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?