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This is a discussion on Can Ya Help A Brotha Out? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; i just bought a 2012 impreza wrx 5 door. im about to put a new exhaust system on it. but ...

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    Can Ya Help A Brotha Out?

    i just bought a 2012 impreza wrx 5 door. im about to put a new exhaust system on it. but is it better to put a 3" pipe or 2.5" inch pipe? someone told me i would lose HP if i got 3". Can Ya Help A Brotha Out?

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    Good news, everyone! xxxxxxxAnub1s's Avatar
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    What kind of exhaust system? Axelback, catback, turboback? Replacing the entire turbo-back section requires tuning, catback and axelback are just noise makers. If you're not replacing the downpipe, the diameter doesn't matter much at all, so go with whatever you like best and fits your budget.

    Whoever told you that 3" piping decreases HP output doesn't know much about turbocharged cars, I'll say that much.
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    Registered User fridaythe13th's Avatar
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    more air-flow = more hp. It sounds like you are just getting a catback, so you should pick up about 8-10 hp from that... If you are looking at anything less than a catback don't waste your money. Get a manual boost control and a flash instead for bigger gains.

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    Re: Can Ya Help A Brotha Out?

    Quote Originally Posted by Anub1s View Post
    What kind of exhaust system? Axelback, catback, turboback? Replacing the entire turbo-back section requires tuning, catback and axelback are just noise makers. If you're not replacing the downpipe, the diameter doesn't matter much at all, so go with whatever you like best and fits your budget.

    Whoever told you that 3" piping decreases HP output doesn't know much about turbocharged cars, I'll say that much.
    This ^

    Quote Originally Posted by fridaythe13th View Post
    more air-flow = more hp. It sounds like you are just getting a catback, so you should pick up about 8-10 hp from that... If you are looking at anything less than a catback don't waste your money. Get a manual boost control and a flash instead for bigger gains.
    Yea wut?? :what:

    Where do you get 8-10 hp from?...

    What's wrong with an axelback? A catback gives you no hp, just noise, which can be achieved by just an axelback.

    Where on earth did you get the mod path of mbc and tune as first mods????


    OP, please don't listen to this guy ^



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    Can Ya Help A Brotha Out?

    Quote Originally Posted by fridaythe13th View Post
    more air-flow = more hp. It sounds like you are just getting a catback, so you should pick up about 8-10 hp from that... If you are looking at anything less than a catback don't waste your money. Get a manual boost control and a flash instead for bigger gains.
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    Registered User Gendax's Avatar
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    Quote Originally Posted by Anub1s View Post
    If you're not replacing the downpipe, the diameter doesn't matter much at all, so go with whatever you like best and fits your budget.
    Yeah, mix and match on exhaust diameter sizes without changing anything doesn't really get you any gains. If all you had to do it make it bigger for "more air-flow" we'd all be rocking 6" diameter.

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    Registered User fridaythe13th's Avatar
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    easy there NX ha. basic mods where I come from are a turbo back, MBC and a tune

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    Registered User xFalleNx's Avatar
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    friday13th, don't take this as rude or anything personal, but these are so completely different cars than what you come from. Take some time and read up on what mods to do, and how these cars like to be modded (as odd as that sounds lol). With Subarus there's a right and very wrong way to do things.
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    Registered User fridaythe13th's Avatar
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    oh yea dude no offense taken... I was actually just reading up on COBB's website and it looks like a turboback and a tune is what they recommend as well. It looks like the AccessPort for you guys takes care of the boost control from what I can tell. I was just thinking most aftermarket exhausts/ downpipes are 3 inch anyway, so if the OP had any real intentions of gaining HP a 2.5 inch or axelback would probably not be the best way to start modding.

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    Registered User InsaneManiac's Avatar
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    Adding any type of exhaust post the axle or cat will only create the boxer rumble. Screwing with anything beyond the cat, including the Up Pipe or down pipe will require the ecu to be tuned. The problem is that adding a bigger exhaust does not make it increase horsepower, only when removing the cats or getting a high flow turboback does the horsepower increase considerably. The Subi is still contrained due to the cats.

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    He simply abides. SD_GR's Avatar
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    An up pipe does not require a tune.

    Inscreased exhaust Φ will not reduce output or torque.

    A different exhaust will only require a tune on newer cars.

    A catback or axleback will not increase output.

    The fastest Subarus ever made, the cars that made Subaru famous, all had catalytic converters.

    EDIT: When I say Φ above I really mean ⌀, but I don't know from keyboards, sorry.
    Last edited by SD_GR; 09-21-2012 at 01:47 PM.
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    Okay thanks a lot guys. ya i was talking about a borla catback exhaust (I saw a 2.5" and a 3" downpipe and was wondering what one would be better). What would the optimal set up be for power increases?

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    Master Baiter EJ257's Avatar
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    Quote Originally Posted by noobguy
    Okay thanks a lot guys. ya i was talking about a borla catback exhaust (I saw a 2.5" and a 3" downpipe and was wondering what one would be better). What would the optimal set up be for power increases?
    The only 2.5" downpipe I know of is Cobb, and that tapers at the downpipe/catback joint. Honestly, until you modify your car to the point where buying a new downpipe doesn't matter, don't worry about it. Instead, worry more about what the catback you intend to buy is setup for; if it's setup for a 2.5" donut flange, buy a 2.5" downpipe (or buy a 2.5"/3" adapter); otherwise, buy a 3".
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