Looking at the source-auto twin parts they have a 5 inch down pipe for $190 but then they have a piece that fits into the s400 so you can use a 4inch for 60. Would you notice a big difference for 4 to 5 inch DP?? Also With the backing plates What the difference between the divorced, machined, and the regular one

 

got a link?

 

http://www.smokindiesel.com/

 

The S400 has a 5" outlet, so you would need a 5 inch downpipe. I do have my 5 inch downpipe running into a 4" exhaust, and it works fine. I don't think you would gain much, hp wise, with a 5" exhaust until you reach 600hp.

I'm not sure what "piece" you are talking about that fits into the S400, but I would guess that you are talking about the plate that attaches to the hot pipe. They have these in 3,3.5, or 4". You would use the one for whatever size hotpipte you are using. In other words if you had and hx35 with a 3.5" exhaust outlet, then you would want the 3.5" S400 plate, with a 3.5" pipe from the 3.5" backing plate.

The difference in the backing plates, are: the divorced one has an external pipe welding in for the wastegate hole. The machined one, has a grove machined into the backing plate, so that there is a larger passage for the wastegate gases. The regular one, is basically the standard flat backing plate.

I hope this helps...
Paul

 

Source Automotive

 

Rip Rook himself told me that @ something like 620hp, he lost 11 hp going from 5" exhaust to 4" exhuast...both muffled!

11hp is nothing for a truck you drive a lot That being said, I love my 5" straight from turbo to tail

Chris