V10 2005 F53 Chassis Motorhome.
 

I have increased my air intake system and factory filter to 4" and improved my power nicely. Now I am trying to understand why the right side of the exhaust Y pipe is restricted down for approx 2" before entering the Y pipe it is very choked before entering only on the right side. Reduced down by at least 1" for this 2" section very restrictive on purpose for some reason. Not sure it there is a reason? It has to create a lot of back pressure on this engine. Has anyone changed this out or is there an updated Y pipe for this engine. 2005 F53 chassis with a V10 20 valve engine.
Thanks for any help you can provide on this, David.