Catless Downpipe
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This is a discussion on Catless Downpipe within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; So I have a 2007 Wrx. I have a Cobb accessport with the 91 Octane map that came with it. ...

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    Catless Downpipe

    So I have a 2007 Wrx. I have a Cobb accessport with the 91 Octane map that came with it. Also a Magnaflow axle back muffler, don't think the muffler changes anything.

    Anyways I recently found a really good deal for a Catless Invidia downpipe brand new. I really want it because it's about half price as it normally would be.

    So my question is can I do it without over boost issues. The guy at the store that's selling it said that it was fine because I have the Cobb AP with the Cobb Maps on it.

    I always thought you needed a Protune to get away with a catless downpipe. Also the Emissions don't matter to me because I live in an area where they do not do emission testing.

    Let me know what you guys think.

    Thanks

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    lit fam XJman's Avatar
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    You could but it's going to need more than a Cobb AP from my knowledge. The guy at the store sees green. He will tell you what you want to hear to sell a product.

    I'm catless, it sucks. The smell, the endless cleaning of the tips, black soot on the back of the car. Buy catted

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    STinfection WRX-maniac's Avatar
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    Can you run a catless downpipe on the cobb stage 2 map? Technically yes. But the map notes do recommend a catted downpipe. There is no way a tune can or will eliminate boost creep. It's also not guaranteed that you develop boost creep with a catless. It's about a 50/50 shot.

    Most people buy catted downpipes for the peace of mind that they drastically decrease the chances of boost creep. So you may be able to run a catless downpipe with no issues. BUT, if boost creep does occur, no tune, whether it be a protune, e-tune, or base map from an accessport, can get rid of it.

    The only way to get rid of boost creep once it starts is an external wastegate setup. If you plan on going to an ewg eventually its not that big of deal, if you don't then you will have to spend a penny or two on the parts needed. Which are the following: uppipe for ewg, wastegate, gaskets, protune. So anywhere from 1k to 1.5k in parts and tune if you do the labor yourself.
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    Master Baiter EJ257's Avatar
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    GD 2.5L TD04s ('06/'07) weren't really prone to boost creep like other models were.

    For what it's worth...Cobb used to sell catless and catted versions of their downpipe for that car for years, and didn't have the "high-flow catalyst" stipulation in their mapping for those years. They ceased sale of catless downpipes a few years back, and once they only sold catted units, that stipulation found itself in those map notes.

    I don't have the issues with catless cars that I've tuned like XJ talks about. There are minor increases in certain things, but he makes it seem night/day; instead of level 8-9 with a HFC unit, you're at 10.

    If you don't have to deal with emissions, have a line on an inexpensive catless Invidia pipe, go for it. Worst case, sell it and be out the hour install time and the $20 turbo/downpipe gasket you'll need to replace when you find a catted unit.

    Quote Originally Posted by WRX-maniac
    The only way to get rid of boost creep once it starts is an external wastegate setup. If you plan on going to an ewg eventually its not that big of deal, if you don't then you will have to spend a penny or two on the parts needed. Which are the following: uppipe for ewg, wastegate, gaskets, protune. So anywhere from 1k to 1.5k in parts and tune if you do the labor yourself.
    You need to increase flow out of the wastegate; this is done either by going external or porting the factory one. If you're not sure about what you're doing, you should NOT try to DIY a wastegate port job; you can irreversibly ruin the turbo if you don't port it properly.
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    Quote Originally Posted by EJ257 View Post
    GD 2.5L TD04s ('06/'07) weren't really prone to boost creep like other models were.

    For what it's worth...Cobb used to sell catless and catted versions of their downpipe for that car for years, and didn't have the "high-flow catalyst" stipulation in their mapping for those years. They ceased sale of catless downpipes a few years back, and once they only sold catted units, that stipulation found itself in those map notes.

    I don't have the issues with catless cars that I've tuned like XJ talks about. There are minor increases in certain things, but he makes it seem night/day; instead of level 8-9 with a HFC unit, you're at 10.

    If you don't have to deal with emissions, have a line on an inexpensive catless Invidia pipe, go for it. Worst case, sell it and be out the hour install time and the $20 turbo/downpipe gasket you'll need to replace when you find a catted unit.



    You need to increase flow out of the wastegate; this is done either by going external or porting the factory one. If you're not sure about what you're doing, you should NOT try to DIY a wastegate port job; you can irreversibly ruin the turbo if you don't port it properly.
    I like where you're going with this, I'm very tempted to go and pick up the downpipe tomorrow haha. But The only thing is if I were to expierence boost creep, could it hurt my car and I heard that it puts the car into limp mode but you can just clear the code with an OBD reader and you're good until it comes on again.

    Also if I were to get this Catless downpipe would it be the best Idea to put the OTS stage 2 tune the cobb has?

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    lit fam XJman's Avatar
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    It can kick it into limp mode, and it's not really good for your car.

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    Quote Originally Posted by Robbie7c
    I like where you're going with this, I'm very tempted to go and pick up the downpipe tomorrow haha. But The only thing is if I were to expierence boost creep, could it hurt my car and I heard that it puts the car into limp mode but you can just clear the code with an OBD reader and you're good until it comes on again.

    Also if I were to get this Catless downpipe would it be the best Idea to put the OTS stage 2 tune the cobb has?
    You'll either hit fuel-cut and/or trigger an wastegate solenoid (P0244) diagnostic troubleshoot code if your ECU is reading boost above a certain threshold (programmed into the calibration); in the case of a DTC, the CEL will flash, the cruise control will be disabled, until it clears itself or you clear it (any AutoZone, Pep Boys, etc. can lend you a OBDII code reader that can do this for you).

    Whether this is the result of an overboost (where running one of the alternate wastegate maps will help) or boost creep (the wastegate simply can't bypass enough air) would have to be determined via datalogs. I would start with the base maps that Cobb provides, and when you're relatively happy with the power level, going to a good shop and getting a custom calibration done on your car. This is obviously assuming datalogs of the base map come back clean (if not, you'll need to either fix something mechanical or in the software).

    The custom calibration will make drivability better, and will give you additional power everywhere in the RPM band. At $400-500 / session, you don't want to be paying for this too much, so make sure you're pretty content with where you're at before dropping that kind of coin. If you don't think that the power is enough, it may be worthwhile to wait on the custom calibration until you pick up additional supporting mods for a turbo swap. VF-series takeoff turbos from the STI are pretty common swaps, but you will be injector limited with any larger turbo, so keep that in mind. I wouldn't want to spend $400-500 to get a custom tune, then decide a few months later that you need more power, and be out that money.
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    Okay, Thanks for all the info guys, I think I'm gonna stick with a catted pipe to save the headache if I am unlucky enough to experience boost creep. Plus I don't plan on doing anything insane with my car until I can afford a 2nd vehicle. Just want a quick daily driver for now. Anyways I really appreciate the help!

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    So what you'r guys telling me that no tune even the ecutech can tune catless downpipe.where i'm living all of the subarus with catless downpipe and didn't hear about any problem.
    Exactly what is creep boost,i can't translate it very well.
    Thanks.
    By the way i'm with 2008 old shape forester xt.

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  12. #10
    lit fam XJman's Avatar
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    It's a mechanical limitation with the wastegate size as far as I know. So software can't fix that.

    Overboosting is when the vehicle makes more pressure than its supposed to at any given point. Enough of it and you can lean out and go bang, or in an absurdly extreme case lift a head.

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