George wrote:

"Now, please excuse me if I break the wind on this fuels discussion,
but how in the world are you going to keep auto gas from vapor locking
going from 12,000 to FL 250 on an August day?  It is not easy to that,
now, even with 100LL."

Excellent point, and my answer is "beats me."  I know of several stories
of airplanes heat soaking in Phoenix at 125F ramp temperatures, and
after the avionics finally cooled and started to work, the climb to
altitude and cruise were entertaining until the fuel cooled down.  And
this was with 100 LL.

I think the  reality of using auto fuel is that one must carefully
manage the risk: reduced power settings, lower altitudes, cooler
temperatures, or be prepared for some moments of quiet while the fuel
breaks wind on its way to the engine.  Remember, it is EXPERIMENTAL.

MUCH more important in my mind is the longer term trends with avgas.
Apparently the oil biz can not make a lead free 100 octane fuel, at
least at a price we are willing to pay.  Hence the recent EAA initiative
to breathe life into a 91-96 unleaded avgas proposal.  The refineries
can make this, and to aviation specifications.  It is usable in about
90% of the piston engine fleet.  And it can be used in high performance
liquid cooled engines.  But high performance air cooled engines,
particularly turbocharged engines, would be left high and dry, or have
to operate with major de-rate of manifold pressure and lower red line
cylinder head temperatures, I would think.  The engine manufacturers are
probably praying for a FADEC breakthrough to control detonation.  I
wouldn't hold my breath for such a breakthrough to occur.  But George
seems to be on the right track with his research.

If you have a 5-10 year horizon, it seems to me that high performance
air cooled aircraft engines as we know them are an endangered species.

So, looking at the big picture, I think the issue is not use of auto
fuel (which has its own risks) but what happens if (when?) supplies of
100LL start to disappear or skyrocket in price.  To me, a world of lower
octane fuels means a requirement for much lower cylinder head
temperatures (20F decrease in CHT is roughly equal to 1 octane number
reduction) which means liquid cooled engines.

Continental Voyager engines like that in the Extra 400 may be in your
future.  Maybe Continental will sell  you some liquid cooled jugs for
your TSIO-550.  And Lancair will come out with a belly scoop option with
radiator.  Think about it.  Personally I  prefer an engine designed from
the ground up to be liquid cooled.  But that is my prejudice surfacing
yet again.

Let the controversy continue!!

Fred Moreno