22-10-2024, 09:00 AM
Adding suppression in the form of resistance in the leads, or resistive plug caps, has the disadvantage of less reliability. Rather than going through the resistance, the high voltages involved (thousands of volts) will not reach the plugs but will short circuit through the slightest crack in the coil neck, crack in the distributor cap, or crack in the rotor arm. With the addition of the slightest bit of condensation (damp) the high voltage might short circuit by tracking across the surface of the distributor cap, or short circuit through the slightly porous insulation on the older HT leads.
As resistive plug leads were introduced in the 1970s and became old in the 1980s the insulation became porous and the problems of not starting due to damp weather became worse.
To me, there seems a big advantage in copper leads and plug caps. Resistive leads with good insulation are ok when new.
As for coil resistance, there are plenty of options. Standard 12v coils of the 1960s are 3 ohms. 12v coils designed to use with a ballast resistor are generally 1.5 ohms. And 12v 'electronic ignition' coils fitted as standard to cars in the 1980s into 90s were 0.75 ohms. Standard 6v coils are probably around 1.5 ohms.
Aftermarket electronic ignition systems can be designed to use any resistance of coil chosen by the designers.
Me, I use 12 volts, with a 3 ohm coil, points and condenser. This was good enough for Austin throughout the 1950s, 60s and 70s, so it's good enough for me! Regarding radio suppression in those decades, I believe the carbon sprung contact in the distributor cap had some resistance in those days.
As resistive plug leads were introduced in the 1970s and became old in the 1980s the insulation became porous and the problems of not starting due to damp weather became worse.
To me, there seems a big advantage in copper leads and plug caps. Resistive leads with good insulation are ok when new.
As for coil resistance, there are plenty of options. Standard 12v coils of the 1960s are 3 ohms. 12v coils designed to use with a ballast resistor are generally 1.5 ohms. And 12v 'electronic ignition' coils fitted as standard to cars in the 1980s into 90s were 0.75 ohms. Standard 6v coils are probably around 1.5 ohms.
Aftermarket electronic ignition systems can be designed to use any resistance of coil chosen by the designers.
Me, I use 12 volts, with a 3 ohm coil, points and condenser. This was good enough for Austin throughout the 1950s, 60s and 70s, so it's good enough for me! Regarding radio suppression in those decades, I believe the carbon sprung contact in the distributor cap had some resistance in those days.