TR55's with 18k mi
 

Color looks good....but some buildup on end of plug. Gap is now .057

I do have a MSD 6A box

Thinking of going to the NGK Iridium plug (7164) for longer life

Thoughts/Comments?

18k is a lot of miles on a tr55 plug because it's a copper core plug. With your MSD box, your plugs should be changed at 10-15k miles. One thing to know is that if you are running boost, No2 or high compression you might have an issue with knock if you run an Iridium plug. I'm not sure why that is, I have had experience in this and I know lots of people have as well. Maybe someone can give the technical info on that.

You running N/A? If so, why an ignition box with the 96 ignition?

Yeah 15k mi was typically what mileage interval I changed the 55's. My motor is NA, 11:3 compression

Thanks for the note on iridium's...likely just get 55's again

well 17 years ago I was younger and dumber and thought the ignition box would help. I have found on dyno pulls it makes no difference with or without but the box has remained on the car. I have seen no ill effects relative to Opti C&R wear but suspect the plug gap wear is affected. These plugs gap at .057 which is less than normal from my understanding

I fouled two sets of NGK iridiums on my H/C setup before going to Autolite 104's on Lloyd's recommendation. I also gap them at .035. Your gap seems pretty wide for your compression to me, but I'm no expert.

I'm glad someone said it. Autolites is the way to go.

Never had any luck with the NGK and one of them broke inside my engine. They used to wear out fast though don't know if it was the 6AL or what but Autolites didn't seem to care about having a box.

I wouldn't worry about the box I honestly wouldn't run anything without one. It does run a smoother rpms and the rev limiter is worth its weight in gold.

how does the Autolite 104 heat range compare to NGK TR 55?

The TR 55 is a 5

The Autolite 106 hotter plug?

My gap of the NGK was .045 when installed. Gap has widened with wear over 18k mi by .012.

I believe the 104s are a 4. Again, I'm no expert by any means, but I'm not running anything radical, just a simple H/C with LE2 heads and a 228/236 on a stock bottom end, and that's what Lloyd told me to run. They've been nothing but great to me.

the last # "generally" means the heat range....although Autolite reportedly is not inline with other brand cross reference.

the 106 is what is listed as a "replacement" plug for the LT1

By looking at my plug color it looks OK. I would not want a hotter plug and the last # being a 6 would indicate the Autolite 106 is a hotter plug than a 104 but compared to the TR55 IDK which of the two Autolite plugs would be the closest match

IDK if a 4 heat range plug would be to cold for my motor. It is a mild cam 383 NA

EDIT:

further search found a Autolite cross reference chart. The TR55 (heat range 5) = Autolite 605. The Autolite 104 is one range colder

After looking at my plug color more....it is slightly on the hot side. Given the 11:3 compression and the MSD box I will try the 104's and read them after several drive cycles

.....well now that I got out the wrench to swap plugs Cyl 3-8 look "normal". Just Cyl 1&2 have a more "whitish" look. All the others are a grey/tan

So heat range looks good as is (5)

.. but wondering why cyl 1&2 look as they do?

The higher numerically the colder the plug, so 5 is colder than 4, etc.

your plugs look a little hot (you want half of strap to show the heat mark - your shows the full strap). The best way to evaluate is with a new plug, WOT, then shut it down and check.

i wouldn't go bigger than a 0.045 gap, and you could go with #5 or #6 plugs (your choice of brand).

Just #1 shows heat full strap. #2 a little less with 3-8 all at 1/2 and a tan/grey color vs the more whitish color of #1 &2

I have always run TR55's in this motor...just waited longer than usual to change them. They are a 5 heat range

My understanding when using a ignition box is to not narrow the gap...if anything slightly wider.

I always gap at .050. After 18k mi these grew by .007 which is well within "normal" plug wear

had forgotten how it sucks to change plugs with headers....

You are questioning the white ash? That is oil burning in the cylinder.

....I am going with #5...."worn out plug"

Ok, but #5 is showing the condition of the center electrode; calling it worn as it is just a rounded nub. It too has some oil ash but not to the degree of #9 or 10.

I usually just run the regular tr55 I've used the IX and the platinum and for the price I just run cheap ones and replace them more often.