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  1. #1
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    1 out of 1 members liked this post. Reputation: Yes | No

    Lets talk about exhausts.

    Ok guys.

    I have a straight exhaust with a x pipe. No cats and nothing.
    I have been talking to a friend and he sais that I would be getting some more power if I would put Magnaflow cats and I would get rod of the drone sound.
    Is that true? Also the fuel smell wouldnt be as strong.

    Here is a vid of how it is running.


  2. #2
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    The fuel smell is due to the cats, so yes, it would help if you put cats in.

    I don't buy that you would gain any power, you would lose it IMO.

    The drone on the other hand, that you would likely get rid of.

    I'm surprised it doesn't even sound that loud in the video, nice ride man.

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    I have been told this:

    The [COLOR=blue !important][COLOR=blue ! important]engine[/COLOR][/COLOR] itself needs backpressure to maintain it's compression ratio. Any modification to the exhaust will cause loss of power as proven by my dynos. __________________

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    Click here to enlarge Originally Posted by Fatandre Click here to enlarge
    I have been told this:

    The [COLOR=blue !important][COLOR=blue ! important]engine[/COLOR][/COLOR] itself needs backpressure to maintain it's compression ratio. Any modification to the exhaust will cause loss of power as proven by my dynos. __________________
    Yep, by whom?

    The backpressure stuff is just a myth IMO. I gained power ditching the cats, everyone does.

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    Thats what I have been hearing on some other forums.

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    Click here to enlarge Originally Posted by Fatandre Click here to enlarge
    Thats what I have been hearing on some other forums.
    Easy way to prove it would be to get a baseline dyno and then get cats and redyno.

    You won't beat your straight pipes for power. You should be looking into a tune!

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    or schrick cams first?

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    We did a E39 540i (M62TUB44) straight pipes (car had o2 sensors prior to cats and after cats)...

    car did a respectable 304hp without the cats, but drone was a issue, as well as check engine light during idle...

    installed WALKER RACE-CATS, 311hp (a gain of 7hp) and no more check engine (service engine soon in US) light Click here to enlarge

    HOWEVER... M70 and M62 may of course differ Click here to enlarge

  9. #9
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    Click here to enlarge Originally Posted by Fatandre Click here to enlarge
    or schrick cams first?
    Well, if you want to spend money for the cams and then tune, by all means. You are going to need a tune one way or another.

  10. #10
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    Click here to enlarge Originally Posted by angelic0- Click here to enlarge
    We did a E39 540i (M62TUB44) straight pipes (car had o2 sensors prior to cats and after cats)...

    car did a respectable 304hp without the cats, but drone was a issue, as well as check engine light during idle...

    installed WALKER RACE-CATS, 311hp (a gain of 7hp) and no more check engine (service engine soon in US) light Click here to enlarge

    HOWEVER... M70 and M62 may of course differ Click here to enlarge
    Who is we and where are the dyno results?

    I gained a considerable amount of power ditching cats on my M3. As does everyone else who ditches cats. If cats made power, we wouldn't mess with the factory exhaust as it gives a ton of back pressure.

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Who is we and where are the dyno results?

    I gained a considerable amount of power ditching cats on my M3. As does everyone else who ditches cats. If cats made power, we wouldn't mess with the factory exhaust as it gives a ton of back pressure.
    We... is me and a friend of mine..

    I don't know if it had anything to do with the fact that a M62TUB44 has 4 oxygen sensors in the exhaust, pre-cat and post-cat...

    But my suspicion lies there, both dyno runs were made in the same day with about 40 minute interval on the same dyno...

    I'm actually leaning towards that theory rather than backpressure, so as i stated before. I'm not familiar enough with the M70 exhaust techniques Click here to enlarge

  12. #12
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    Click here to enlarge Originally Posted by angelic0- Click here to enlarge
    We... is me and a friend of mine..
    Ah, gotcha, thought you might be referring to a company.

    Click here to enlarge Originally Posted by angelic0- Click here to enlarge
    I don't know if it had anything to do with the fact that a M62TUB44 has 4 oxygen sensors in the exhaust, pre-cat and post-cat...

    But my suspicion lies there, both dyno runs were made in the same day with about 40 minute interval on the same dyno...
    It's possible the 40 minute cool down was too soon and the car didn't adapt. You said it went from no cats to having cats, right?

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    1 out of 1 members liked this post. Reputation: Yes | No
    This is how it went down...

    OBD-II - read codes, had codes saying that values on post-cats were too high/low levels (don't remember which it was)

    Ran on dyno... 304hp 433nm

    Exhaust shop, install cats...

    OBD-II - clear all codes...

    drive around 15minutes...

    OBD-II - read codes, now clear of all codes, only some code about auxilary fan engagement something, not relevant so it was discarded...

    Ran on dyno... 311hp 435nm

    the torque numbers might be switched... i recall that it was an increase in torque as well as hp, might be the other way around with the torque numbers though...

    But i'm pretty sure that backpressure has something to do with it...

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    did you only run once on the dyno per time? or those numbers were the best out of x runs (per time)? reason i ask is 7hp is not much variance, could be due to better fan placement or better cooldown, who knows? engines tend to vary output by a small margin, which is why people do multiple runs to get a high and an average.
    Click here to enlarge
    2007 335i Coupe
    Mods: Check the Garage

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    1 out of 1 members liked this post. Reputation: Yes | No
    Best out of 5 runs... did 5 runs both times....

    all the runs with the cat on showed increased power, if i recall the lowest hp on the runs we did post cat install was 307hp.. best was 311,

    lowest pre cat install was 299hp, and as stated before best pre was 304..
    Last edited by angelic0-; 09-13-2011 at 12:19 PM.

  16. #16
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    Click here to enlarge Originally Posted by angelic0- Click here to enlarge
    Best out of 5 runs... did 5 runs both times....

    all the runs with the cat on showed increased power, if i recall the lowest hp on the runs we did post cat install was 307hp.. best was 311,

    lowest pre cat install was 299hp, and as stated before best pre was 304..
    Do you have the graphs?

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Do you have the graphs?
    I've already mailed my friend on the subject 8)

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    Click here to enlarge Originally Posted by angelic0- Click here to enlarge
    I've already mailed my friend on the subject 8)
    Thanks.

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    Click here to enlarge

    Three best non-cat runs and the best run with cat...

    9hp increase Click here to enlarge i rest my case !

    and there were four runs pre and post..

  20. #20
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    Click here to enlarge Originally Posted by angelic0- Click here to enlarge
    Click here to enlarge

    Three best non-cat runs and the best run with cat...

    9hp increase Click here to enlarge i rest my case !

    and there were four runs pre and post..
    It's interesting, definitely, and may just be variance from run to run.

    Honestly, going to an X-pipe to remove one set of cats or ditching cats completely is a mod that produces a lot of power on the M3 and basically every motor so I can't explain it.

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    i beleive it had either something to do with backpressure OR the O2 sensors behind the cats were signaling a limp mode without the cats... BUT... in that case... we would have been seeing a lot less horsepower !

  22. #22
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    pretty quiet for having full straight pipes Click here to enlarge definitely need a tune if you are looking for more power, or just do some swap lol
    Click here to enlarge

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