This is a discussion on Upgrade opinions within the New Member Hangout forums, part of the Community - Meet other Enthusiasts category; Originally Posted by Calvinball Sort of. It's a term that doesn't really apply to modern Subarus, or many other modern ...
You can use the same 91 octane you re using, it will simply be less efficient. If you have the option to use alternative fuels, they generally yield more impressive results for less overall $ invested into upgrades to the car.
A straight pipe is generally illegal, harder to tune for, is considered rude by the general public, and is likely to cause you more hassles than pleasures. You can also get a very free flowing road legal exhaust system for not much more $.
A turbocharged car benefits from a free flowing exhaust. A header, up pipe, down-pipe, midpipe, and axle-back muffler section can all be bought together or separately, I recommend a complete system. Invidia, as mentioned, is excellent. There are no concerns for installation, though I would purchase 3 layer stainless gaskets from Subaru's 'SPT' parts catalog for each part of the system you upgrade. These last and do not leak.
Invidia will include a 'waffle' style gasket set, which IMO is not up to the rigours of regular driving of a car being upgraded as an exhaust system like this one implies.
There are other companies making equivalent systems. It would be a good idea to do as the previous posts instruct, read as much as you can. If you get a chance to speak with other Impreza owners, ask about their systems.