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Thread: Open'd exhaust. How much did you gain?

  1. #1
    turbo addict Turbo Mopar Contributor Dave's Avatar
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    Open'd exhaust. How much did you gain?

    Just curious. By placing a cut out after the downpipe we've consistently removed 3/10 of a second off the 1/4. What have you all progressed from opening your exhaust?

    We usually had either a TII or TI setup running mild boost with fair traction.

    Anyone have any dyno-proven improvements?

    -Bryan

  2. #2
    boostaholic
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    Re: Open'd exhaust. How much did you gain?

    You are correct on the 3/10's
    I added a cutout to the SRT-4, wen from 13.80 to
    13.52.

  3. #3
    boostaholic R/T's Avatar
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    Re: Open'd exhaust. How much did you gain?

    My Son's ( SC 2.5 ) 88 Shadow ES automatic;

    We were running an open 2.25" stock downpipe, went to a 2.5" from an 89 Shelby Daytona and picked up 6/10ths and 4 MPH.

    The Mitsu has the big swingvalve, it *really* likes a big downpipe....

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    Buy my stuff!!!!!!!!!!! :O) Turbo Mopar Vendor turbovanman²'s Avatar
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    Re: Open'd exhaust. How much did you gain?

    On that note, full 3 inch mandrel system with a Magnaflow, I can't see gaining 3/10's??????????
    1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS! 12.57@104 :O)
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  5. #5
    turbo addict Turbo Mopar Contributor Dave's Avatar
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by turbovanman
    On that note, full 3 inch mandrel system with a Magnaflow, I can't see gaining 3/10's??????????
    Of course you still got the restriction of a 3" diameter vs. an open downpipe's amount resistant pressure being only barometric pressure.

    There's literally no restriction in an open exhaust, just about how fast the engine is cranking it out.

  6. #6
    turbo addict
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    Re: Open'd exhaust. How much did you gain?

    What d'you have for an exhaust manifold and turbo SV?

  7. #7
    turbo addict Turbo Mopar Contributor Dave's Avatar
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    Re: Open'd exhaust. How much did you gain?

    I have a MoparzRule heavily ported exhaust manifold and a stock 2.25" '88 SV.

  8. #8
    Admin- "Alexandria" Ken... Comes W/4 Car Garage Turbo Mopar Staff GLHSKEN's Avatar
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    Re: Open'd exhaust. How much did you gain?

    2 1/4" ran a 13.97 @99.98mph Over the winter opened the stock downpipe. Ran 13.27 @ 106.7mph 1st pass. Changed to a Rick D 2.5" ported S/v and open 3" downpipe. Ran 12.85 @ 109.7mph

    On the dyno, full 3" system with a cat and a cutout before the cat. Lost 22ft lbs abd 11whp with the cutout closed.
    Ken Adler....
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  9. #9
    turbo addict Turbo Mopar Contributor Dave's Avatar
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by GLHSKEN
    2 1/4" ran a 13.97 @99.98mph Over the winter opened the stock downpipe. Ran 13.27 @ 106.7mph 1st pass. Changed to a Rick D 2.5" ported S/v and open 3" downpipe. Ran 12.85 @ 109.7mph

    On the dyno, full 3" system with a cat and a cutout before the cat. Lost 22ft lbs abd 11whp with the cutout closed.
    Wow.

  10. #10

    Re: Open'd exhaust. How much did you gain?

    I am running no exhaust now... just open turbo freaking awesome!!!!

  11. #11
    turbo addict
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    Re: Open'd exhaust. How much did you gain?

    My R/T gained 20-25 hp over the entire pull with the cutout open. it's at the end of the downpipe 8-10" before the cat.

    It's a 3" mandrel bent system and at the time the car had a cat on it. Pushed it from 29x whp to 322whp.
    “If the people of the nation understood our banking and monetary system, I believe there would be a revolution before tomorrow morning.” -Henry Ford

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    Buy my stuff!!!!!!!!!!! :O) Turbo Mopar Vendor turbovanman²'s Avatar
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    Re: Open'd exhaust. How much did you gain?

