I am thinking about getting a new exhaust system this summer for my 1999 Cummins and can't decide whether to get a 4 inch or a 5 inch pipe. I was wondering if there was any benefits having the 5 inch, rather then the 4 inch i.e sound, horsepower, torque, etc. I was also wondering what the best brand is as well. If you have 1999 can you let me know your experience with your new exhaust.

 

I am newer. However talking with Sinister diesel tech. 5 inch has a tendency to drone. No performance gain with 5 over 4. I do believe 5 will help lower EGT's. How much not sure. I went with flow pro. Check amazon, there is a company in Canada. DPF performance, they were the cheapest and didn't charge shipping.

 

No real gains with the 5" until you're making a ton of power. There will be a bit of a tonal difference, matter of personal preference. Your best bet is to find people locally and see what you like.

Diamond Eye makes some inexpensive stuff - turbo back 4" for $250, free shipping from thoroughbred diesel. 5" bumps that up to $400.