After learning about what he does for Porsche, I asked what the most common problem is. His answer was "I go to court for Porsche all the time when people sue us because the engine is running poorly, making lots of noise, sputtering, etc. We take the engine apart and there is carbon built up all over the place causing all of the trouble." I asked him what causes the build up and he said "Most of the buyers are older since a Porsche is an expensive car. The problem is they bought a race car and drive it like they would a Jaguar or Cadillac. They don't drive the car hard enough to burn off the carbon so the engine clogs up and it runs like crap."

This seemed to confirm the rule I had learned earlier so I asked straight up "So is the keep her above 4000rpm rule a good way to keep the engine clean?" He said "Yes, you should keep the engine in the 4000rpm range and above to prevent carbon problems over time. If you look at all Porsche tachometers, 4000rpm is straight up to make it an easy reference point." I checked when I got home and sure enough the Boxster's tach has 4000rpm straight up too even though the tach goes to 1000rpm higher than the 928's tach.

So keep her above 4000 and she'll thank you for it every day.
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Old 11-04-2006, 06:14 PM   #2
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Good deal...I make sure my tach needle sees at least 7,000+ rpm a couple of times every drive I take....once the engine is properly warmed up of course. I've not had one iota of trouble with the car period. People who buy Porsches for garage art and/or baby their cars are really missing out on some fun and the whole point of ownership.
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Old 11-04-2006, 06:16 PM   #3
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Interesting, I was just thinking to myself last night as I was driving home... My car is going to last forever.... because it never goes over 4k .
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Old 11-04-2006, 06:21 PM   #4
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I now have an excuse to drive at 100mph for my everyday driving,on the freeway of course.
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Old 11-04-2006, 06:30 PM   #5
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If he testifies this in court the rebuttal would be to pull out an owner's manual...me thinks.

I guess the implied reason would be there is incomplete combustion below 4,000 rpm. Or would it be another factor?
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Old 11-04-2006, 06:34 PM   #6
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Originally Posted by wild1poet2
If he testifies this in court the rebuttal would be to pull out an owner's manual...me thinks.

I guess the implied reason would be there is incomplete combustion below 4,000 rpm. Or would it be another factor?

The owners manual does NOT discourage driving above 4,000 RPM. Except during the 2,000 mile break-in period.
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Old 11-04-2006, 06:58 PM   #7
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Originally Posted by bmussatti
The owners manual does NOT discourage driving above 4,000 RPM. Except during the 2,000 mile break-in period.
Good point. I should have mentioned it's not a good idea to run her above 4000rpm if you're in the break-in period. My manual only says to stay under 4200rpm for the first 1000 miles. YMMV
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Old 11-04-2006, 07:00 PM   #8
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Originally Posted by deliriousga
Good point. I should have mentioned it's not a good idea to run her above 4000rpm if you're in the break-in period. My manual only says to stay under 4200rpm for the first 1000 miles.
Mine says the first 2000 miles
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Old 11-04-2006, 07:26 PM   #9
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Originally Posted by wild1poet2
If he testifies this in court the rebuttal would be to pull out an owner's manual...me thinks.

I guess the implied reason would be there is incomplete combustion below 4,000 rpm. Or would it be another factor?
Hi,

There are lots of other factors. An engine never achieves complete combustion, if that were true, we'd never need emissions gear.

But, there is an RPM range in each engine where the combustion is most complete, and from the sound of it, it's in the 4k range for the M96 engine.

But other factors contributing to long life, maybe even the dominant factors, are that the Crankspeed dependent Oil and Coolant pumps (run off the crank-driven serpentine belt) may be in their most efficient range here as well.

All the engineer was speaking about was Carbon build-up, but a steady supply of Oil and Coolant will mean more to longevity than the buildup of a little Carbon. Carbon is softer than steel or aluminum and actually acts as a lubricant and sealant. You need some, but too much is a problem because it causes hotspots (retains heat) in the valvetrain and interferes with heat transfer to the head where the coolant can carry it away.

