REFLECTOR:Timing Change for Lycoming IO 360 C Engines?

[Jim Sower]

I'm pretty sure the 25 deg timing on Lycs has a lot more to do with 1920s technology
and the fact that mags can't be advanced and torsionals at idle with 25 deg advance
and etc. than with detonation.  If we were to look at the various EI systems, we
discover that idle timing is pretty close to zero (significantly reducing torsional
vibration and attendant crankshaft loads) and somewhere between 35 and 40 at cruise
power and rpm.  Has there been a bunch of crankshaft AD's on IO-360s, or was it all
the 540s?  I don't know how serious the torsional loads are idling way out of time,
but that's my first guess.  Detonation would have to be waaay down my list considering
the performance of EI.

But then again, what can we reasonably expect from an outfit that sets us up to where
we're 15* - 20* too far advanced at idle, 10* - 15* too far retarded at cruise, and
those are pretty much the only regimes that get used.  All hail Lycoming and their
wondrous technology!!
I guess I just don't properly appreciate the pioneers of 80 years ago .... Jim S.

Brian Michalk wrote:

> What's the compression ratio of this engine compared to the other IO360
> variants?  It could be because it is higher in this particular engine.
> Also, is the cylinder dome (squish volume) geometry different in this engine
> than the oer flavors?
>
> My guess is that they are having detonation problems.
>
> The downside is that retarding the timing will also decrease the horsepower
> or efficiency.  Pick one, not both.
>
> I would sure like to see the horsepower curves with these two timing
> changes.  Too bad the ignition is not electronic.  Retard for high manifold
> pressures, then advance for part throttle cruise ops.
>
>  Brian Michalk  <http://www.michalk.com>
> Life is what you make of it ... never wish you had done something.
> Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
> musician, home-brewer, entrepreneur and barely single
>
> > -----Original Message-----
> > From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
> > Behalf Of Ronnie Brown
> > Sent: Thursday, April 22, 2004 6:14 AM
> > To: reflector@tvbf.org
> > Subject: REFLECTOR:Timing Change for Lycoming IO 360 C Engines?
> >
> >
> > A discussion on the RV list says that Lycoming issued S.B. 380A "IO-360-C
> > Timing Change"  - requiring a change from 25 degrees to 20 degrees BTDC.
> > Any body got the contents of this bulletin or know what the reasoning is?
> >
> > THANKS
> > Ronnie Brown
> >
> >
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--
Jim Sower ... Destiny's Plaything
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T