I am looking into exhaust for my truck. I will have my HTT SS 65/13/65 wheel turbo and Floor-it stage 2 pump on soon to go with my new 70hp JL Machine Injectors. I am expecting near the 500-550 hp mark and I do not want the awful drone some talk about. I think there are guys running near 800hp with the 5" so I assume I don't need that. Is a 4" good enough for me? When the turbo goes on I am going to install it with a 2nd gen manifold upside down so the future twins will be an easy swap. I will run a S400 on bottom when its all done but for now I will just make a downpipe longer to reach the top turbo. Any input is helpful for me here as I have never upgraded exhaust before. I am leaning toward the Silverline brand.

 

I would go 5", it'll make for a killer sound when you put that HTT on, and you shouldn't have to worry about the power ratings, 5" doesn't kill power that bad. You'll be fine. You may find yourself sending that turbo in for an upgrade, you might get a little toasty. See how it does first.