Thread: Gains from 3" downpipe on a stock GTP... opinions?

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  1. #1 Gains from 3" downpipe on a stock GTP... opinions? 
    GTX Level Member Elite6's Avatar
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    Snagged a 3" DP from ZZP during the black friday sale. Car will be basically stock except for intake and ZZP wires. What can I expect and is this mod worthwhile on essentially a stocker? Don't think I wanna go through the bs that seems to come with installing headers.
    2005 E55 - stock
    1999 GTP 2dr - 9" HAI | Headers | 1.84's | 3.4 | Ported SC|
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  2. #2 Re: Gains from 3" downpipe on a stock GTP... opinions? 
    I live here. stealthee's Avatar
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    Gain is minimal in my opinion. Its more about freeing up flow for future mods. I only got my ZZP DP because my stocker came apart at the flex.


    2011 Mitsubishi Lancer GTS - DD mode
    1991 Mitsubishi 3000GT - Many mods to come
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  3. #3 Re: Gains from 3" downpipe on a stock GTP... opinions? 
    GTP Level Member buickman104's Avatar
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    It will help by getting rid of the u-bend. Most cars get KNOCK bone stock from that U-bend.
    2000 Bronze Metallic GTP
    Power :Gen V, 3.6 pulley, 3 inch down pipe, Power log, FWI,and DHP Power Tuner,
    Handling: Vogtland Springs, GMPP sway bars, STBS, 18" Konig backbone, CTS-V Front brakes and GXP rear brakes
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  4. #4 Re: Gains from 3" downpipe on a stock GTP... opinions? 
    GrandPrix Junkie Sandman's Avatar
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    The affects you feel are minimal, if catless you get a good sounding exhaust. But it is an essential mod on these cars if you haven't gone with headers.
    05 Saab 9-2X Linear (Saabaru)
    77 Morris Garage B
    Quote Originally Posted by TLSheff View Post
    You said "I'm done with it"... car says "Oh, really? *trollface*"
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  5. #5 Re: Gains from 3" downpipe on a stock GTP... opinions? 
    GXP Level Member Tuner-Extraordinaire's Avatar
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    I wouldn't advise dropping pulley if that's where this is going.

    Basically your car won't pull as much timing, You might see 5-10whp depending how badly your car was knocking before.
    Whine with your Cheese?
    Stock+Self Tuned. Going for low 14's everyday.
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  6. #6 Re: Gains from 3" downpipe on a stock GTP... opinions? 
    I live here. stealthee's Avatar
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    Considering my stock downpipe didn't have a u-bend, it helped me even less.


    2011 Mitsubishi Lancer GTS - DD mode
    1991 Mitsubishi 3000GT - Many mods to come
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  7. #7 Re: Gains from 3" downpipe on a stock GTP... opinions? 
    GTX Level Member Elite6's Avatar
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    no looking at a pulley drop right now, wasn't even sure if DP and Plog could warrant a drop? I was thinking the DP for now and look at tuning next before anything else.
    2005 E55 - stock
    1999 GTP 2dr - 9" HAI | Headers | 1.84's | 3.4 | Ported SC|
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  8. #8 Re: Gains from 3" downpipe on a stock GTP... opinions? 
    GXP Level Member Tuner-Extraordinaire's Avatar
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    You won't really *need* a tune after a 3" DP as the car will automatically not knock as much as it does stock (3-6* KR), thus providing you with more usable timing (and HP) by removing some of the stock restriction. Personally i think you'd do better getting headers as they not only remove the awful front manifold and crossover on these cars but also serve to remove the u-bend the same as a 3" DP would with the added benefit of futureproofing yourself for further mods.
    Whine with your Cheese?
    Stock+Self Tuned. Going for low 14's everyday.
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  9. #9 Re: Gains from 3" downpipe on a stock GTP... opinions? 
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    My car still had a good amount of KR when I went to a catted 3'' dp.
    I wasn't able to run KR free on the stock pulley with stock timing/AFR (AFR which is actually quite rich) until I got headers.

    Once I got headers I was able to lean out the AFR almost a full point and run an 04+ timing table.



    As someone else said you'll be lucky to see 5-10whp.
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  10. #10 Re: Gains from 3" downpipe on a stock GTP... opinions? 
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    Minimal gains, shouldnt need a tune too bad. I would pick up another easy mod like rockers and then worry about tune.
    Current = Turbo, E85, XP, and Tengis Tune

    Old = L36, ported Gen3, IC, XP, Stock Heads, E85, Headers, and Tengis Tune
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