I would like your opinions, I need a new cat back exhaust. If it was for a stock block 231 I would just go with a 2.5 ATR. Hopefully (if done) I will be putting in a 274 TA headed oncenter motor next summer. Will a 3.0 ATR sytem be needed? If I decide to go with a 2.5 system for noise how much HP might I be giving up? 2.5 vs 3.0 has been discused for stock blocks but I could not find any information about it's use with a stage motor. A single 3.0 would just be too loud.