[Fot] 110 Octane

Sat Feb 20 19:05:42 MST 2016

I guess we autocrossers that shop the local speed shops for a 5 gallon pail of Sunoco 112 race fuel and pay $65 ( !! ) we are easy victims for the corporate CEO's.

Gotta love the Kick thou

Cheers,
Bob T
'64 Spit GT  autocrosser

-----Original Message-----
From: Duncan Charlton <duncan.charlton54 at gmail.com>
To: 'Friends of Triumph' Triumph <fot at autox.team.net>
Sent: Sat, Feb 20, 2016 9:38 am
Subject: Re: [Fot] 110 Octane

I found an interesting chart of race fuel specs, and it includes AvGas (100LL only) for comparison.  http://smithtex.com/racing/fuelcomp.html

Just to complicate things Avgas can be rated by “aviation lean” (one typically leans out the mixture at higher elevations, judging by watching the exhaust gas temperature) or “aviation rich” (considering supercharging, high temperature and high manifold pressure) standards.  So you might see a rating like 100/130 which means that if you run it richer the knock resistance is higher.   This fuel, I have read, has half the tetraethyl lead allowed in pre-1975 premium leaded auto fuel.

Octane numbers can confuse the unwary.  Most of you probably already know this, but it might be worth mentioning that the premium you buy at a street pump might be listed as 93 octane but that’s the average of Research Method (index of acceleration knock) and Motor Method (index of knock at high engine speeds), which is about the same as the stuff they call 98 octane in some other countries, which is classified by the Research Octane Number only.  Below the listed octane number on the pump one can often see the equation (RM + MM) / 2 or (R+M)/2.  The Research Octane Number is typically higher than the Motor Octane Number about 10 points but the chart I referred to suggests that it can vary by 4.9 to 14 points (“sensitivity”).  A “single grade” AvGas such as "110" is rated by the Research Octane Number, so 110 AvGas might be comparable to 96 octane race fuel or it might be more like 105 octane race fuel, depending on the brand of race fuel.

Whitfield Oil’s website mentions that Avgas has a lower specific gravity than most racing gasolines, which means it’s less dense, so the air/fuel mixture likely would need to be adjusted.

Among other differences, Avgas is formulated with lower vapor pressure, so there is less likelihood of vapor lock, particularly at higher elevations.  I’ve heard claims that motors run cooler on AvGas, so assuming it’s properly jetted, doesn't that mean it’s making less power?

Duncan
(Texas)

On Feb 19, 2016, at 9:36 PM, Mike Jackson <grandwazoo at earthlink.net> wrote:

It's a long story.  Short version, I run race fuel in the TR3 but AvGas in my FV motors.  I'm paying about $6/gal for AvGas.

Folks more knowledgeable than I am have explained that octane is not a "Gods Law" formula.  Consequently the formula for calculating octane for AvGas is very different from that for road going fuel.  So, 100 octane AvGas has no good way to compare to race fuel.  In general, aviation motors are lower compression than our race engines.  They need ultimate reliability since they cant coast to the side of the track if they throw a rod.

On the other hand, those same more knowledgeable folks told us in the FV community that AvGas "low lead" has more lead than road fuel ever did.  Same issue of reliability with valves and seats.

Mike

-----Original Message----- 
From: Bill Dentinger 
Sent: Feb 19, 2016 8:31 PM 
To: "J.C. Hassall" 
Cc: 'Friends of Triumph' Triumph 
Subject: Re: [Fot] 110 Octane 

Maybe he will chime in, but I know Mike Jackson, and others of his ilk, use to buy AV gas  at an airport and bring it to the track, where they would 'cut' it with regular pump gas.  Fifty/fifty, as I recall.  Seemed like a lot of extra work to me, but Mike said that AV gas must achieve a particular octane rating, which he trusted over and above what you might purchase at the track, or else where.

Bill Dentinger

Sent from my iPad

On Feb 19, 2016, at 3:38 PM, J.C. Hassall <jhassall at gmail.com> wrote:

Try your local GA airport. Here in Blacksburg VA 110 LL is $4.44 a gallon. 

jim

Fat-thumbed from my iPhone

On Feb 19, 2016, at 3:29 PM, Spitfire Racing <Spitfire_Racing at twcny.rr.com> wrote:

At Summit Point it’s also $8.85 @ gallon currently.

russ

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