Hi Jay Quinn!!
On Tue, 24 Jun 1997, Jay Quinn wrote:
> OK, this is assuming that you don't have the no
> lead head on this car and thats why you need to add
> a lead substitute?
Lead acts as a barrier that prevents the metal of the valve seat
micro-welding itself to the metal of the seat in the head. If it does
micro-weld together, when the valve opens, minute amounts of metal are
torn from the weakest component, which is the seat in the head. The
next time that the valve opens, the hot exhaust gases melt/burn the
contaminating metal particles from the valve face, and the whole process
begins again. This is called valve seat recession, as the valve seat is
gradually eaten away, and the valve slowly sinks into the head.
The reason why the process is engine load dependant, is because it keys
on the temperature of the exhaust valve. The heavier the engine
loading, the hotter the exhaust valves get. App. 80 to 90% of the valve
cooling is done through the seat in the head, with the other 10 to 20%
through the valve stem. If you end up with a gap between the valve
face, and the head seat, the valve overheats and burns.
You're zipping down the highway at 50 mph, with a slight
tailwind, and a slight downgrade... no problem. But, you're
pounding along at 75, with a 20 mph headwind, on a slight
upgrade, in third over, or forth under, using the throttle to set your
line as you drift through the corners... them thar valves are jest
aglowin a nice orangy-white.
> Otherwise, why? And what would the avdantage be?
I'm told that it's much more productive to make low octane "gas"
than it is to make high octane, so the refineries used to "crack"
low octane gas from crude oil, and raise its' octane rating with the
cheapest chemical octane enhancer available... tetra-ethyl lead.
They needed a lot more lead to raise the octane number than they did to
prevent valve recession.
TTUL8r, Kirk Cowen (who wasn't allowed to work on aircraft exhaust
systems if he had any cuts, or open sores on his hands)
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