[Christ]

Heating a wire changes the latency of the signal it provides. That said, it's probably only by a few ms, not quite something that's going to make or break efficiency.

On any engine, the "signal" wire to the distributor is also known as the "coil" wire. It provides the extremely high voltage charge from the coil to the distributor.

While heatshrink tubing will do nothing to keep heat away (it's has nearly nil for insulation properties), wrapping your wires with canvas-backed mylar does help keep heat away from the wires, changing your ignition timing by a few ms, which might mean something if you have a sensitive engine.