MTFCA Forum

For those who are using modern 14mm spar plugs: What brand are you using? What plug number are you using (heat range)? Are you using a copper core or platinum core plug?

If you are running coils and magneto suggest staying away from plugs that have "R" (resistor) in the number, they don't seem to hold up as well (I don't think the resistors like the voltage going up and down), but will work. Non-resistor may need to be special ordered as no longer an on the shelf item from what I have found. Reach may depend on what head and how far you want them to extend in.
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I’ve always had good luck with the copper core NGK BP7ES. Have also run the lower heat ranges BP “5” and “6” ES when on the shelf in a pinch. 14mm x 3/4” reach

I used to run platinum plugs, and they worked fine... but they seemed to only like running “lean”. In my experience, they fouled easily and cleaning never seemed to bring em back to life. And at about $10 a pop... I’ve got a whole drawer of dead ones to show my stubbornness

I still foul the copper cores on occasion, but rarely compared to the platinums. And if one does foul, I can usually get it back with a simple brush cleaning

I don't know if it was the lack of reach, or what, but I once fell into the trap of using adapters and modern plugs in a standard T head on a stem-winder. After spinning for an hour with rest breaks interspersed, I barely got a "chuff" out of it. I put a cleaned up set of 90+ year old plugs and it lit of on the 3rd pull. That set of plugs is still in the car 9 years later and run great.

Perhaps in a high compression head, at the correct spacing and reach in the combustion chamber, modern plugs are the berries, but I would never advise someone to try them with adapters. Just my experience. My perspective is that if a plug has lasted for 90 or so years, is freshened up and gives 9 more years of service, why on earth would I want to mess with a modern plug that looks ugly to boot?

After 15 or so years heavy in the hobby, I have pretty much given up trying to incorporate "improvements" to my cars. The result is I have more $$ in my pocket and my cars tend to run better and longer.

Sorry to hear of your negative experience with the 14mm plugs Scott. While I do agree that stock is simple and reliable, there are those of us that just have to tinker. I have ran 14mm plugs in HC heads and also with adapters in stock heads, and have always had decent results... even considering my platinum plug period

In all fairness, I have always had distributor, high tension magneto, or modern HEI type ignition on my cars too... so may not be the best character witness for stock ignition

Kevin

It might be just as simple as having a more modern ignition like you mentioned. I was attempting to start on 12VDC through original rebuilt coils FWIW.