Todd Mullins wrote:
> > Electronic Iginition also supplies more
> > power to plugs than points,
>
> Disagreed. Electronic Ignition doesn't send a damned thing to the spark
> plugs. Electronic Ignition ONLY tells the coil when to fire.
Ah, but remember how a coil works.
The coil is inductive. This means any change in current flowing
through it will be met with an induced voltage that will try to
keep the current going through it stable.
If you put 12V across it and get a current flowing, then lower
the voltage to zero, it will put a voltage on the high tension
plug.
The catch is, the faster you bring the voltage from 12 to zero,
the higher that voltage will be. The idealized system with
no resistance and no capacitance will produce an infinite voltage,
the real world is much less.
The electronic ignition can make a cleaner wave edge from
12V to zero. No mechanical system like points can keep up. What
happens is that the points together are a good conductor, the
points apart are a good insulator, but in the microseconds they
are seperating, there is partial contact from fuzz, ionized
air (spark) and so on. This means that the transition from
current flow to no current flow is not ideal.
It really can make a big difference.
> There isn't enough information here to debate. And I still contend that
> any increases in power due to "hotter spark" come directly from the
> coil.
Same thing. A "hot" coil uses different winding ratios to get
more spark. But same principles apply.
> And can anybody else tell me why engine modifications require a
> different needle?
The needle sets the fuel curve. It relates the amount of
air the engine is consuming with the fuel supplied.
The taper sets the ratio. On one needle, a point
a centimeter higher might have 40% more cross section,
where on another needle it might be 35%.
What different tapers can do is give you things like
more fuel at WOT, more fuel at 3/4 speed, and so on. When
the engine internals are changed, the curves must change
as well.
Actually, even simple things sometimes require new needles. I
know on my Midget, replacing the airbox with something that
flows better requires different needles.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
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