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  1. #1
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    Catted Dp/Catless Dp with stock catback.

    Hey Guys,


    I am planning to get a AR catted DP for my N54. I would like to find out how restrictive is the stock catback. I know there's a second cat inside the pipe. I want to keep the stock catback to keep the noise level down. But if that is the big factor to affect over all performance than I might get the Maddad catback as well. Any Logs to show the difference? Thanks.:party0030:

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    Its restrictive enough.....You can do highflow Catted DPs and have your seconday catts in the midpipes removed or upgrade your midpipes all together with no secondary catts. This way you dont have to worry about the CEL with cattless DPs, drones, rasp or bad smells with the help of a good axle back exhaust

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    Click here to enlarge Originally Posted by Sam0329 Click here to enlarge
    Hey Guys,


    I am planning to get a AR catted DP for my N54. I would like to find out how restrictive is the stock catback. I know there's a second cat inside the pipe. I want to keep the stock catback to keep the noise level down. But if that is the big factor to affect over all performance than I might get the Maddad catback as well. Any Logs to show the difference? Thanks.:party0030:
    Are you a 135i? Dont go catted downpipes, go resonated if anything.

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    Yes 135. Reason for catted DP is I dont want the smell. Used to own a GT3076 STI and no cat at all. I can smell everything lol.
    So AR Catted DP, Maddad mid and stock Axle back?

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    Sorry, i dont know enough about the stock 135i exhaust system, but i would really urge you to resist getting catted downpipes. Its a waste of money in my opinion. If you can put high flow cats in your midpipes id say that is the way to go, and should be MUCH less expensive.

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    I have catless downpipes on my 135i mated with the stock catback which still retains the secondary cats in place. I honestly do not smell anything with this setup and I am coming from a fully catless Evo with an open o2 dump. There is no drone or raspiness associated with this setup either which sounds like stock until you go WOT, and then it sounds more 'throatier' which is honestly an improvement IMO.

    The 135i catback is more restrictive than the 335i catback, but the gains are mostly from removing the primary cats in the downpipes itself. IMO I would get catless downpipes and retain your OEM catback for the most gains while still retaining close to stock like sound. If you get a tune (which you should get no matter what), you won't have to worry about the check engine light.

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    Thanks, I am just wondering how restrictive is the second cat inside the catback.

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    I am running Active Autowerke's catless downpipes, with a stock cat back system. Dynos have shown that this setup vs a full catback system has no difference in power. For the smell, and to get an overall better, cleaner burn, I run 30% E85, which eliminated the smell.

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    I don't know how restrictive the secondary cats are in the 135, but in the 335 they are not restrictive at all from what I can tell. Many of the record holding cars run stock catbacks.
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    1 out of 1 members liked this post. Yes Reputation No
    Thanks guys

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    So I got replied from Cobb. There is around 15 HP difference between stock catback and after market with catless DP Click here to enlarge

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    Going with the AR Design catless downpipe is going to yield the best gains. It's also cheaper than going with the catted option. Keeping your stock secondaries in place will help cover the smell and that is the route that I'd recommend for you to go with as well!
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    Click here to enlarge Originally Posted by Sam0329 Click here to enlarge
    So I got replied from Cobb. There is around 15 HP difference between stock catback and after market with catless DP Click here to enlarge
    Not surprised, the 335 catback is fairly free flowing while the 135 is much more restrictive. If you look at COBB's Map Notes, the 135 specifically has "Suggested Upgrade" for the catback on every map (from Stage 1 to FBO Stage 2+FMIC).

    The OTS E30/Race Maps suggest an aftermarket exhaust for both the 135 & 335
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    Click here to enlarge Originally Posted by Turkeybaster115 Click here to enlarge
    I am running Active Autowerke's catless downpipes, with a stock cat back system. Dynos have shown that this setup vs a full catback system has no difference in power. For the smell, and to get an overall better, cleaner burn, I run 30% E85, which eliminated the smell.
    Do you have these dynos?
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    Click here to enlarge Originally Posted by RnmEvo9 Click here to enlarge
    I have catless downpipes on my 135i mated with the stock catback which still retains the secondary cats in place. I honestly do not smell anything with this setup and I am coming from a fully catless Evo with an open o2 dump. There is no drone or raspiness associated with this setup either which sounds like stock until you go WOT, and then it sounds more 'throatier' which is honestly an improvement IMO.

    The 135i catback is more restrictive than the 335i catback, but the gains are mostly from removing the primary cats in the downpipes itself. IMO I would get catless downpipes and retain your OEM catback for the most gains while still retaining close to stock like sound. If you get a tune (which you should get no matter what), you won't have to worry about the check engine light.
    THIS

    my 135i also had the stock exhaust with AR 3" downpipes. best happy medium of performance, sound, smell, etc. highly recommended for 135i. also, don't forget to zip tie your exhaust flap actuator line

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Do you have these dynos?
    It's from a guy on E90crap.com who ended up getting banned. Click here to enlarge Click here to enlarge

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    Click here to enlarge Originally Posted by Turkeybaster115 Click here to enlarge
    Picked up a little peak torque but ya a rear section isn't going to do all that much.
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    Thanks for the dyne graph. It doesnt looks like its as restrictive as cobb 's claim... interesting. I guess I am keeping the stock catback Click here to enlarge

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    Click here to enlarge Originally Posted by Sam0329 Click here to enlarge
    Thanks for the dyne graph. It doesnt looks like its as restrictive as cobb 's claim... interesting. I guess I am keeping the stock catback Click here to enlarge
    That's a 335 not 135

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    Oh yes...

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    1 out of 1 members liked this post. Yes Reputation No
    So just pull the trigger and ordered the Maddad street series exhaust. Will do some logs with stock catback and Maddad Click here to enlarge

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    Click here to enlarge Originally Posted by Sam0329 Click here to enlarge
    So just pull the trigger and ordered the Maddad street series exhaust. Will do some logs with stock catback and Maddad Click here to enlarge
    Haven't heard of this exhaust. Interested in seeing what you think.
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  23. #23
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    Oh sorry. I meant to say MadDad Whisper EuroSport 135i.

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    I still think that if you are getting it for power instead of looks or sound, it will disappoint you.

  25. #25
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    I had Agency power exhaust on my 135i and had it on and off, I never noticed a big difference in power while taking it on and off... but what i ended up doing is keeping the midpipe because it deleted the secondary cats and using the stock muffler...

    I would just get catless DP and keep stock catback if you were going to do one thing for power only.

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