content22207 wrote:
OK: you've got terms correct (don't take it personally -- many people
don't) but are incorrect on spark. Try it on your DeLo: time at 6-8
degrees and see what happens...
Bill Robertson
#5939
-----
You get cack all power. I've watched Darren tune up a car retarding the
ignition back to 6 degrees because it was knocking. I am not making this
up. Read www.pumaracing.co.uk and learn about how the spark actually
timed. Timing advance is the time before the piston reaches the top of
its stroke that the spark goes off. Too much advance and the fuel will
combust too quickly trying to push the piston back down before it
reaches the top. Retard the spark, ie reduce the advance and the spark
will go off when the piston is nearer the top of the stroke allowing
full combustion to occur after TDC. Bill. I'm right.
Buggerit - here's some text for you.
http://www.sdsefi.com/techcomb.htm
And now, Taken wholly from www.pumaracing.co.uk full credit to Dave Baker
Ignition Timing
It takes one or two milliseconds from the time the spark occurs until
all the fuel/air mixture in the cylinder is fully alight and expanding.
The spark plugs therefore need to be fired a little while before the
piston reaches Top Dead Centre so as to get the fuel mixture burning at
the right time to push the piston down and generate power. When measured
in crank degrees rather than seconds this time delay is called ignition
advance. The perfect time to trigger the spark depends again on engine
speed and throttle position. Cars used to use a mechanical distributor
to set the spark timing. Nowadays it is normally done by the ECU in a
similar way to how the fuel mixture is controlled. The ECU stores
another map on its chip of how much ignition advance is required which
operates just like the fueling map. Copyright David Baker and Puma Race
Engines
The amount of ignition advance required depends on the engine design.
Average figures would be between about 10 crank degrees at idle to about
30 degrees at peak rpm. The required advance usually increases with rpm
up to about 3,000 to 4,000 rpm and then stays fairly constant. It also
needs to increase at low throttle openings and reduce again at full
throttle. If the spark is fired too early (over advanced) then the
mixture starts to burn too soon and tries to push the piston backwards
down the way it came before it reaches TDC - very bad for power and a
major cause of engine damage. If the spark is fired too late (retarded)
the piston has already gone part of the way down the bore on the power
stroke before the mixture is alight and much of the effectiveness of the
energy released is lost.
If I had £1 for every person who thinks that more ignition advance is a
good thing in its own right I'd be a rich man. Like most other things,
more advance is only good if there isn't enough to start with. Excessive
advance is just as detrimental to power output as insufficient advance
but it's also potentially much more harmful to the engine. In fact the
better the engine design the less advance is required and other things
being equal, an engine that requires less advance will produce more
power. Copyright David Baker and Puma Race Engines
-------
Martin
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