One of Larry's new Pulstar spark plugs, side-by-side with the Motorcraft plug it replaced
Notice that the two plugs seal differently. The Pulstar plug is flat and uses a gasket,
whereas the original Motorcraft plug has a tapered seat. Both plugs seem to seal fine.
Evaluating "Pulstar" Plugs
A whole new kind of spark plug... but are they worth their premium price?
as published in BritishV8 Magazine, Volume XVI Issue 2, October 2008by: Larry Shimp
Recent advertisements for Pulstar brand spark plugs have caught my attention.
The claims seem too good to be true, but there seems to be little actual data
(for or against.)
The theory is interesting: Pulstar plugs contain an internal capacitor. A
capacitor is like a battery in that it can be charged and then can store
the charge. In contrast to a battery, charge capacity is small but the rate
of discharge is very rapid. When a spark pulse is created in an ignition coil,
the voltage rises rapidly, but not instantly. At the point when the voltage
is high enough to ionize the gas between the spark plug electrodes, the
resistance between the electrodes drops nearly to zero, and the current
begins to flow from the coil creating the spark. With a Pulstar plug, the
initial voltage rise from the coil charges the capacitor. Like a dead
battery, the capacitor soaks up the charge and does not create a high
discharge voltage potential until the capacitor is fully charged. Once
the capacitor is charged, the voltage potential across the plug electrodes
is enough to instantly ionize the gas and create a spark, at which time the
capacitor rapidly releases all of its stored charge. The net effect is a
large increase in voltage with a corresponding decrease in spark duration.
Under certain circumstances, this can be advantageous, but it is not
effective in all situations.
Fuel mixtures can be lean (excess oxygen), stoichiometric (exactly the right
amount of oxygen), or rich (not enough oxygen). From the factory, modern fuel
injected cars are calibrated to run more or less with a stoichiometric mixture
under most conditions. This is because a catalytic converter cannot remove
oxygen from nitric oxides if an excess of oxygen is present. But if there is
no excess oxygen, the converter can transfer oxygen from the nitric oxides to
hydrocarbons that have not completely burned. This reduces the nitric oxides
to harmless nitrogen and converts the hydrocarbons to carbon dioxide and water.
At light throttle conditions and idle, the fuel calibration is more towards
lean because there is not enough heat to form nitric oxides. (Nitric oxides
are formed by a reaction between the oxygen and nitrogen in the air at high
temperatures.) Under full throttle, the mixture goes rich for maximum power,
and there is a spike in emissions, but this is allowed because the duration
is so short.
With a carburetor, the same trends in conditions should exist as with fuel
injection except there isn't enough precision to run at stoichiometric mixtures.
The mixture is usually lean for "factory" emissions calibrations where it
would be stoichiometric for fuel injection. The lean mixture can affect
throttle response, so for many performance applications car owners recalibrate
their carburetor to be on the rich side and not the lean side. In fact,
with many V8 conversions, the only time the mixture is lean is at cold start-up.
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Lean mixtures are difficult to ignite and burn slowly, rich mixtures are easy
to ignite and burn quickly, but not completely, and stoichiometric mixtures
are intermediate in their combustion characteristics. The intense but short
duration flash generated by the Pulstar plug is very effective in igniting
lean mixtures, somewhat more effective for stoichiometric mixtures, but has
little or no effect on rich mixtures.
Rapid ignition of the mixture is desirable. It generates more power because
combustion is completed while the piston is closer to the top of the stroke
(the smaller combustion chamber volume generates more pressure). Because lean
mixtures burn slowest, the maximum benefit of the Pulstar plug will be realized
on an engine that is calibrated on the lean side. Other ways of helping a lean
mixture burn effectively are by advancing the ignition timing (vacuum advance
is especially effective) and producing multiple sparks; such as with an MSD
ignition system. Some multiple spark systems can generate up to six sparks per
combustion cycle at low rpm which helps to get the mixture ignited and can
avoid a misfire; but the last spark is over 20 degrees later than the first
spark, and very little power is generated if the mixture finally ignites on
the 6th spark. It is much better if the first spark ignites the mixture, and
so the Pulstar plugs are useful even with a multiple spark ignition system.
My car has a carburetor which I set up with a lean fuel mixture at cruise,
but I did keep it rich under acceleration so power is still optimal. However,
the lean mixture makes for a slow warm-up (especially because I do not have a
choke), and in cold weather (below about 40 degrees) there is not enough fuel
for the cooler, denser air, so I experience some lean surging and hesitation
below about 1500 rpm in the winter. Knowing this, I was eager to try a set of
Pulstar plugs.
As I expected, the plugs made a very noticeable improvement. The engine now
idles after about a minute of running following a cold start in 20 degree weather.
Previously, I would have to wait until the temperature gauge started to register
which could take up to 5 minutes. Furthermore, the initial cold idle is reasonably
smooth. It's just at a lower rpm than it is after full warm up. After about a mile
of driving (in 20 degree weather) all signs of lean surge and hesitation are gone
and the car feels more responsive overall at all temperatures. It is obvious that
my lean mixture is burning much better with the Pulstar plugs and fuel economy
increases bear this out. On three tanks of gas (with my Ford 302) I got, 20, 20,
and 21 mpg. This was in local, not highway driving. Previously the best I ever got
under such conditions was 18 mpg, with 17 being more normal. Since the weather is
quite variable this time of year, there have been some very warm days as well as
cold days. On warm days I have noticed that the cooling fans run much less often
than before, and this is another sign of increased efficiency. Ultimately, I expect
that there will be a significant improvement in highway fuel economy (which is
typically 25/26 mpg). However, I need to take a long trip to find out, and I have
not done so yet.
While my results seem very good, I have to emphasize that it is because I run a
lean (cruise) mixture. Because rich mixtures ignite easily (unless they are
extremely rich) I do not think there will be much of a benefit from the Pulstar
plugs with a rich calibration except when the engine is cold. Furthermore, I think
a rich mixture may even damage the Pulstar plugs. The internal capacitor builds up
very high voltages and if the plug has high resistance deposits on the electrodes,
the voltage may build up further before the plug fires. These excessive voltages
can break down the internal insulation. This is supported by the warning with the
plugs about the importance of not exceeding the recommended plug gap. (A large gap
also increases the voltage.)
In summary, Pulstar plugs can be very beneficial for a carbureted engine that runs
slightly lean (and perhaps for a fuel injection system), but not for an engine that
runs rich most of the time.
Editor's Note: Larry advises that after submitting this article, on the long
trip to and from the BritishV8 2008 meet, his average fuel economy improved to
between 27 and 28 mpg. With the previous spark plugs Larry would have expected
between 25 and 26 mpg.
Disclaimer: This page was researched and written by Larry Shimp. Views expressed are those of the author, and are provided without warrantee or guarantee. Apply at your own risk.
Photos by Larry Shimp for BritishV8 Magazine. All rights reserved.
