I have some autolite 104's now and I just pulled them for the first time in a year and they are tan at the tip and browner toward the bottom which I though was normal. The threaded part that faces the chamber is black and has shoot/carbon. Is that normal or should I go hotter? I was thinking about trying a 105 or TR55. Do you guys think thats too hot for 14psi?

There was no detonation with the 104's but I am debating on a hotter plug improving driveablilty and possibly lowering my 60ft. It only sees the track about once a year.

 

im running the 104s as well it about 5-6psi and im curious as too other plug options as well or should just stick with these?

 

You can't read them that way and get any meaningful data unless there are some obvious signs of fouling or overheating or detonation. One problem is that the additives in the gas can color the plugs. You can only do it with a new plug at wot, then cut it and read the plug. You really need to disassemble the plug and look at how high the carbon ring is on the insulator or use a thermocoupled plug. Basically, you need to run the coldest plug that won't foul during daily driving, or else switch plugs when you go racing. It's tough to get a plug to work on putt-putt street duty, then also work on 12 psi boost WOT and be in the right heat range, but the extended tip designs work best for a wider heat range. Too bad they're so hard to change on our cars, huh? I am in the same boat, trying to figure out which plugs are best for my AFR headed 383 and Vortech blower.

 

Kevin you summed up what I was thinking today, I'd like something that runs clean and can handle 14psi. I am gonna give some 105's a try if I can find a set.