    Nice gains but full 3 inch and Magnaflow, can't be loosing that much. Will have to try that on the dyno. Any bets?
    1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS! 12.57@104 :O)
    1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
    2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
    2004 GSW TDI, 5 speed, fully loaded, modified.

    Aurora ignition wires for sale. Link to info

    Super60 roller cams or custom/billet cams. Link to info

  13. #13
    See me ride out of the sunset... Turbo Mopar Staff BadAssPerformance's Avatar
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    Re: Open'd exhaust. How much did you gain?

    '87 T2 shadow

    Open stock downpipe, cut in front of converter = 13.00's

    Full non-mandrel-bent (read: crimped corners) 3" after downpipe, no converter thru a 3" Dynomax Race Magnum Oval muffler, exit out the back = 13.00's

    JT
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  14. #14
    turbo addict Turbo Mopar Contributor Dave's Avatar
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by BadAssPerformance
    '87 T2 shadow

    Open stock downpipe, cut in front of converter = 13.00's

    Full non-mandrel-bent (read: crimped corners) 3" after downpipe, no converter thru a 3" Dynomax Race Magnum Oval muffler, exit out the back = 13.00's
    What were your 60's and 660's like on both passes? Can you get me both entire slips? That doesn't seem right at all. Either one's pulling real hard on the bottom or the other real hard on the top. Restriction is restriction. And you still had 9.42" x Y (y being whatever the length of the exhaust) of backpressure versus 0 being open.

  15. #15
    Hybrid booster
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by Dave
    What were your 60's and 660's like on both passes? Can you get me both entire slips? That doesn't seem right at all. Either one's pulling real hard on the bottom or the other real hard on the top. Restriction is restriction. And you still had 9.42" x Y (y being whatever the length of the exhaust) of backpressure versus 0 being open.
    I think he's saying the backpressure in a full 3" exhaust is comparable to the backpressure from using a stock dp. Or at least that is what I read from it.

  16. #16
    turbo addict Turbo Mopar Contributor Dave's Avatar
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by The S is Silent
    I think he's saying the backpressure in a full 3" exhaust is comparable to the backpressure from using a stock dp. Or at least that is what I read from it.
    What I got out of his saying is that an open downpipe is equivalent to a 3" mandrel bent exhaust.

  17. #17
    Hybrid booster
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by Dave
    What I got out of his saying is that an open downpipe is equivalent to a 3" mandrel bent exhaust.
    Stock open DP = 3" NON-mandrel bent system

  18. #18
    See me ride out of the sunset... Turbo Mopar Staff BadAssPerformance's Avatar
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by The S is Silent
    Stock open DP = 3" NON-mandrel bent system
    yep, that is what I said...

    Stock open DP = full 3" non mandrel bent with 3" race magnum oval w/o converter

    Entire timeslip is similar for both setups even tried with and without the back seat in the car with the full exhaust setup. Launch at 4000-4500, 1.83-1.85 60'... 13.00-13.10 @ 103-105 mph....

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  19. #19

    Re: Open'd exhaust. How much did you gain?

    It sounds like you were still using the stock DP in both setups? Another way to look at it is that the restriction of the stock DP is such that adding the 3" system had no real effect on backpressure.

  20. #20
    See me ride out of the sunset... Turbo Mopar Staff BadAssPerformance's Avatar
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    Re: Open'd exhaust. How much did you gain?

    Quote Originally Posted by MiniMopar
    It sounds like you were still using the stock DP in both setups? Another way to look at it is that the restriction of the stock DP is such that adding the 3" system had no real effect on backpressure.
    Yep, stock turbo, SV & DP in both. So after that cork, a 3" flowed as good as the open DP

    JT
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    JOIN SDAC and your local Chapter TODAY! - SUPPORT the CLUB that supports YOUR HOBBY!
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