The website I purchased mine from says "Spark Plug Starting Range AC FR3LS"


I can't find those anywhere! Anyone have any part numbers? The heads are going on a L98, around 9:5 compression. Thanks!

 

Go to your parts store and ask for them at the counter. I think i'm using FR4LS. Can't quite remember at the moment.

 

The plug is the basic 14mm, 3/4" reach, flat gasket seat, 5/8" hex. An Autolite 3924 or 3922 (colder) is a good choice. These are the standard copper core orange box plugs.

RBob.

 

Would there be any advantages to running that colder plug? Gap them the same size as stock?

 

I would gap them the same as stock. For plug temperature range it also has to do with the engien set up. A higher rev'ing engine making more power may need the colder plug.

Can start with the 3924's and see how they look after some run time. The only downside to a colder plug is that they will foul easier. So if you go with the 3922's and they don't foul out, then you are good to go.

One of the reasons I like standard plugs is the lower cost. No big deal if you want to try different heat ranges.

RBob.

 

I run the champion RC12YC. I was using the AC FR3LS then they changed the part number to 41-xxx or something. I can read the mark on the back strap on the champions easier also.

 

The Autolite 392X plugs are set up to work with a gap of about .045". Don't want to stray too far from that or the side electrode will be at an angle over top of the center electrode (which you don't want).

I use the Autolite 3924 plugs in my AFR heads and they work just great. Heat range is usually about right for a street driven car that see occasional duty at the track. I use a different plug, however, in my 383 blower motor- I didn't want to use projected-nose plugs (which the 392X plugs are) becuase of their detonation tendencies in forced induction applications, so I found another alternative that works but has a standard non-projected nose design. (Email me if you want to know more about them- AFR doesn't offer any alternatives so I had to find my own)

 

Thanks for the help guys! I'm getting there: