simple answer No and no.
The exhaust is different than a wrx (flange at the cat is in a different location), and 3 inch piping is completely over the top. If you're only in this for the sound get an axleback made at an exhaust shop or get a cat back, 2.5 inch is about as big as you should go. But it's not going to make more power.

Edit: Additional info, think about how water flows in a pipe (air works similarly). To big a pipe and flow slows down despite volume, to small and the speed increases but volume goes down. To big of piping slows the velocity of air leaving the engine which creates less vacuum pulling air into the compression chamber when both valves are open. To small and air can't move out fast enough. However you're just considering a cat back so the headers and cat will remain unchanged so piping size post cat/headers is not as important. Regardless three inches is totally excessive.

 

word

 

I try to be as helpful as I can instead of just a "no"

 

You could probably have that one modified by a local shop to fit if you wanted. I would go on youtube and look up different exhaust to judge sounds and see what you like. There are very nice options specific for the non turbo subarus. Check out stromung, they make a fabulous product.

 

What size pipe is the stock system? Is it 2"

 

Stock is 2.25.

 

Stock is 1.75 up to 05. It is supposedly 2.25 after 06.

You will notice less low end punch with bigger exhausts. Mids improve.

 

Leaving the down pipe, y pipe, and (forester) cat stock, than going to 2.5" right after the cat with a WRX muffler, what are the pros and cons?

I met the guy who has from an 06 WRX Impreza the section that has a free flow cat and a larger muffler. He looked at mine and thinks it would definitely fit. He would be willing to install it with me to make sure it does indeed fit. He wants $100 bucks for both. So here is how it would be laid out: Stock Down pipe -to- stock y-pipe -to- stock cat -to- WRX free flow cat section -to- WRX muffler. The pieces I would be adding would be 2.5'' pipe.

 

^
oops, thanks for the correction!

 

Pros:
Looks better for sure hahaha no more dinky little tube in the back
Smoother power delivery (IMO)
Slightly better mid response (Got up to 70 mph a bit easier for me)
Slightly lower tone (no more sewing machine noise :lol

Cons:
2.5" may or may not be too large. Losing that back pressure means losing power. 2.5L engine might be able to handle it though. But if it's a OEM WRX catback, it goes down to 2.25" so no worries.

And you don't have a downpipe because you're not a turbo. The turbo cat is angled differently. You can try get it custom fitted by rotating flanges, but it's too much work IMO. Plus your O2 sensor will need to be relocated.

The only useful stuff to you is the midpipe and the axle back. Then you'll either need to cut, rotate, and extend the midpipe female donut flange (that meets the stock cat) about 2", or get a custom adapter made that fills that gap and provides you with the two angles the two flanges need.

 

Easy mods

Neoshi,

I was not sure what you meant by the doughnut but now I know what you mean. It would take some interesting exhaust work to make it line up right. Is there a complete kit that comes with all of the exhaust parts for a n/a subaru. I essentially was looking to get a little rumble and a bit more fun out of the car for cheap cheap cheap.

On the cheap what are some easy mods that will result in fun?

 

Well, the cheapest path is an OEM exhaust like the WRX exhaust, with modified midpipe flange (the one that connects to the stock cat), and maybe a set of borla replica headers from ebay.

Alternatives are the OBX catback (OBX Catback Exhaust 98-05 Subaru Impreza 2.5RS 2.5L NEW: eBay Motors (item 190430899946 end time Sep-12-10 14:40:33 PDT) N1 catback (02 04 05 Subaru Impreza 2.5RS 2.5 RS N1 Catback Exhaust: eBay Motors (item 390220437178 end time Sep-19-10 01:15:03 PDT)) off of ebay.

The ebay ones are a good option if you can only find a OEM exhaust for $150 or more and can't do the modification yourself (requires cutting, spare 2.25" pipe, and welding). However, the ebay ones are louder than any modified OEM option. Match one of these ebay CBEs with a borla replica header and you're good to go. You will need to make some adjustments to these ebay CBEs though, namely for the hangers, but that can be easily done with a small sledge or by heating and bending to fit forester positions.

Rough costs:
OEM CBE: $100 or less, sometimes free
Modification to OEM CBE: $100 at an exhaust shop, less if DIY or connection
OBX CBE: $325, bolts up but need to adjust for hangers (cobb replica)
N1 CBE: $280, bolts up but need to adjust for hangers (looks like a potato cannon)
Borla UEL replicas: $150

 

Took the plunge

I bought a 06 WRX muffler with a midpipe that has a high flow cat attached to it (BTW it is 2.25"). I thought it would work, but like you said, you need to have the flange rotated. It is also about 3 inches to short.

2 questions:

1. can I drive the car without the midpipe or muffler? (it is loud)

2. What is the best way to get it to mate up? Is there a transition piece you can buy?

 

You can... but it'll get really dirty down there from the soot. You may also have problems with any nearby components being pounded by the heat of the exhaust. The cabin will also stink from the fumes.

You can ask an exhaust shop to make you something like this:
For those wanting to run GD catback on a GC - Subaru Impreza GC8 & RS Forum & Community: RS25.com

I'm having one made that utilizes two donut flanges (to emulate stock). The manufacturer just receive the necessary parts to finish R&D but I have no ETA.

 

That's Perfect! I will take some pics of the install and post my results in a week or so.

 

Take it to a shop and they can make one up, it shouldn't cost much.

 

Pictures of Finished Install!!!!

I took the exhaust from the 06 WRX and had my exhaust shop fit it up for me. It sure was loud driving it there with no muffler! After the install I don't really hear any difference, a little disappointing. I will run through a few tanks of gas and see if it help any with fuel mileage.

Total costs:

06 WRX stock exhaust 2.25": $100 off Craigslist
Install by Exhaust shop: $75
Rear Muffler Gasket from Stealer: $15

TOTAL: $190.00

Was it worth it? We will see.

Next project, CAI!!!

 

Will WRX 3inch aftermarket exhaust fit Forester XT 05? Does it need any modification?

 

Not sure entirely, but most likely going to need to mod like the pics above.

 

Will a '11 WRX or even '15 STOCK OEM Catback Exhaust, mid pipe and Y pipe fit a Forester N/A 2010 is my question?

Looks the same too me, as far as hangers and stuff, but IDK...

Please help. As I need my Y PIPE REPLACED asap.