Originally Posted by SouthArk370Z

Backfiring is usually the result of a very rich A/F ratio and the ECM has to be tuned to cause the overly rich condition, which overloads the cat, which allows raw fuel to pass to the tips, where it ignites. The exhaust system doesn't cause backfiring unless you remove the cats.

For a "regular", non-backfiring 370Z, a tune is not required if you make only exhaust mods or only intake mods - the ECM will adapt. If you make both I & E mods, you need to get a tune.