In a perfect world , no exhaust . My 2015 Cummins, would go into limp mode every 5-10000 miles. Dealer says get on the highway to regen . I just drove with rv 2000 miles ! Does that count ? Had to get on highway to get to dealer ! Then egr is clogged , too much city driving , impossible, it was cleaned 3 times, took major fighting to get them to cover it under warranty . 36,0000 miles it does it again , this time they want to clean the whole system over 2000, even though it was a known problem , for less I did the delete, never had another code, limp mode ( 300 miles from a dealer with rv , last time ) I drive very easy , my engine will not put out black smoke like the older ( 2007 and before) models , drive 69 , I get 22mpg, 2015 tradesmen crew 4x4 long bed , stock tires, never back to the dealer since then .
Makes no sense to put exhaust back into an engine.