Has anyone tried dual exhaust on a ej22 or any other subaru flat four for that matter? I would think this would improve performance. Obviously running the two exhaust pipes out the back would present issues.

It won't do anything for you.

I second 777's motion.

 

 

Two silencers might give something in terms of looks, for some people. If you mean running two entirely separate systems from each head, then you will likely suffer power loss across the rev range. MAYBE, you would gain a tiny amount of power at max revs. Maybe.