And, you need to put this into perspective. Incomplete combustion takes places at either end of the Tach. At some place north of 4k rpm, the piston doesn't remain at the top of the Compression Stroke long enough to combust all the fuel, even with an altered timing curve. This is why you often hear an exhaust popping on deceleration from a hard run, because unburnt fuel has accumulated in the exhaust and ignites there instead of in the cylinder where it's supposed to.

The interesting thing to me is that Porsche doesn't gear the Tiptronic or the Control Unit to shift at 4k rpm, I wonder why they wouldn't do that? And, the Tip cars generally have a more trouble-free life than the Manuals...

Happy Motoring!... Jim'99
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Old 11-04-2006, 07:26 PM   #10
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Sure, I used to tell the cop that it was to blow out the carbon.

It was a lie then, a lie now!
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Old 11-05-2006, 05:45 AM   #11
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Once again I will calmly state that I have been shifting my Porsches at or near redline since the 70's and I have yet to have an engine problem.

Baby it, it will punish you.
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Old 11-05-2006, 10:22 AM   #12
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Originally Posted by Paul
Once again I will calmly state that I have been shifting my Porsches at or near redline since the 70's and I have yet to have an engine problem.

Baby it, it will punish you.
I am surprised you still have a license.

How does that work in your driveway and garage?
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Old 11-05-2006, 10:57 AM   #13
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Originally Posted by MNBoxster
Hi,

There are lots of other factors. An engine never achieves complete combustion, if that were true, we'd never need emissions gear.

But, there is an RPM range in each engine where the combustion is most complete, and from the sound of it, it's in the 4k range for the M96 engine.

But other factors contributing to long life, maybe even the dominant factors, are that the Crankspeed dependent Oil and Coolant pumps (run off the crank-driven serpentine belt) may be in their most efficient range here as well.

All the engineer was speaking about was Carbon build-up, but a steady supply of Oil and Coolant will mean more to longevity than the buildup of a little Carbon. Carbon is softer than steel or aluminum and actually acts as a lubricant and sealant. You need some, but too much is a problem because it causes hotspots (retains heat) in the valvetrain and interferes with heat transfer to the head where the coolant can carry it away.

And, you need to put this into perspective. Incomplete combustion takes places at either end of the Tach. At some place north of 4k rpm, the piston doesn't remain at the top of the Compression Stroke long enough to combust all the fuel, even with an altered timing curve. This is why you often hear an exhaust popping on deceleration from a hard run, because unburnt fuel has accumulated in the exhaust and ignites there instead of in the cylinder where it's supposed to.

The interesting thing to me is that Porsche doesn't gear the Tiptronic or the Control Unit to shift at 4k rpm, I wonder why they wouldn't do that? And, the Tip cars generally have a more trouble-free life than the Manuals...

Happy Motoring!... Jim'99

Carbon can also build up on the intake side. As fuel is exposed to a hot intake valve, it can solidify and build up. The build up within the ring seals is also partially irrespective of combustion. The faster engine speed gives the fuel less time to sit on hot surfaces as it is raced into the combustion chamber.

Also, don't forget about fuel quality and the presence of oil, which are also contributors.
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Old 11-05-2006, 11:26 AM   #14
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"The interesting thing to me is that Porsche doesn't gear the Tiptronic or the Control Unit to shift at 4k rpm, I wonder why they wouldn't do that? And, the Tip cars generally have a more trouble-free life than the Manuals"

That IS actually pretty interesting.

And BTW- if very high RPM were good for engine life, imagine how long a NASCAR engine should last! Driven JUST BELOW REDLINE for hours on end and with fresh Mobil 1 to boot!

Think of it, a million mile NASCAR engine!!!!!!!!!!!!!!!!!!!!
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Old 11-05-2006, 11:56 AM   #15
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Carbon can also build up on the intake side. As fuel is exposed to a hot intake valve, it can solidify and build up. The build up within the ring seals is also partially irrespective of combustion. The faster engine speed gives the fuel less time to sit on hot surfaces as it is raced into the combustion chamber.

