Heat Range Experts: What plug to use?

[OlDuster]

I know the 'manual' lists a N13Y for the 8.6 360 and a N9Y for the 10.5 340. When we machine and rebuild these engines, what plug range should I use? I have a 9.5 340 and a 9.4 360. My 360 is missing occasionally and I am running the N9Y Champions. I think they are too cold a range for the 9.4 compression. I am using a Bosch Platinum plug in my 340 and it runs fine. It is the same "range" as the N9Y. What plug should I put in my new 360. I have about 150 miles on it and will start to work it a bit, soon. I am wondering if a N10Y would warm it up a little and stop the fouling. N12Y? What do you guys run on these street motors?

 

[EvilScamp]

I'm running N12Y Champion in my 340.They work fine for me never had any problems with them.

 

[six pack]

See if you can find some RN11YC's but do not use a bosch platinum, these are junk in a Mopar. I have removed too many sets for customer that came in with misfires.

 

[OlDuster]

EvilScamp: What is your 340's compression ratio with the N12Y? I am thinking that a set of those will work in my 9.4 360.

SixPack: What about the RN11YC plug in the 340? What compression ratio are you putting these plugs into. Maybe I should try that in my 9.5 340 instead of the Bosch Platinum plugs.

 

[six pack]

I know the heat range was 10 for most of theMopar muscle cars that were over 10:1 compression.
RN11YC were used in the mitsu 3.0L engine that had 150-160 psi cylinder pressure so I would think they would probably work well for your application.