Hi, Lee,
You're right about 100LL fuel. 100-octane aviation gas certainly works quite
well in cars. As you mentioned, it's got lots of lead. Even though it's called
"low lead," it actually contains about twice as much lead as auto gas did
BEFORE the lead reduction took place (late 1980s?), and some people with auto
engines in their aircraft have reported problems with lead-fouled plugs and,
ironically, even sticking valves, which the lead is put there to prevent (and
it seems to do so in aircraft engines quite nicely). A hotter plug would
probably solve the plug fouling problem, and the reported valve sticking
problem is somewhat controversial (maybe in low-speed or low-power
operation?). The main drawbacks (other than its questionable legality) are its
cost and availability. Bring lots of cash if you plan to buy this stuff.
I've seen auto fuel aviation STCs for 80/87 octane automobile gas (unleaded),
to be used as-is in various aircraft, as long as there's NO ALCOHOL and the
Ried vapor pressure is not too high (aviation gas is generally less volatile
than auto gas).
There are a bunch of lead-substitute additives available for use with unleaded
auto gas, so burned valve seats are not really a problem. This valve seat
problem can also be fixed by installing hardened exhaust valve seats when
rebuilding the engine. The real problem is with alcohol in older fuel systems.
There are alcohol test kits available from several sources...usually about 10
to 15 dollars and good for lots of tests. It seems that Sporty's Pilot Shop
has them. Maybe Aircraft Spruce and Specialty Company would carry them. I plan
on using one this winter.
Of course, if you're on a road trip, you don't often have much choice as to
where you buy gas, unless you've got a reserve tank, so I suppose the ultimate
solution is to upgrade the fuel system to handle alcohol. This could involve a
different fuel pump (if you can't find an overhaul kit with newer soft parts),
different rubber fuel lines, a newer carb kit with additive-resistant parts,
etc.
If anyone knows how to purge alcohol from gasoline, I'd like to know how it's
done...and whether or not it's practical.
Alan
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