Spark Plugs - Again!

[Stumper]

I'm sure this has never been posted before - looking for plug recommendations on my motor. Motor is a stock stroke 440 ci with around 12:1 CR, using Indy 440-1 heads, a Lunati cam with .674" of lift (at 1.6 rocker) and duration of 278 / 286 @ 0.05”. I run 93/110 mix fuel to about 95.5 octane
These are 14mm - 3/4" plugs

I have run Autolite AR3934 and AR3935 in it before and currently have Champion 792/C59YC in it. For street use they all foul pretty bad. Thinking of going up to Champion C61YC on next set but I'm wondering if I should just jump to C63YCs or if they might be too hot for street use? I'm pretty sure I'll never find a plug that doesn't foul in this motor in street use but would like to find something tolerable. Suggestions - or watch outs????

 

[68sportsatelliteragtop]

What are you running for an ignition system?

 

[cdr]

sounds like its to fat in mid range from huge cam

 

[shag766]

this is over my head, but, get rid of the champions. thats a personel opinion. they are like ********, everybody has one. honestly, in my opinion, you will end up with one that you are comfortable reading. i learned this racing snowmobiles. 2 stroke. rick

 

[Ron 73]

Ive been checking on different plugs for my car, its just a 318 with a mild cam in it and i only have a problem with fouling once a year and i just don't drive it all that much. Once a year is to much, ive set the carb, ive had someone who knows them set it and still have the problem, bought a new carb same thing, maybe its my luck maybe im doing something wrong but with champion plugs i don't care what i use them in they foul, i tried them in my tractor for plowing snow and had problems so i went to Ac-Delco and no more problems. I have Auto lites in the 318 now and its been a year plus and just now starting the problem again, with Champs i had to replace them twice a year, this isint going to start a debate im just saying my piece on how they are with me, i know a lot of guys have luck with them. Im hearing great things on Accel plugs and been thinking of trying them. Maybe someone hear has tried them and can tell you how well they work (Accel)...

 

[Stumper]

What are you running for an ignition system?

Ignition is MSD, 6AL box and billet dist.

A year or so back when I ran the motor on the dyno with AR3935s they came out after a couple of pulls looking good - so for WOT runs on 110 fuel I'm sure that is a good heat range.
Runing on the street with 95 octane they foul up pretty bad. I know it has to do with the big cam and tall single plane intake but trying to see if I can find a happy medium.
I think the AR3935s cross reference to more like a C61YC Champ? Maybe C63???
Anyone know the difference between a Champ C61YC and a C61CX?? Been looking at their site to find the difference but nothing so far...

 

[Stumper]

Found some answers to my own questions I think. The difference between the Champion CX and YC is the YC is a projected center electrode while on the CX the ground electrode is cut back. These differences are designated on Autolites with just different numbers (ie AR3911 = AR3934 in heat range but the 34s are cut back).

I guess my next question is if I am better off with a regular ground or a cut back ground?