REFLECTOR: Fw: IO-550 Fuel Flow Issues and running LOP

[John Dibble]

Sid Knox wrote:

Sid,

Very interesting.  I have been thinking that 100 octane is overkill for my Franklin
engine, especailly with dual ignition which helps reduce detonation.  I just wasn't
sure how to go about determining how low an octane is acceptable.  My engine always
runs cool so it seems like a good candidate for lower octane.  What is the compression
of your engine?

>   And I burn mostly (GASP!!) auto fuel in
> a high-compression engine.  How can I get away with this?  By paying
> attention to what my engine tells me via the instrumentation.  Once at
> altitude I set about 2250 rpm, about 22 in Hg MAP, and set fuel flow to
> about 6.5 gph.  This figures to about 26 mpg (statute)... better than many
> autos.

What about for take-off?

>
> The auto fuel (NO ethanol!) keeps the cylinders and spark plugs clean.

What about the lead deposits for the valves?  How many hours have you been running
this way?

John

>  If I
> have to buy 100LL at a destination airport, I buy only enough to get me home
> (with a generous reserve), so in practice I will actually have anywhere from
> say 10 to 30 % 100LL.  Back when I could buy 93 octane auto fuel, I usually
> did not mess with 100LL but now the best available around here is 91 octane,
> so I feel better mixing a little 100LL to raise the average octane level.
> And these performance numbers hold, year-after-year, so it isn't a one-time
> fluke, but real-world results.
> As Stephen Stilles says   "I love my aeroplane 'cause she's got style".
>
> Sid Knox
> Oklahoma Tree Top Flyer
>
> Velocity  173 RG  N199RS
> Starduster  N666SK
> KR2         N24TC
> W7QJQ  2m ssb, EM25
>
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