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I'm looking for opinions re. limited use of avgas in my Spider. The only reason is to do some tuning this winter, and I wonder if my usual source of race gas has fresh stuff, given the limited demand in a Michigan winter. I've removed the old gas from last summer.
 

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Richard Jemison
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Avgas

All you can buy is 100 octane low lead. (light blue color)

If 100 octane does it for you compression wise. (11 to one max if used in a race level environment)

I use in in the Montreal, tractors and farm equipment as it stores far better than automotive gas even alcohol free auto fuel.
 

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Push hard and live
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Note that Avgas has a TON of lead in it, even the 100LL "low lead". Plus, it is formulated to have a fairly low vapor pressure, as it is assumed it will be operating at high altitudes where a high vapor pressure fuel could have trouble with vapor lock, among other things.

Auto gas is reformulated between winter and summer, modifying the vapor pressure to help with the assumed ambient temperatures. It is always cold up high, so Avgas doesn't approach its formulation that way. It's a little like having winter gas even in the summer. Might be hard to start, among other things.
 

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Thanks.......I would be reluctant to just go with 100 octane, Ihave12:1compression.
Avgas octane rating is different than road fuels and even has different ratings for aviation "lean" and "rich" applications (see this Wikipedia page).
 
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