Myles -
Octane has been a gray area for some people (me included). Octane calculations
from the 'pre-no lead' era were different from subsequent formulas such as R+M/2
(if that's even a correct example). How Av gas octane is calculated is unknown
to me.
I read an article years ago in a collector car publication that stated "octane
is octane". The information for the article had been provided by a well known
petroleum company. For example: if you mixed 5 gal. of 93 octane un-leaded with
5 gal. of 104 octane leaded you ended up with 10 gals. of 98.5 octane. (That
sounds too simple!) The bonus was that while the lead concentration was
lessened, there was still far more lead than what was needed to protect the
valve seats in high performance 'muscle car' engines, and you gained the octane
advantage.
I've been running 112 leaded in my 11:1 (948) A-Series race engine this year. I
think I read in David Vizard's book on the subject that most A-series race
engines could get by with 106 octane or so (unless you're running very high
compressions, i.e., 13:1 and up). I bet my engine would work fine with even 103.
Which raises a question I've been wondering about all season: Can you actually
lose a degree of performance by using a fuel with "too much" octane?
Greg.
MHKitchen@aol.com on 11/10/99 10:46:48 PM
Please respond to MHKitchen@aol.com
To: vintage-race@autox.team.net
cc: (bcc: Gregory Schulz/MED/IT/ATLAS COPCO)
Subject: Race Gas vs. Av Gas??
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
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