NGK BR8HS vs B8HS

[Darrell]

B8HS plugs are not available at my usual parts store anymore. Instead they only now carry BR8HS-10 which is a marine resistor plug. The "marine" aspect refers to extra corrosion proofing I believe.

Does the spark plug resistor mitigate the spark from output from our old points and magneto systems? I think I recall reading that in DIRT BIKE magazine circa 1975 anyway -- but I didn't always believe everything I read in that magazine:D

Perhaps the resistance between resistor and non-resistor plugs could be measured and compared with an ohmmeter...has anybody tried this yet? Will extra resistance (if any) overheat the coils?

Many thanks for your thoughtful conclusions on this matter!
Darrell
Nanaimo BC

[matt glascock]

Yes, BR8HS is the resistor version of the B8HS. The reason for introducing resistor spark plugs (and wires) in the evolution of internal combustion engine ignition was to decrease the electromagnetic interference (EMI) of radio signals and such by nonresistor ignitions. The effect is akin to running an electric drill next to an AM radio. All of this has to do with Ohms law where Voltage (V) = Current (I) x Resistance (R). Since the voltage available to "push" electrical current across the spark gap is, for purposes of this discussion, a constant, it becomes the resistance in the circuit that determines the amount of current (the principle of EMI) that crosses the gap during the spark event. Since voltage is constant, by raising the resistance the current flow, by mathematical necessity, decreases. Less current, less EMI. You read Dirt Bike correctly. Using the incorrect spark plug, in either possible scenario, will result in a weak, and possibly mistimed spark in both advancement and duration. You are also correct in that if you use a resistor plug in a non-resistor application, your 50 year old coil might not have the oomph to bridge the gap efficiently and properly which could load up and ultimately burn out your coil. That all said, I have a few pals who run resistor plugs instead of the correct nonresistor types with nary a problem. I would too - and with thanks - long enough to get back to the trailer.

[Dale]

I agree that there is going to be some difference electrically, however I have ran the resistor plugs without any visible difference in the spark nor in performance.

The original spec for the Combat Wombat was B9HV. When the HV was no longer available the only option was the B9HS (Many prefer a B8HS over the B9HS). I am sure there was some electrical/performance difference between the HV and the HS too.

As our supply runs out, I am not hesitating to run the resistor version.

[Larry S]

I agree with Dale. I've been running the resistor plugs in Ace 125R, my Super Rat, and my CW for more than a year and tell no difference.

Larry S

[matt glascock]

You're guys are not alone. I think running resistor plugs in motors designed for traditional plugs only becomes a problem if there are other weaknesses in the ignition system interfering with a good, strong spark from the secondary coil.