I currently have a 2005 Subaru Impreza RS with a cat back magnaflow exhaust system running 2.25 in piping. Im seriously thinking about trading it in for a TC. If i do, i want to put the same system on the TC (magnaflow catback). My question is should i use 2.25 again or 2.5 in piping? I want to gain as much power as possable throughout the entire RPM AND keep my low end torque. Thanks in advance.

 

There is an exhaust system coming out by Magnaflow using 2.25" piping, the same size as stock. There are about 2 - 3 others coming out using 2.5" piping. However, we dont have dynos for the various exhaust, so, we cant really say which size will be optimal for a N/A 2AZ-FE. Magnaflow claims that 2.25" will be optimal, others such as Draxas say 2.5" will be best. We'll soon see. Sorry I cant be of further help. But, one thing we do know for sure is that the factory s-pipe seems to be very restrictive, squeezing down to less than 2" in some parts, so replacing it will be crucial for optimal exhaust flow no matter the size of the piping. The Draxas and Creative Compact exhaust systems will include a replacement s-pipe. Magnaflow hasn't announced a replacement s-pipe as of yet (as far as I know).

 

Ok thanks man. Ya i can get a full magnaflow cat back system from Dual Tone by my house for $318.00. From what ive seen its a great deal. Some people are paying more than that for an axle back!

 

You're welcome. Yeah, there are some pretty expensive axle-backs out there. And the full cat-back systems are going for around $680, but they include the replacement s-pipe. But, Draxas will be offering their s-pipe separately for around $150. So, you could get your complete system for about $470! I'd say that's a darn good deal indeed. :D

 

the difference in the 2.5 and 2.25 isnt much, it just makes more power in different areas, it really depends on what you are looking for.

[idential cars, with the exception of the exhaust system.]
car1: 2.25inch exhaust, makes more power in the low-mid range
car2: 2.5inch exhaust, makes more power in the top end

it really depends on your type of driving.