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3" or 2.5" downpipe?

Discussion in 'Modifications' started by Crystal copen, Aug 28, 2015.

  1. Crystal copen

    Crystal copen Copenworld Member

    Joined:
    Dec 28, 2012
    Hi, would a 3" downpipe & system be too large for a stock copen? It's completely standard at the moment, we might fit an air filter kit and possibly bigger Intercooler at some point (doubtfull though) :( So probably just end up with a new turbo back system.

    Do most go for 3" or better to fit a 2.5" DP & system?

    Thanks Dave
     
  2. trustafox

    trustafox Copenworld Guru

    Joined:
    Nov 19, 2012
    Location:
    East Mids
    Car(s):
    Yes
    I'm not an expert on turbo exhausts, more knowledgeable on NA, I've the 1.3. Yeah 3 would be too big for the NA, but I think it might be for a little engine like the Copen turbo. Although they say big bore exhaust is good for turbos. I think because its post turbo you just want to gases out of there. You are not tuning it for laminar flow and scavenging quite like NA can as the turbo will block that effect back to the cylinder. Pre-turbo I think is a different matter as you want gas flow at some optimum speed to spool the snail. To fast and probably give you too much back pressure, too slow flow/low pressure and the turbo might not move much. The 0.7 only emits so much gas volume, putting a drainpipe on it and the gases might wander around like in a big mansion.

    her is what I have grabbed...

    Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.

    As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”


    So 2.5 inch DP is not needed. go for 2 inch.
     
  3. Crystal copen

    Crystal copen Copenworld Member

    Joined:
    Dec 28, 2012
    Thanks, forgot to reply here.

    He couldn't do the down pipe as the bend was to tight/short into the cat and didn't fee the need to upgrade it. So we've just had a cat back system fitted instead. Not much louder Han standard tbh so it might go back in and have the silencers changed for something a little louder
     
  4. trustafox

    trustafox Copenworld Guru

    Joined:
    Nov 19, 2012
    Location:
    East Mids
    Car(s):
    Yes
    How can the manufacturer do the bend then and he can't? does he just use his hands? Can he not do a long piece and cut it shorter? :wondering: Get some of that aluminium ducting! :rock:
    I think its not very low because its an ickle 0.7! :p Now if you had the big boy 1.3 :giggle:
     
  5. Crystal copen

    Crystal copen Copenworld Member

    Joined:
    Dec 28, 2012
    I'll have to ask him mate, I think he felt with the distance between the turbo flange & cat it wouldn't make much difference fitting a thicker DP? (Something like that anyway! Was hanging getting dragged around the shops all day by the missus by then so just say yeah ok....I'll be right there to collect it!!
     
  6. trustafox

    trustafox Copenworld Guru

    Joined:
    Nov 19, 2012
    Location:
    East Mids
    Car(s):
    Yes
    thats probably the area it makes the difference! to get that high pressure/velocity gas out the turbo. Back it up means its static so the turbo doesn't spin. Or it goes through the wastegate and that means no boost. Allow the post turbo pipe to accept all the gas the turbo is throwing at it.
    Big 9 inch tail pipes do sweet fanny adams. Once its passed the silencer there is little to gain or lose in comparison.
     
  7. trustafox

    trustafox Copenworld Guru

    Joined:
    Nov 19, 2012
    Location:
    East Mids
    Car(s):
    Yes
    although twin tail pipes looses hp
     
  8. Liam Bradshaw

    Liam Bradshaw Copenworld Member

    Joined:
    Aug 10, 2015
    Location:
    Runcorn, UK
    Car(s):
    Copen 659cc turbo
    I had mine in at an exhaust place the other day and they said they wouldn't even bother with making a downpipe as the price would be comical due to the flange on it having to be custom made so they're just gonna smash all the cat out instead then do me a 2" system with no silencers. Already has no silencers in but the guy who made it was possibly the worst welder in the world and used crush bends D:
     
  9. Dave Hardwick Engineering

    Dave Hardwick Engineering Copenworld Newbie

    Joined:
    Oct 19, 2014
    Location:
    Shepshed, Loughborough.
    Car(s):
    VX220 Turbo
    I have made a 3" system on my VX 220 turbo using a Garrett 28/67 that is pushing out in excess of 400 BHP and 375 lbs of torque with no problems. 2.5" systems on the same cars are only a restriction approaching 300 BHP. I would think a 2" system would be plenty large enough.

    Dave
     
  10. Dave Hardwick Engineering

    Dave Hardwick Engineering Copenworld Newbie

    Joined:
    Oct 19, 2014
    Location:
    Shepshed, Loughborough.
    Car(s):
    VX220 Turbo
  11. marnob

    marnob Copenworld Regular

    Joined:
    Aug 7, 2014
    Location:
    Gold Coast, Australia
    Car(s):
    Copen L880K 2004
    For those wanting to modify the exhaust just stick to a 2" down pipe, cat back.
    It is easily fitted and re welded to the original flange by a capable exhaust shop. Remove the middle muffler in the process and run the pipe all the way to the back muffler and weld it there.
    Leave all the rest as is. Makes no difference with the slightly smaller diameter pipes and distance to the rear.
    Super cheap mod to gain more power.
    You will find the exhaust note will change after its run a couple of times and I felt more power after 100kms or so.
    If its a bit loud for you, just add a small silencer.
    Seems the ECU needs time to adjust to the better exhaust air flow.
    Make sure they put the O2 sensor in the exact same place/distance it was before.
     

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