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

[Sid Knox]

> My Performance Engines IO-550 seems to run very lean, both at idle and at 
> ground run-up.
> So lean, that if I shut down the Plasma ignition, it won't idle at all on 
> just the magneto.
> I also get no rpm rise on mixture cutoff, and it hesitates to come off 
> idle or low power.
> By accident, I once started it with low fuel pump boost on, and it ran 
> much better,
> even idling on the magneto side alone.
> Bill Walker

This could be more than an annoyance at idle... it would be destructive with 
take-off power!
Running lean-of-peak is a wonderful thing.  I run my IO-360C1C  LOP once 
established at cruise altitude or about 5000 feet or higher msl where the 
lower MAP reduces the peak combustion pressure and temperature.
To run too lean, full-power, at low altitudes is begging for detonation. 
With heavy detonation, cyl temps can hit 500F so quickly you may not even 
notice it before it is too late.
A word about LOP operation.  I have (DIY) balanced injectors,  fuel-flow, 
and of course cyl CHT and EGT instrumentation.  Being somewhat of a 
tight-wad, I am very much into economy flying.  I figure perhaps 30 minutes 
longer on a cross-country to save 20 ro 30 dollars in fuel is a good deal, 
so I am satisfied with 150 kt TAS.  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.  And this is real mpg based on TAS... not some bogus mpg based on IAS 
or ground speed.  The 3-blade MT (electric) prop has a sweet-spot around 
2250 to 2300 rpm so that is where I stay.  Further, the engine runs cooler 
and quieter at reduced power and I figure it will last longer than I will be 
around to fly it (yes, I'm an old guy).
The auto fuel (NO ethanol!) keeps the cylinders and spark plugs clean.  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