What is the diameter of a stock 2003 CTD including the turbo down pipe? The reason I ask is because I am thinking of straight piping my truck, but I am not sure if all I need to do is to remove the muffler and weld in a straight pipe or do I need to replace the whole pipe. I know that the tip is 4 inch but the rest looks to be smaller. Apart from the sound is there any performane or mileage gains as a result?

 

The diameter of the stock pipe is something like 3.5 or something inches from the back of the turbo to the outlet of the muffler. Been a long time since I measured mine. Only the tailpipe is necked out to 4".

You won't gain any addl horsepower from the larger exhaust but you will realize lower EGT's - those aren't a problem with a stock engine but are if you add power adders later on.

I would recommend to go with a full 4" mandrel bent system and be done with it; but adding a high flow aftermarket muffler or straighpipe will help in lowering EGTs, and will cost less $$ up front too.

 

From what I can tell, the stock cast elbow at the end of the turbo necks down from 4 to 3.5", which continues as 3.5 to the front of the muffler. 4" back from there.

If I were you, and $$$ were an issue, I think I would try to get a cast elbow off a 600 someone has put a Jake on. I think there was a 4" downpipe in the classifieds.... That and a chunk of 4" and you would be in business...