Hybrid Car – More Fun with Less Gas

better mileage with higher octane? - Page 11

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Posted by Eeyore on January 3, 2007, 11:39 pm

clare, at, snyder.on.ca wrote:

LOL. And sometimes it's *so* tempting to do just that.


Posted by clare at snyder.on.ca on January 3, 2007, 9:50 pm

On Tue, 2 Jan 2007 22:04:38 -0500, "Solar Flare"

Not true.
Higher octane fuel, generally, does NOT burn slower. In many cases it
can actually burn FASTER. High octane fuel simply resists
dis-associating the hydrogen radicals(H1, not H2) from the hydrocarbon
fuel under heat and pressure. It is the presence of these "free
radicals" which causes the fuel to detonate in the cyl.

To reduce detonation you either increase the Octane rating of the fuel
or reduce the amount of heat acting on the end gas. This is done by
reducing compression, retarding spark, increasing RPM, or engineering
the combustion chamber for a FASTER burn.

Lead did not have a "cooling effect". The lead COATING acted as both
an insulator and a lubricant on the valve seats, preventing the valve
from being "hammer welded" to the seat, pulling metal from the seat
and causing "seat errosion". This was a side benefit - TEL was added
to act as a "negative catalyst" to prevent the breakdown of the
end-gasses, reducing the production of the highly unstable hydrogen

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Posted by Solar Flare on January 4, 2007, 1:22 am

In order to use unleaded fuels car engines has to increase the
temperature handling of the valves and seats. Lead acted like a

<clare at snyder.on.ca> wrote in message

Posted by clare at snyder.on.ca on January 4, 2007, 2:01 am

On Wed, 3 Jan 2007 20:22:19 -0500, "Solar Flare"

No it did not. It was a lubricant and prevented the valve face from
"welding" to the seats. Seat recession was caused by pits being torn
out of the valve seats. Stelite or induction hardened seats resist
this action. It also took VERY LITTLE lead to have this effect. One
gallon of leaded fuel per 100 gallons is enough to protect the valves
of a "lead era" car. The result is also quite long lasting. A car that
has run leaded fuel can and will survive for many many hours without
valve damage on unleaded fuel.

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Posted by Solar Flare on January 4, 2007, 2:29 am

OK the valves and seats had to be hardened to stop the "sticking"
action of the valve due to less lubrication from the lead but not the
higher temperature. My bad.

However you stated that higher octane fuels do not burn slower and
then proceded to say they do again. Most articles will agree that
octane stops pinging by slowing down the detonation of the fuel under
heat and presure. This is not faster and the chemical reason doesn't
really matter, as it appears to support my statement and disagree with

When you disagree and then set out to re-enforce the other posters
statement it appears as an obsession.

<clare at snyder.on.ca> wrote in message

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