rs55611 (10/22/82)
As the experience of burning an exhaust valve illustrates (from an earlier news item), the main purpose of lead in gas is to provide some lubrication for valves. I don't clao (oops) claim to know too much about this, but I believe that the valves used in cars running unleaded gas are built somewhat differently. As to an appropriate mixture, I've heard that a good mix is 1/3 leaded regular with 2/3 unleaded premium. The good thing about this mixture is that 92 octane unleaded prem. and 89 oct. leaded reg. combine to give better than 92 octane total! This surprizing result is due to the fact that lead in gas allows a higher effective octane rating with a given amount of the octane additive. Supposedly, only a little lead is needed, but my approach would be to try to use as much leaded regular as you can in the mix without getting knocking, as excess octane doesn't buy you anything. I've been using such a mix for about a year with no problems. Bob Schleicher Bell Labs IX 1A-269
donch@sri-unix (10/25/82)
The question of leaded/unleaded gas as a determining factor in valve life
is dear to my heart (unanswered, but dear). All of my vehicles, cars and
motorcycles were designed with leaded gas as a given. I watched with
great concern during the early-mid 70's when engineering trade journals
came out with numerous articles about upgrading valve materials to
confront the change from leaded gas to unleaded. What seemed to be the
most prevalent comment was that valve life is normally enhanced by tetraethyl
lead in gas owing to a "cushioning" effect between the valve and the seat.
The main change in valve/seat materials was to harden them to take the extra
pounding without the lead cushion.
Now let's put that thought aside and I'll add to the confusion with
conflicting input. I recently had the privilege of meeting an Australian
gentleman named Phil Irving. He was deeply involved as a mechanical
engineer and designer with the British motorcycle industry starting in
the l930's. He worked as a designer for Velocette and was also largely
responsible for the legendary post-war Vincent. When asked about this
very topic of valve life and leaded gas he said "When they started putting
lead in gas back in the old days, what did they get---valve problems!
Now they take the lead out and what do they get---valve problems! I
don't get it!" Not an informative answer, perhaps, but at least the
confusion isn't limited to us.
Don Chitwood
Tek Labs, Tektronix, Inc.