Finally deleted the cat on my 08 LMM Duramax.

It already had a 4" MBRP DPF and Muffler delete by the P.O when I purchased the truck.

Also running an AFE intake along with an Edge Evolution RACE Tuner set on Level 3.

Instead of buying a new Front Pipe I opted to save a few bucks and just knock the guts out of the factory CAT.

Overall it wasn't a very lengthily or difficult project, after wrestling with the front pipe for a while I realized the exhaust mount on the tranny had to come off. Once removed it slid out pretty easy.

I just knocked a few holes in it with some threaded rod, once there's enough holes you can just shake it out.



Straight through:



What came out of there:



I'm surprised the exhaust flows through this stuff at all:



Not sure how accurate the fuel gains are, but I tested back to back on the same stretch of road, reset each time, same ambient air temperature, same speed, etc... Before the best I could get on the DIC was 21.5mpg, after the CAT delete its showing 23mpg.



Overall I'm thoroughly impressed, the turbo definitely spools faster, and feels more responsive.

It definitely smells like a diesel now though... the sound at idle has more of a whistle and at WOT it has a much deeper bark. I love it!

I can't compare EGT's as I don't have a probe yet, but I'm assuming it dropped a little.

I'd say it does smoke a little more but not substainitally.

Here's a quick video of the exhaust, I should of taken one before to compare though.

2008 LMM Duramax Exhaust Clip - YouTube