AR3924 vs. 3924 autolite
 

Curious if anyone is using the AR-series plugs in a street application. I just replaced my RC12YC plugs in my edelbrock 87 cc heads with the regular 3924s. The old plugs were pretty heavily carboned up, although that is probably a tuning issue. Has an MSD box triggered by a R2R with a blaster 2 coil.

Do the AR series plugs produce more complete combustion, prevent plugs from loading up? How long do they last with the cut-back electrode? I guess i'm probably looking at a plug change every 10k miles anyway, is it worth giving the AR plug a shot?

I use the regular 3924's. The AR's just have the ground strap cut back over the center of the electrode.

I simply cut back the ground strap on the regular 3924's lol

The AR series plugs have the cut ground as mentioned and a nickel coating on the shell that looks nicer and possibly reduces exterior rust on the shell. Functionally, they are the same. If you have some fouling issues, you could try a 3925 or 3926 which are 1 and 2 steps hotter.

Yeah I am pretty sure the distributor tune is fine, will work on leaning out the carb a bit and see how it goes with the 3924s. Who knows, maybe a nice long drive with a few WOT runs would have cleaned the old plugs up? Plus it's not very warm here yet.

Still curious how much of a difference those cut back electrodes make on the AR series plugs?

The spark wants to jump from a sharp edge to a sharp edge. The cut back electrode allows that to happen more out in the open. HP wise, in dozens of back to back dyno tests, I have never seen ANY difference in HP or torque that wasn't within the window or variation for the dyno. This includes heat range variation of 2-3 steps. Maybe there is 1/2-1 1/2 HP difference? But how do you know it's for real? Engine Masters video's report the same basic results. But these tests are not long term, taking into account choke start-ups, extending idling, cold weather operations. The right heat range plug will maintain optimum performance longer. HP increase, you will need to find it somewhere else.

Thank you. I wasn't really looking for more power, just to see if drivability improved or maybe plugs stay cleaner from more complete combustion.

I figure anything you can do to help the combustion process is a good thing.
I've never dyno'd the change myself so can't comment, I just do it for the simple reason of trying to get the spark out from under the ground strap a bit. Something I've been doing for a couple of decades on any plug that I run.