Packard Forum Index » Post-War (1946-54)

On a 51 to 54 would is most common? Book says Chamion J8 or AC 46. Some use Autolite 308 but it crosses to a J12. I have a set of unused J12's are they ok to use even though they are hotter than an AC 46? What is suggested?
Thanks
John

What kind of driving do you normally do?

Most types. Around town to interstate.
John

My 53 Cavalier's 327 has Champion J11C plugs in it. They were in the car, and new, when I bought the car. If I remember correctly, I had checked with the group and there was no reason to change them.

Checking online, Champion says the higher the number, the hotter the plug. J12 should be hotter than J11C. My understanding is, and someone can clarify, running too hot a plug could cause pre-ignition. Too cold a plug and you may end up fouling plugs. But is J12 too hot??? I'm assuming it makes a difference what octane fuel you're using as well.

Sorry, more questions than answers!

I recently had my plugs out and they look okay to me, and my car has been running well.

AutoLite 306 good for a normal mix of local and higher speed highway driving.

How do you choose the correct heat rating of plugs?

Thanks.