In case anyone really cares...
The plug gap actually does have some small capacitance since the conductors
on each side of the gap have area and a dielectric in between. Basic
physics.
The resistor does not change the voltage that appears at the gap before it
breaks down because Ohm's law says that without current flow, there is no
voltage drop across any resistor.
Once current flow starts, that changes, but the current isn't that great and
the resistor is a fairly low value-so you really don't dissipate much energy
in the plug's resisitor.
Shielding plug wires is a standard military practice to reduce the amount of
radio noise a vehicle generates to announce itself to the enemy. The entire
plug must be shielded right down to the head also.
Racers have not had very good luck with this practice actually accomplishing
anything for them in reducing EFI computer problems
I would be afraid of changing the overall circuit operation in a car not
designed to have shielded plug wires because the plug wire shielding is also
a shunt capacitor to ground.
It will shunt some of the lower frequency alternations in the spark waveform
to ground as well as the high frequencies. It is more than just a simple
shield.
Chuck V
From: "Richard Schmidt" <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: <[email protected]>
Subject: Re: [F500] resistor plugs
Date: Wed, 11 Jul 2007 18:00:57 -0500
Ted,
I don't see the spark plug as a capacitor. It's a spark gap. The arc is
caused by the current being conducted through the ionized air between the
plug center conductor and the ground.
If we were running high performance engines, i.e. high compression, we
would
never be able to use resistor plugs.
The voltage that is supplied by the transformer (coil) must overcome the
air
gap in the plug. If you put a resistor in series between the transformer
output and the air gap, you are limiting the amount of voltage that is
expressed across the air gap when it fires. Without that series resistor,
you could use a larger air gap. Why would you want to do that ?, because
it
will result in a more efficient ignition of the fuel/air mixture around the
air gap. Think about piston driven aircraft engines. Anyone who has ever
watch a pilot go through his pre-flight, will notice that when he or she
switches one of the mags off, the RPM drops.
If you have to run resistor plugs because of interference to electronic
equipment, then you can do that, or
1. You can insist that the vendor of the equipment follow better design
practices to eliminate the interference,
2. Check your owners manual to make sure you have installed the equipment
correctly.
3. Add shielding to the plug wires.
Also don't forget, all the current the fires the plug has to get back to
the
coil some how. You should always have a good heavy ground wire between you
engine and your battery. Don't count on the frame. Make sure your coil core
is grounded with a short path back to the engine.
If you are running a Kawasaki engine, the plug wires have a resistor built
into them.
Richard
----- Original Message -----
From: "Ted Rudolph" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, July 11, 2007 7:42 AM
Subject: RE: [F500] resistor plugs
> Ed,
>
> As others have said there's no performance advantage to the resistor
> plugs. All the resistor does is knock the square edge off the voltage
> going to the plug. A square wave (or, more accurately, a spike-square
> wave) contains all sorts of high frequency energy. In the old days that
> didn't matter, but as electronics became more prevalent in the cars
> there was a need to reduce the interference caused by the high frequency
> energy (my father said it was a common way to "fix" AM radio reception,
> to give an indicator of the early real need for the plugs). In our cars
> the data acquisition systems are not happy with stray high-frequency
> energy, so the plugs will help them out.
>
> In Electrical Engineering terms, the spark plug is nothing more than a
> high value air-gap capacitor that's pushed past avalanche point. If you
> look at the coil output on the oscilloscope, you'll see an initial spike
> as the voltage builds across the capacitor, and then a drop to a plateau
> as the spark jumps & ionizes the air in the gap. The resistor in line
> with the capacitor creates a simple RC circuit. The rise time is a
> function of the resistance & the capacitance. Increase the resistance &
> you'll increase the rise time....
>
> -Ted
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of edward
> capullo
> Sent: Tuesday, July 10, 2007 7:46 PM
> To: [email protected]
> Subject: [F500] resistor plugs
>
> I am curious to see if anyone has a strong opinion one way or another
> about
> running resistor plugs with our engines. I have run B9EG and BR9EG and
> do
> not seem to notice much difference. Does running one or another have any
>
> real advantage or issues?
> Ed Capullo
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