I was wondering what you guys thought about a four-to-two header on an inline 4cylinder engine (like a civic, integra or rsx) with two full exhausts sytem

 

Why would you need two full exhaust systems on a I4 engine? The exhaust would loose flow, stagnate, and then cause you to lose a lot of low end power. A single exhaust from a reputable aftermarket company will give you better gains and will be a whole lot easier to install.