Can meaningful spark plug readings(for timing) be performed thru typical street driving or can they only be made at the track? I realize this is only one plug from eight but the marks are similar on all. Total timing on my 9 to 1 compression(bumped slightly from 8.4 to 1) 455 Pontiac is 36 degrees all in by 2800. For full street driving transparency, vacuum advance is 8 degrees at 15"Hg. The total timing mark is past the 90 degree bend on the strap. Does it look too far advanced? In regards to the black spots on insulator no detonation can be heard. I could be wrong but I believe this to be from oil consumption due to my factory forged pistons. (I get piston slap at cold start-up.) My car, SD-455, came from the factory with the assertion that oil consumption would be higher because of this. Am I ok or do you think I should back off 2 degrees or leave it alone since it is running great? Thank you.