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best to do it with heads off engine. get them all the same indexing positions that way with no doubt. then # the plug for install later.

i noticed a smoother idle and running engine. it will help performance. how much? results will vary.

over kill on a daily driver IMHO, on an all out high HP engine, they still do it today on the bigboys. yes,you may need a few set to get 8 out of them.

would i do another engine? sure. if time and budget allows for it. i like tinkering with stuff like that on the bench to keep busy when building engines. in the car with headers on? i would not bother.



I have never seen it done in the alcohol or nitro classes. I used to go through 16 plugs per run before going to one mag, it would take way too much time to index them in a hemi and would be waste of time imo. We only get one run per plug because we read them very closely after each run.I could look back at the whole weekend through my plugs and computer, they are very important tuning tools.

I kept a guy busy doing nothing but gapping plugs and dropping the oil. That all he did all day and was plenty busy without indexing plugs.