RCignition said:
The resistor in the cap is not what stops the radiation..The metal cap and shielded wire alone do this..NGK makes a bakelite resistor cap to use with the CM6 spark plug.

That's true, but the resistor minimizes the strength of the EMI created by the secondary side of the ignition. Having a resistor and a shielded ignition is kind of like wearing a belt and suspenders. The resistor might also be protecting the electronic circuit inside the ignition box.