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

[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.

[victoreric]

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.

[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

[z12358]

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.
Z.

[djomlas]

yea,..not every car likes to be in high rpms but wow do these cars like it

[Paul]

It's not mine, but here's a happy Porsche:



In Germany they are driven this way for hours with no ill effects!

[djomlas]

thats awesome i hate when people drive their cars like old grandmas. heck u live once, mite as well enjoy it while ure down here

[Back2DTM]

i just redline a couple times a day to keep the engine clean