Exhaust piping changes sizes...
 

My "friend" removed his cats and put it in a straight pipe (N/A). However, the possible issue being, the pipe is a different size than the ones it connects to (see pictures). Shown is the front (left side of first picture) and rear welds of the pipe, but the diameter is uniform throughout the pipe (which you can see almost all of).

Is this an issue?
Will it hurt performance?
Etc.

http://www.rotarycarclub.com/attachm...6&d=1206206556

http://www.rotarycarclub.com/attachm...7&d=1206206559

Another pic.

http://www.rotarycarclub.com/attachm...1&d=1206212595

I really don't think it would.

That's the problem with crush-bent or non-mandrel bent pipes...

Is it going to restrict flow?
Of course it is...

If it a restriction to power?
It depends...

If you run one size bigger, it should be okay.
Non-turbos run 2.5" as a rule-of-thumb, so if that's 3" crush-bent pipe, you should be okay.
If that's a 2.5" crush-bent pipe, then I'd say it's restricting power. :(


-Ted

Is it an issue going from a smaller pipe (stock downpipe) to a larger pipe (what the shop put in) to a smaller size again (stock area)?

It's not the best, but it shouldn't hurt.

Without going into a long discussion on expansion joints and gas flow turbulence, I wouldn't worry about it.


-Ted

:D Alright, thanks for the info. I'm not looking to squeeze all the hp out of the car I can, just making sure it's fun and reliable. Just wanted to make sure that the "bump" where it changes sizes wasn't causing a huge issue.

:icon_tup:

Ted has it right. If you were looking for some huge horsepower numbers and all of that, then yes it will do something. But I doubt you would be able to tell on the stock s4 n/a engine more than what your "friend" did by removing the cats.