So, I've been looking at posts on exhausts, and the only thing I can figure is that most exhuast are equall, so it just depends on who you want to give your money to, and some actualy decrees your HP. My question comes as what is the ideal diameter of the pipes? At what size do they alow gasses to escape the best with out losing that much needed back pressure? I've seen mainly 63 mm and 70mm exhuasts out there and was wondering which aplication is preferable for someone not planning on going forced air induction. I realy don't care about sound or noise level, so it's all about gains. I read on one web page that the 70 mm was the idal for hp gains, but then why sell a 63mm?

 

single pipe 70mm are proven to give the most bhp gains.

best imo is t1r