Also, don't forget about fuel quality and the presence of oil, which are also contributors.
Hi,

Well, definitely too much Carbon buidup isn't good, but the fuel is meant to actually bathe the Intake Valves as part of the process of cooling them.

The only 2 ways a Valve can shed it's heat is to either transfer that heat to the fuel which flows past it, and/or for that fraction of a second in each cycle where the Valve is closed and actually in contact with the Valve Seat, thereby transferring it's heat to the Head where the Coolant carries it away.

Again, too much Carbon, especially on the Valve Seat, and you interfere with this heat transfer by essentially creating an insulating layer.

I also agree that the quality of the Fuel, and the general health of the engine (where Oil isn't leaking into the Comcustion Chamber) will play a large part in preventing excessive Carbon buildup...

Happy Motoring!... Jim'99
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Old 11-05-2006, 01:22 PM   #16
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Originally Posted by MNBoxster
Hi,

Well, definitely too much Carbon buidup isn't good, but the fuel is meant to actually bathe the Intake Valves as part of the process of cooling them.

The only 2 ways a Valve can shed it's heat is to either transfer that heat to the fuel which flows past it, and/or for that fraction of a second in each cycle where the Valve is closed and actually in contact with the Valve Seat, thereby transferring it's heat to the Head where the Coolant carries it away.

Again, too much Carbon, especially on the Valve Seat, and you interfere with this heat transfer by essentially creating an insulating layer.

I also agree that the quality of the Fuel, and the general health of the engine (where Oil isn't leaking into the Comcustion Chamber) will play a large part in preventing excessive Carbon buildup...

Happy Motoring!... Jim'99
The fuel is primarily sprayed onto the intake valve not to cool it, but to enhance the atomization of the fuel. It is a side benefit that the heat from the valve is carried away by the air/fuel. The valve is also cooled by the air/fuel rushing past it on the intake stroke. FSI engines show that the intake valve can opperate just fine without spraying fuel on them.

Typically, it's the exhaust valve that has the cooling problems as the hot gasses of combustion run past it and the valve's size is somewhat smaller than the intake. This is why you'll find sodium filling in exhaust valves and not on the intake side.

Last edited by blue2000s; 11-05-2006 at 01:25 PM.
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Old 11-05-2006, 01:31 PM   #17
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Cuts your gas mileage by about third though...I have been trying it lately.
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Old 11-05-2006, 06:45 PM   #18
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Very interesting & thanks for sharing that. Now I don't have to feel guilty about pushing mine to 5000. That's when the engine let's out that nice growl.
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Old 11-05-2006, 07:28 PM   #19
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Quote:
Originally Posted by blue2000s
The fuel is primarily sprayed onto the intake valve not to cool it, but to enhance the atomization of the fuel. It is a side benefit that the heat from the valve is carried away by the air/fuel. The valve is also cooled by the air/fuel rushing past it on the intake stroke. FSI engines show that the intake valve can opperate just fine without spraying fuel on them.

Typically, it's the exhaust valve that has the cooling problems as the hot gasses of combustion run past it and the valve's size is somewhat smaller than the intake. This is why you'll find sodium filling in exhaust valves and not on the intake side.

Hi,

I actually meant the AF mix, guess I oversimplified. I know the Boxster has Sodium-filled Exhaust Valves, so does my Esprit...

Happy Motoring!... Jim'99
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Old 11-06-2006, 05:09 AM   #20
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On the highway, the straights, and mostly when my fiance is with me I keep it between 3k-5k. On the twisties, and especially when riding solo, the 5k+ growl informs me about the area to shift. Few times during a run, I'll take it to 6.5k. On the track, the needle rarely goes below 4.5k. There's something about this car that makes high rpms so inviting and right.
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