I have a 2001 but installed a 98 block and head. stroked..removed coil rail and installed coil pack and wires...I assume I should use spark plugs for a 98?...they are a different part from the 01 plugs...why should they be different?

 

not sure if I answered my own question but I went to the champion website and looked up the lengthy specs for both plugs...they are totally identical EXCEPT for the gapping...the 412- 98 and down has a recommended gap of .032-.038 the 438 for 99 to 01 has a recommended gap of .033 to .037...makes no sense since the 99 engine is identical to the 98...the heads don't change until the 2000 year...So since I already have a box of the 412's I will put them in and see what happens...I will let you know

 

You knew this wasn't going to be easy....the plugs I took out of the stroker were autolite 985...they are good for EVERY year Cherokee from 92 to 2001...I think I put them in when I replaced the 0331 head in the original 01 with a reman 0331 sometime last spring...they only had 5 or 6 thousand miles on them so I reused them in the stroker in case I had fuel/ air mixture issues in the stroker and I didn't want to foul brand new plugs. They showed no signs of running rich after 5 or 6 k in the stroker with 20% larger injectors so everything seems to be burning well. There is much more ceramic in the Champions then the autolites and I found a picture from a year or two ago when I replaced the 01 motor spark plugs with the 438's RC12ECC as listed...they look identical to the 412 RC12LYC that I put in today as far as the extended ceramic...I can't remember my basic automotive schooling...does more ceramic make the plug hotter or colder? Bottom line...If I have any issues...pinging or knocking...I will go back and get the autolites SO if autolite 985 are good for every 4.0 then there cant be any differences in the heads or coil rail/distributor configs...and the Champions are identical except for a minor gapping differences so it probably makes NO difference what you throw in there...Im no exper but I did sleep in a holiday inn express last night...LOL

 

Did more research...according to google.....more ceramic makes the plug hotter....less ceramic makes the plug cooler. If the autolite 985 are good for EVERY jeep from 1991-2001 and have short ceramic and both the Champions have long ceramic and have the same heat range between them...are the champions the same?.....Champions list both plugs as a heat range 12...………...Autolite lists their heat range as 25.......Google says that heat ranges are not comparable between different manufacturers...I know in the stock 2001 I ran BOTH champions and autolites and they all came out looking similar at the end of their life...so a whole days work ends in no definitive answer...for 15 bucks I will pick up a set of autolites to keep on hand just in case...hows that for confusion

 

The protusion into the combustion chamber isn't exactly what determines the heat range. The contact inside the plug end and into the threads in the head dissipate the heat. I run champion 344 (RC9YC) from the renix years in my turbo motors.

 

Why did you choose that plug...was it trial and error...I did a check on your plug at WWW.CHAMPIONAUTOPARTS.COM...Identical to the others EXCEPT your insulator projection is 0.06in compared to the others at 0.029...and thus you have a cooler plug at a heat range of 9 compared to the 12 of the later plugs...probably a good choice since Im sure your turbo probably runs hotter than my 10.something ish compression stroker...I ran these 412's in my old 92 stroker and had no issues now that I think back ...I am probably WAY overthinking this...…...