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    Feb 15, 2008 4:29:08 PM

    cannga
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    cannga
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    ? for Expert: Could After-Mkt. Exhaust Hurt Power?

    While visiting an independent Porsche shop, I was told that in the case of a turbo engine, something like a bypass pipe could end up decreasing power delivery because it reduces back pressure too much. Could someone with technical expertise explain this please? Is this because too low of a back pressure is detrimental to the turbine's ability to compress air? What parameter is affected, horsepower, torque, or both?

    From one end of the spectrum--very low back pressure of bypass pipe, to the other--high back pressure of stock, I imagine there is a middle ground of Tubi/AWE/Cargraphic exhausts, with mid level back pressure? Is it possible for this middle ground to be worse than stock?

    Thanks in advance.

    Feb 15, 2008 4:33:53 PM

    TT Surgeon
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    Reply to: cannga

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Power?

    Because you lose alot of backpressure, HP will increase, TQ will drop up to a point. Probably much more significant with bypass pipes or a 70mm system.

    Feb 15, 2008 4:34:03 PM

    STRADALE
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    Reply to: cannga

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Power?

    I've read that w/ the 911 Turbo any back-pressure will hurt performance. Less back-pressure = more power. I know this isnt always true w/ N/A engines.

    Feb 15, 2008 4:34:31 PM

    eclou Offline
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    Reply to: cannga

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    No. The statement is incorrect. Where people lose power is if they use too large of a header on a turbo motor. The exhaust flow goes

    motor > header > turbo > exhaust

    for max spool up the pressure differential on either side of the turbo should be maximized. High pressure in the header and low pressure in the exhaust drives the turbine to spool very quickly. Some people will put a very large diameter tubing header on the car and expect gains. Unfortunately this will reduce the pressure and velocity of exhaust gas before it hits the turbine wheel, so the differential in pressure between the header and exhaust is less. The highest pressure differential achieved yields the fastest spool, period.

    Feb 15, 2008 4:43:19 PM

    STRADALE
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    Reply to: eclou

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    At the very end of the Fabspeed video: "PRODUCT VIDEO: 997TT Exhaust Explanation Video"

    "No loss in reducing backpressure only power"
    http://www.fabspeed.com/997TT.html

    But like eclou mentioned this is true as long as it's after the Turbo, the muffler/cats, not prior to the turbo (the headers.)

    What shop said that Cann?

    Feb 15, 2008 4:47:13 PM

    TT Surgeon
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    Reply to: STRADALE

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    I believe he said no loss in power, only reducing backpressure.

    Feb 15, 2008 4:51:06 PM

    edz
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    Reply to: STRADALE

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    Can: If you fool around with the headers and get the wrong cheap kind, it could happen. The 997TT stock headers are prett decent, so keep them as they are and you will be fine. Same concept applies to motorcycles. I know so many people that ended up getting a louder pipe assuming more performance is in the horizon. They found out the hard/wrong way. You need ample pressure to spin your turbins once that's compromised you performance is lost.

    Feb 15, 2008 5:32:31 PM

    STRADALE
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    Reply to: TT Surgeon

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    Quote:
    TT Surgeon said:
    I believe he said no loss in power, only reducing backpressure.



    Nope. He said:
    "just like every other Turbo charged car reducing back-pressure is your objective and king. No loss in reducing backpressure only power"

    Feb 15, 2008 6:33:56 PM

    cannga
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    Reply to: STRADALE

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    Thanks everyone for the helpful replies. So the conclusion is less back pressure is better, and bypass pipe would therefore be best as far as engine's horsepower & torque are concerned?

    Gregg, you are always ready with a URL and info from your careful research! Why do I have this feeling you are going to call Champion about this?
    Cheers.

    Quote:
    STRADALE said:
    At the very end of the Fabspeed video: "PRODUCT VIDEO: 997TT Exhaust Explanation Video"

    "No loss in reducing backpressure only power"
    http://www.fabspeed.com/997TT.html

    But like eclou mentioned this is true as long as it's after the Turbo, the muffler/cats, not prior to the turbo (the headers.)

    What shop said that Cann?

    Feb 15, 2008 7:19:20 PM

    STRADALE
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    Reply to: cannga

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    Quote:
    cannga said:
    Thanks everyone for the helpful replies. So the conclusion is less back pressure is better, and bypass pipe would therefore be best as far as engine's horsepower & torque are concerned?

    Gregg, you are always ready with a URL and info from your careful research! Why do I have this feeling you are going to call Champion about this?
    Cheers.

    Quote:
    STRADALE said:
    At the very end of the Fabspeed video: "PRODUCT VIDEO: 997TT Exhaust Explanation Video"

    "No loss in reducing backpressure only power"
    http://www.fabspeed.com/997TT.html

    But like eclou mentioned this is true as long as it's after the Turbo, the muffler/cats, not prior to the turbo (the headers.)

    What shop said that Cann?






    LoL! I just remembered hearing that in the Fabspeed video when I listened to it a while back. So when you asked it seemed logical to post what I heard.

    Feb 15, 2008 7:19:48 PM

    atomic80
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    Reply to: cannga

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    That's pretty much why adding aftermarket headers don't benefit turbocharged engines much. You'd get more of a benefit from headers in a naturally aspirated engine.

    Feb 15, 2008 7:31:41 PM

    eclou Offline
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    Reply to: atomic80

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    Quote:
    atomic80 said:
    That's pretty much why adding aftermarket headers don't benefit turbocharged engines much. You'd get more of a benefit from headers in a naturally aspirated engine.



    In general, it is true for stock turbos. I used to tell people to think of an engine as a highway system. It will only flow as good as the narrowest section of the road. If your turbos are flowing like a 4 lane highway, adding a 6 lane header won't improve it at all. Now if you increase your turbo size to a 5 laner, a 5 lane header will help.

    Feb 15, 2008 9:57:12 PM

    jeffbco
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    Reply to: eclou

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    Before I changed to the Europipe system I asked the guys there about changing headers - here's their response:
    "We have built and tested headers for the 997 Turbo but we couldn't measure consistent performance gains on the dyno. Couldn't feel any gains while driving the car either. (that was with the sport muffler already fitted). I'm sure it will be great for big hp engines, we won't offer them though."

    Feb 16, 2008 11:10:07 PM

    xandi911
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    Reply to: jeffbco

    Re: ? for Expert: Could After-Mkt. Exhaust Hurt Po

    so if i change the exhaust of my car, like tubi fabspeed europipe.... i will not have HP gain??

    thats the most important....
     
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