Vance wrote:
> - Cost: You are out the cost of the coil, and perhaps
> plug wires needed to handle the higher voltage.
So $25 for a stock style coil or $35 for a Lucas Sports Coil... not much of
a difference there. Even the Crane Coils I sell with Crane Ignitions are in
the in the $40 range... so cost is not too bad.
> The advantages lie in the following areas:
> - A hotter spark means that even the most heavily fouled
> plug will still fire. If you have a problem with plug fouling, then
> this can help. The real solution however is to fix the source of
> the fouling.
> - Emissions: a mis-firing plug can play havoc with your
> emissions and engine smoothness. A hotter coil means more
> margin to having a plug misfire.
All valid points. Even when your air fuel ratio is dead on, the mixture
that enters the combustion chamber is not a homogeneous mix - there are
pockets of lean and rich mixtures distributed unevenly and randomly in the
cylinder. Delivering a more intense spark at the spark plug helps to
overcome some of the combustion variations that can occur depending on the
distribution of the lean or rich pockets of mix in the cylinder during every
firing.
> Nowhere in this list of advantages does horsepower,
> responsiveness or any other performance word enter the
> discussion. If you are racing, then you want maximum spark
> so that your plugs will fire no matter what, and it would make
> sense. For street with our older cars there is little reason to
> do it other than the "Gee-whiz" factor.
What? Power output and engine response are not affected by the intensity of
the delivered spark? That might be true if you do not adjust your plug gaps
to take advantage of the greater voltage that the high output coils can
deliver. I recommend a .035" gap on cars running with Lucas Sport Coils,
this is a pretty sizable increase over the stock gap.
The simple fact is, if you have a higher output coil you should be able to
run a wider plug gap. If you can fire the spark plug across that wider gap,
the spark that is exposed to the cylinder is larger. A larger spark has
everything to do with the rate that the flame front moves in the cylinder,
which does have a positive impact on power and engine responsiveness. Spark
intensity also has some impact on the point that peak cylinder pressure
occurs and peak cylinder pressure itself. Cylinder pressure on the power
stroke is the sole reason our cars move forward.
Now on a TR6 any power increase or change in engine responsiveness or power
is likely to go totally unnoticed and there may not even be enough of a
change in either to measure the results on a dyno.
So there you go, in theory and on very advanced race engines - like Formula
1 engines - spark intensity is something that should not be overlooked. The
more intense the spark the quicker you can light off the mixture, the faster
the flame travels through the combustion chamber, the more peak cylinder
pressure that is developed... all of which increase engine response and
engine power. You can run less ignition advance with a very intense spark
also, which can be advantageous in tuning the point that peak cylinder
pressure occurs... to take advantage of the pressure's mechanical advantage
on the crank shaft.
Kai (who probably just wrote more than anyone cares to know about ignition
theory)
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