What is the difference between dual and single outlet exhausts?

GD STi's come with a single outlet exhaust. GR STi's come with a dual outlet exhaust. Why is there this difference and why do some GR owners still put on a single outlet exhaust on their GR's?

I've done some reading up on that very question myself, after seeing several 08+'s sporting single pipes. Everything I've read is that if there is a difference in performance, it's negligible at best until you hit 350+ hp. Maybe Fuji or one of the tech heads can correct me if I read wrong..

The stock exhaust lay out is super inefficient and can create back pressure if you are not using a large enough diameter piping. You have to look at how it curls up and around and over stuff. The ideal exhaust is a straight back pipe with as few bends and curves in it as possible. Most after market systems follow the factory piping just with a larger diameter. Where as the single cans tend to be a much better line back with fewer curves or bends. For instance my N1 only has 2 bends total in all the piping, compared to my Borla with looped over its self and then twisted around into a huge muffler.

Also I personally like the single exhaust exits better. I think it is a bit presumptuous to have a quad exhaust on a 4 banger. A corvette or BMW M3 or M5? sure why not. But a Japanese econ box turned rally car? No.... Plus I have always wanted a huge single fart can out the back of the car. Then again I am ricer at heart. I have stickers and a load of other ricer items.....

Ok here is my next question. What is more effecient: single tbe outlet or dual tbe outlet?

What do you mean...ike for a single exit, one or two pipes? If so, mostly looks. Depending on specific diameters, one might be sligtly less restrictive than the other.

I forgot to mention one keyword haha. Straightpiped tbe single or dual. Any difference?

A straight pipe will always be best for power and flow. AMR did a quick test on a stage two gr where they compared the stock catback to a open downpipe (very similar to properly sized straight pipes). There was a 15whp differance compared from before and after. More importantly than straight pipes or the number of exits is the diameter of the piping. For a non E85 stock turbo build the stock catback will not be a limting factor (at least from what i have seen via dyno plots online) but once you got e85 or larger turbo it would be advisable to go to a true 3inch all the way back. Remember a system can only flow as much as the smallest point allows. A large number of after market cat backs have a 2.5 inch neck down to meet up with the stock dp.