I have a e99 PSD and would like recommendations for exhaust upgrade. I have and automatic trans so I have the cat and still have the stock 3.5 inch pipe and muffler.

Could I just cut the cat out use the Summit Racing slip pipe there and do the same and delete the muffler giving me a 3.5" thru pipe w/o muffler. And then when I get ready to go aftermarket exhaust go up to the 5"? I could do this for <$100 and then work the other efficiency/ power mods that would benifit from 5" and skip the 4" exhaust step all together. 3.5 to 4" only gets a 25% diameter improvement.

What are y'alls thoughts

 

It's closer to 30%, and there really isn't any benefit to going to a 5". I'll find the thread here in a second. It's got great info from the guys who have experience and data.

 

Here is the thread For those considering big exhausts...

Then there are those that think stock exhaust is good enough. I have not upgraded mine yet, but I'm planning on going to 4" straight. I've been told by several local exhaust shops that deleting the muffler won't provide any noticeable improvement since it's a high flow design, but getting rid of the cat will.

 

The biggest advantage to a complete 4" turbo back exhaust system will be EGT control. Let us know if we can help...

 

Here is mine. I like it, and it is my suggestion. Questions, feel free to ask.