Keep her above 4000rpm and she'll thank you for it every day.

[blinkwatt]

I now have an excuse to drive at 100mph for my everyday driving,on the freeway of course.

[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?

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.

[deliriousga]

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

[Adam]

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

[Brucelee]

Sure, I used to tell the cop that it was to blow out the carbon.

It was a lie then, a lie now!

[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.

[MNBoxster]

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

[blue2000s]

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.

[Brucelee]

"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!!!!!!!!!!!!!!!!!!!!

[MNBoxster]

Originally Posted by blue2000s

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

[blue2000s]

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.

[Rail26]

Cuts your gas mileage by about third though...I have been trying it lately.

[MNBoxster]

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

[mquillen]

Although carbon build-up isn't good, I suspect another reason (perhaps the primary reason) for the advice to keep the revs up was the fact that all of the early Porsches were air cooled. Keeping the revs up meant airflow--lugging an aircooled engine is the fastest way to kill it.

[MNBoxster]

Originally Posted by mquillen

Although carbon build-up isn't good, I suspect another reason (perhaps the primary reason) for the advice to keep the revs up was the fact that all of the early Porsches were air cooled. Keeping the revs up meant airflow--lugging an aircooled engine is the fastest way to kill it.

Hi,

You make an excellent point!...

Happy Motoring!... Jim'99

[70Sixter]

It was originally mostly a spark plug fouling issue. Before CD (in 69?) fouling was a major problem. Could happen in minutes, especially in traffic. Some people even put hotter plugs in for city driving and switched to cold ones for open road/track. We all tried to use Amoco Super Premium because it was the only lead free gas.

Low rpm carbon deposits can form around the top of the cylinder and the results can be disastrous after years of build-up when a trip to redline "stretches" the rod & piston into collision with the nasty carbon.

[blue2000s]

There are also mechanical (inertial) reasons to keep load down at low rpm. In general it's a good idea to keep in the higher rev ranges if load is going to be high. This is generally when you feel the need to "floor it".