The most common plug used in racing is the NGK R6725-11.5 heat range. Expensive to buy but Mazda gifted those to racers so my guess is that Mazda thought them to be the ones to use.
Before Mazda we used Champion N-57-G (gold palladium) fine wire center electrode. That is an old number so you have to check with Champion to get a current number.
Champion gave those away to racers as well. Never a problem. I gave those to piston powered racers who had trouble with running street plugs in race cars.
My ignition system was two MSD 6ALs with plugs gaped at .010" to .012". Both plugs fired at the same time. MSD Blaster coils. 1984 Mazda electronic distributor with
no vacuum advance and advance weights brazed solid. Start and run on full advance. (9,700 RPM rev limiter chips). Never a problem. This causes more than 50,000 volts to the plug.
One day I was adjusting the idle oil pressure on the dry sump pump while warming the engine for the first session of the day. I got my left hand too close to the front leading plug boot. The last thing I remember was that a bright blue lightning bolt extended from the silicone plug boot to my Twistoflex. I took a short nap. The crew guy shut the engine off at 190 degrees as usual.
If you have a pacemaker, do not screw with an MSD or a Mallory HiFire.
Any Question-Any time.
Lynn E. Hanover
In a message dated 5/16/2020 7:23:08 PM Eastern Standard Time, flyrotary@lancaironline.net writes: