A Champion J8C alternative may be cheap at Walmart, but according to the Techs at Champion......

[Semmerling]

they are the wrong plug.

 

Champion was/is recommending a "10-11" heat range for the mid '30s and forward. They are recommending a J11C (RJ12C if you have a radio) for a cast iron head. Both gapped to 0.025.

Aluminum head uses is a recommended H10C...with radio its RH10C. Again both gapped at 0.025

I was surprised when the subject of bargains on the J8Cs came up as I have plugs here going way back and the lowest is an 11.
Given that I called them and asked and the guy with the most history there, he said that it was never J8C.


 

Edited May 15, 2023 by Semmerling

[Sniper]

hmm, so I dug into my Parts manual.

 

46-54, iron head, calls for an Autolite A7 plug, which crosses to a Champion J8C.

 

https://www.sparkplug-crossreference.com/convert/AUTOLITE/A7

 

So Mopar recommends a J8C, essentially, Champion doesn't.

 

Simple test, run the J8's, if they don't stay clean run a hotter plug. 

 

I run the Autolite 306 plugs, which crosses to a Champion RJ11, they don't seem to be a problem, but if I were pinging I might drop down to colder plug.

 

 

 

[Booger]

Autolite 306

[desoto1939]

Here is an Autolite Champion chart. from around 1939.

I willhave to look in my Champion Catalog but I think the J8 got superseded to the J8C.

 

When i find my Champion Catalog I will post.

 

Rich Hartung

 

[Plymouthy Adams]

your friendly Plymouth (1946-54) factory service manual lists the standard plug to be gapped at .028 and if you running resistor plugs, gap these to .035