123 ht leads

[DT]

I have a 123 ignition system with silicone HT leads and a sports coil. I read that I need a lead separator to prevent cross over in the cardboard tube. Is this really needed as surely the 123 only gives more accurate spark timing not greater voltage which is generated by the coil. Advice and experience welcome please

Thanks

David

[Heuer]

No you don't. Maybe on a race car separating the leads is worthwhile but on a road car, no. Stay with what you have and enjoy the car.

[PeterCrespin]

I have a 123 ignition system with silicone HT leads and a sports coil. I read that I need a lead separator to prevent cross over in the cardboard tube. Is this really needed as surely the 123 only gives more accurate spark timing not greater voltage which is generated by the coil.

Yes and no.

The coil is basically a step-up transformer and the spark voltage is governed somewhat by the ratio of fine turns in the secondary (HT) winding compared to the number of turns in the primary low tension winding connected to the points or 123.

However, the physics of induced voltages require rapid switching of the primary coil as when the points open and the current collapses. Electronic switching is far faster than mechanical, so even with the same coil an electronic system will give a fatter spark - which is why starting usually improves.

Naturally, what goes up must come down, as they say. The sharper higher voltage pulse fed down the plug wires is not only more efficient at firing the plug but also more efficient at inducing a stray pulse in any adjacent conductor such as the plug wires running alongside, leading to cross-firing. The tendency to cross fire depends on how closely and for how far the leads run together. I forget the maths but the tendency to induce transients between neighbouring conductors probably follows the square rule so that doubling the separating distance reduces induction by four times. Something like that. therefore even a thicker insulating covering on each wire will help significantly. You will probably be perfectly OK but it's wise to keep an ear out for high speed misfires and look for arcing under the bonnet at night (not feasible with wires bundled inside an opaque conduit). My personal choice would be to use the XK style six-hole disc separators every 6 inches, rather than the conduit. They look almost as neat.

Pete

[DT]

Thank you for this explanation and advice

I think I will try the usual lead carrier and see how I get on

David