Spark plug number deciphering

[Donald O.]

RJ12YC

R = resistor type
J = ?????
12 = heat range, but is a 14 hotter or colder
Y = ?????
C = copper/nickel ????

Is this comparable to an AC R45?

DonO

[Leif A.]

Re: Spark plug number deciphering

R - resistor type
J - 14mm thread, 3/8" reach, 13/16 wrench
12 - heat range
Y - standard nose
C- copper design

And, yes, the AC R 45 is the comparable plug.

[Duke W.]

Re: Spark plug number deciphering

No, they really aren't even close. What is the application - year and engine, and why Champion?

Duke

[Leif A.]

Re: Spark plug number deciphering

I stand corrected. The comparable AC plug would be AC 41-627, AC FR3CLS, AC FR2LS just to name a few. Is this a lawn mower plug??

[Larry M.]

Re: Spark plug number deciphering

I stand corrected. The comparable AC plug would be AC 41-627, AC FR3CLS, AC FR2LS just to name a few. Is this a lawn mower plug??

I KNOW RC12YC is a lawnmower plug for my Snapper mower. However, RJ12YC I believe is for MOPAR applications: I recall that my old 383 HP wedge engine took J12Y plugs. This is back in the mid-1960's before Resistor plugs and Copper core plugs became standard issue.

Also, increasing the number from 12 to 14 gives a hotter plug. The 2 bbl engines ran the 14 heat range, and the HP 4 bbl engines ran the 12's.

Larry

[Patrick T.]

Re: Spark plug number deciphering

Don, we both have the same engines in our '67's and I've tried many different plugs. The plug that worked the best for me is an Autolite 290. I've tried the AC 45 and 46 plug's and there is no comparison. The 290's are cheap, give them a try. PT

[Domenic T.]

Re: Spark plug number deciphering

Don, we both have the same engines in our '67's and I've tried many different plugs. The plug that worked the best for me is an Autolite 290. I've tried the AC 45 and 46 plug's and there is no comparison. The 290's are cheap, give them a try. PT

I had the best luck with Autolite at the strip. One friend said Champion seemed to work good till the plating wore off. AC 44 seemed to be avarage. We put 45's in pops car.

Dom

[Donald O.]

Re: Spark plug number deciphering

No, they really aren't even close. What is the application - year and engine, and why Champion?

Duke

Because I like Champion and will not use ricer plugs in my Corvette