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I'm sure there
is someone
out there that has accurate data - and you know who you
are!
Gary Casey
IO-540, 2 mags, but one might get exchanged for
something else.
You rang ???
Regards,
George
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OK...
seriously, the problem with answering that question - - which we
could do - - is that it leads to a lot of wrong assumptions about what is
"good". Other technologies would lead a lot of people to do some very
wrong things with their ignition systems.
Properly timed,
an IO-540 operating at WOT at high power (25 to 28"MP) can have a BFSC down
around 0.39 to 395. (with 8.7:1 pistons). At lower MP (20")
the BSFC will not be as good.
A 520/550 class TCM engine will do about
0385 under the same scenario.
These are very good numbers that the
automotive world does not achieve.
Regards,
George
*******************
*******************
George, you are
right .385/.395 BSFC is VERY good and numbers the auto industry does not
match. A low friction 4 valve per cylinder auto engine will do well
getting a .43 BSFC at LBT (lean best torque). I never tested lean of
best torque. Obviously, BSFC goes up as you close the throttle due to
pumping losses.
However.....it does matter where the spark comes from. If the
mag or other device does not have enough spark energy to create a "Quality flame
kernel" then the burn duration will increase and the brake torque will
decrease. If it misfires, I believe we all can picture that problem.
Spark plug life can also be a function of available spark energy. Having
multiple coils may not be as important on aircraft engines (6 cylinders running
2700 RPM) as it is on auto engines (8 cylinders running at 6000 RPM) since
the time to saturate the coil is much longer for an aircraft engine.
But keep in mind turbocharged and high compression ratio engines require
more spark energy to fire the plugs. The other huge benefit to
electronic ignition is....the engine can crank with the ignition firing at TDC,
greatly making life easier on the starter. In defense of magnetos, I have
run an 8 cylinder engine with 14 to 1 compression ration to 10,000 RPM on a
single mag. However, a battery ignition made more power. Electronic
battery ignition is the best concept however, I think the question has to
be........Do you believe in the quality of the hardware???? Not what
system has the highest potential. I personally do not have any durability
experience with any of the aircraft electronic ignitions. Additionally, if you
are running a 7.5 to 1 C.R. non turbo 4 cylinder engine, then mags are probably
just fine.
Craig
Berland
IV-P
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