devilmademedoit Posted June 23, 2011 Share Posted June 23, 2011 I have a 98' legacy wagon in need of new exhaust system. Right now I want to run from rear cat back. I cant seem to find any kits for this car so I plan to fab one up. I was planning on a magnaflow universal high flow cat. The stock diameter seems small maybe 1 3/4"? What is a good size to increase this to? It has the 2.5l in it. As of right now I plan on no motor work besides maybe building some sort of cold air intake and a header. Can I blow it out to 2 1/4- 2 1/2"? or would I lose too much back pressure? I am new to foreign engines I know that when building v8 engines if you dont produce enough HP for the exhaust, you actually lose performance. For muffler I was planning on some big 4" outlet can to make it sound a bit loud Link to comment Share on other sites More sharing options...
Zues Marine Posted June 23, 2011 Share Posted June 23, 2011 since your exhaust flows only as well as your smallest point, i'd start with the headers, speedyracer.com has 2.5L headers for the 2000-2004 Legacys ($140) that bolt right up to your wagon, with that. i'd also recommend heat wrapping those headers, with the thinner walls you will no doubt hear some ticking from the valves, no one else may be able to notice, but you will, and itll drive you nuts.. as for the cat, any HFC will more likely tthan not give you a p0420 code due to the increased flow and your rear o2 sensor will be freaking out, there is a 'spacer' method' that many people have used for the rear o2 that safely eliminates that code from the cat.. the highest diameter you want for the most mpg and fuel economy is 2.25", anything higher without other engine mods such as cams will cause you to lose too much back pressure, i highly recommend not adding a retarded WRX sized watermelon shooter and looking like a tool, you can get plenty of sound from other mufflers and be way more respected by other auto enthusiasts here is my setup: Speedyracer headers - heatwrapped stock cats Vibrant performance muffler #1046 2.5" mandrel bent cat back exhaust piping 18" resonator [ame=http://www.youtube.com/watch?v=4WHAruAI3PA]YouTube - Subaru Legacy Full 2.5" Exhaust[/ame] [ame=http://www.youtube.com/watch?v=JOTYTo8nKaE]YouTube - Subaru Legacy Vibrant Performance Exhaust Clip[/ame] Link to comment Share on other sites More sharing options...
grovlet Posted June 28, 2011 Share Posted June 28, 2011 [ame=http://www.facebook.com/video/video.php?v=209477195756646&comments]My Custom Exhaust:[/ame] - Speedy Racer Header - Wrapped in DEI Titanium Wrap - High Flow Cat - Dynomax Muffler - 2.25" Piping Link to comment Share on other sites More sharing options...
devilmademedoit Posted June 29, 2011 Author Share Posted June 29, 2011 Thanks guys Im going to order some 2.25" pipe from summit this week and start screwing around Link to comment Share on other sites More sharing options...
devilmademedoit Posted August 7, 2011 Author Share Posted August 7, 2011 Ok I'm finally ready to do the new exhaust. Will this header fit on my 98' legacy gt wagon with the ej25? http://www.speedyracer.com/servlet/the-173/Subaru-Impreza-Header-for/Detail Also I'm going to get a new replacement cat. The first one with the o2 sensors in it. What would happen if I eliminated the second cat? What is the reason behind the second one anyway? Link to comment Share on other sites More sharing options...
devilmademedoit Posted August 8, 2011 Author Share Posted August 8, 2011 No info on cat? Link to comment Share on other sites More sharing options...
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