st and lt knk

[aaron68]

I have a 2014 charger rt with mopar cai and cat less mids. I put the 91 tune on and tweak the wot fuel and wot spark both ways but no matter what I do to the car the computer always pulls timing and makes the same afr. ive had it on the dyno multiple runs tune or no tune and actually saw same hp and tq regardless of using the tuner or not. I always get from 2 to 5 st knk no matter what. how can I fix this and actually use the tuner to dial in my car and get sum power gains

[Mike_Levy]

The catless mids are most of the problem. Its been dyno proven that the Hemis need back pressure. Removing the cats kills that.

And what kind of gas are you running? BP, Exxon, Mobil or Sunoco is recommended. Shell will always knock.