MHKitchen@aol.com wrote:
>
> Since we're on the subject of gas.....
>
> I've had to use 110 octane leaded CAM2 or Sunoco race gas in the twin cam
> with its 13.5 :1 compression ratio. But it does get expensive!!
>
> I was convinced to try Aviation Gas this summer up in Seattle, which seemed
> to work fine...no detonation or performance issues. And it was 50% or less
> of the cost of race gas.
>
> Recently, I tried to buy more Av gas here in CA, but found a) that no one
> would sell it to me in a jug...would only dispense it into a plane, and b) I
> find that they now only sell "low lead" Av gas with an octane rating of 100.
>
> I've heard that the "low lead" Av gas @ 100 octane is REALLY equivalent to a
> higher octane automotive fuel, which I'd tend to believe since it worked so
> well.
>
> Does anyone out there have any definitive answers on using Av gas in race
> engines? I hear stories pro and con about it. I would tend to agree that Av
> gas comes under higher scrutiny and quality control than race gas..but is
> there a downside?
>
> Inquiring minds want to know???
>
> Myles H. Kitchen
> Air Cortina Pilot
> 1965 Lotus (about to rotate) Cortina Mk1 #128
Myles
During the 1973 gas crisis, I ran my R code 72 Mach I (351 Cleveland
10:1 solid liftered) on Avgas since I didn't have to wait in line for it
and was Director of Maintenance for a flying club. At that time it was
still 100 octane leaded. The 100LL octane was not out yet. The car ran
fine put abiout 20,000 miles on it. Only difference I noticed was that
it was a little more difficult to start in the winter due the difference
in vapor pressure characteristics between avgas and mogas. In 77-78 I
ran my 76 Mustang on 100LL at times and experienced no difficulties with
valves etc. However using the 100LL in aviation engines designed for 80
leaded was disasterous for the first couple of years. Shell guys were
telling us that it was fine and wouldn't do any harm.... from all their
test data in the lab. The facts were that in the real world engine that
had historically gone to 2000 to 2400 hours between overhauls were
losing valves at 300 to 500 hours. It turned out that the valves were
getting build ups on them and then not closing fully causing missing and
eventual failure of either the seat area or valve breakage due to
overheating the valve. It was eventually found that by special mixture
leaning procedures much of this could be eliminated. One of the driving
reasons behind the EAA getting STC certificates for using unleaded mogas
in aircraft was because of the failures being experienced using 100LL in
engines designed for 80 octane leaded.
My 70 Boss 302 with 11 to 1 theoretical (10.5 actual) compression ratio
will run on the street with no knock with about 25% 104 octane Turbo
Blue mixed with 93 octane unleaded. However when I take it on the track
for hi speed autocrossing or open track events it is running on 75%+ 110
octane leaded racing gas. When I took a vintage drivers school in it in
May, I went through $120 worth of 110 octane in 4 -1/2 hour sessions. I
still thought it was cheap insurance against destroying an engine that
will cost me over $6000 in parts to start rebuilding if it grenaded and
took out block, crank heads etc.
Bill Dalton, PE
Commercial Pilot #2185719 CFII, AGI, IGI
SCCA National Tech 218743
VSCDA Chief of Tech
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