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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
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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.