All things being equal, a more powerful spark will create higher
cylinder pressure which will create more power. The power of a spark is determined by its
voltage (more voltage = more powerful spark).
Aside from variables such as cylinder pressure and A/F ratio, the
amount of voltage required to jump across the gap of a given type of spark plug is
determined by the plug gap. A smaller plug gap requires less voltage to jump across the
gap and a larger plug gap requires more voltage to jump across the gap.
There is a way to reduce the amount of voltage required to jump
across the gap of a plug. By increasing the number of sharp edges that the spark can jump
from and to (as in SplitFire and Torquemaster plugs) or by using an electrode material
that is a more efficient conductor than the standard steel material (like platinum) you
can decrease the amount of voltage required to "jump the gap". The only problem
is that these "specialty" plugs will produce a less powerful spark than a
standard plug will at the same gap. This means that, as long as your ignition system can
provide enough voltage to jump the gap on the spark plug all of the time, with these
"specialty" plugs installed in your car your engine will produce less power than
it will with standard spark plugs. The only way you can regain the power lost with these
"specialty" plugs is to open their gap out farther (a wider gap requires more
voltage to jump the gap).
I've seen a number of cases where people have installed SplitFire,
Torquemaster or platinum plugs in their car in the place of standard spark plugs and have
complained of reduced power. In all of these cases the specialty plugs were installed
using the plug gap specified for the car's original standard plugs (with the exception of
the Torquemaster, whose gap is not adjustable). The reduced spark power due to the reduced
voltage requirement of these plugs was the culprit.
Nissan DID address this problem by specifying a larger plug gap when
using platinum plugs (0.039" to 0.044") instead of standard plugs (0.032"
to 0.035"). In this case, the platinums will produce roughly the same spark energy as
the standard plugs while providing an extended service interval (50K to 60K miles for
platinums versus 20K to 30K miles for standards).