mandrel bends are only to get the maximum performance out of your exhaust, for your 105HP 4cyl Diesel, its not going to make any difference whatsoever. you've already upgraded the size by a decent amount and with no cat/muffler it helps even more. All I am running is a high-flow cat and it has a nice sound to it but at WOT it barks pretty good. I've never felt my truck with factory exhaust so I can't compare....All I know is I'm happy with it.