Hot Rods AC Spark Plugs

For those trying to figure out the numbering system.

 

Good info. Thanks.

 

Kinda off topic, but AC is the initials of Albert Champion. Yep, he started both companies. I've used ACs for years, but wouldn't put a Champion in a lawn mower.

I started working in a tune up shop in the 60's (first job). Most SBCs got R44s or R45S if they had some miles on them. The S (extended tip) plugs seem to run a little cleaner than the standard plug.

Dragrace SBCs usually got 42/43 heat range (cuz that's what Chevrolet recommended), but sometimes 44 if they tended to load up at idle. I never ran extended tip plugs in a high compression engine, because the piston dome will sometimes hit and close the gap on them.

Back to the original question, I'd run R45S and not lose any sleep over it.

 

The 39 Guy -- Thank you very much for the chart re: the AC numbering system. It's very helpful.

 

You are welcome mwhistle, I just found it on the internet this morning and since there was so much speculation about what all of the numbers and letters meant I thought I should save one on my PC and pass it on to the HAMB.