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

[Dave Philipsen]

And I forgot to mention in my previous post, if you're getting 26 
statute mpg at 150 kts and 6.5 gph, Sid, that's great.  So far, the best 
I've been able to do is a bit over 20 mpg at just under 8 gph.  I'll 
have to see if my hydraulic MT prop has a sweet spot down around 2250 rpm!



Sid Knox wrote:
> 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
>
>
>
> _______________________________________________
>   

-- 
Dave Philipsen
Velocity STD-FG
N83DP