its an 02 z28 w/a 408ci ran execellent with 1st tune. It already has a tune for cam full exhaust and 93 octane, I recently put true dual 4inch x 4feet exhaust with flowmaster 1 chamber mufflers on it. I Now run 112octane and changed the rearend now it has 4.11. The car runs good until 3rd gear topend about 4800 rpm its starts popping. need some suggestions.

 

what plugs? gap?

Do you have a scanner and can post a log file?

 

will post log file tonight