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Thread: Exhaust Size for Boost/Power?

  1. #1
    Join Date
    Apr 2014
    Location
    Cardiff, UK
    Posts
    291
    My Cars
    E39 528i, E46 325ti

    Exhaust Size for Boost/Power?

    Hi All, just wondering what amount of boost/power a 2.5" exhaust would support from your experiences?

    Car is an e39 with stock M52B28 Euro, single vanos, DIY turbo build with a fairly small Garrett diesel VNT turbo(.64 AR hot & cold), 2" outlet on the turbo with 2"-2.5" downpipe, then 2.5" system all the way back to one backbox(butchered stock box) with no cats.

    I'm looking at changing my back box and just wondering if it's worth changing the whole system to be 3" now or if 2.5" is enough for the moment. My current boost levels are about 8.5psi dropping to 5.5psi at high revs and car made 256fwhp at 5.5psi. I'd only be looking to run 10-12psi max due to stock compression etc.

    Do you think 2.5" exhaust would be ok for my current goals or should I change to a 3" system? I know at some point I'd need to change the turbo and downpipe due to restrictions there, but that's a long term goal with lower compression etc etc which won't happen any time soon.

    Any info/help would be great.
    Cheers
    Rob

  2. #2
    Join Date
    Jul 2007
    Location
    poconos pa
    Posts
    1,165
    My Cars
    e36 m3, turbo e36
    If you could afford to do the 3 inch exhaust now I'd recommend doing that. The 2.5 will work but the 3 inch will work better. Less back pressure, better spool, more power and has a lot more potential when your ready to make more power.


    -sold...replaced by turbo e36

  3. #3
    Join Date
    Oct 2010
    Location
    Manchester, N.H.
    Posts
    16,712
    My Cars
    96 332IS 6466 turbo
    Can you post the specs on that turbo before changing, or tossing money into fabricating a down pipe to fit a turbo that may be your choke point.
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
    Your 1 and only stop for all your BMW performance needs
    WWW.CESMOTORSPORT.COM

  4. #4
    Join Date
    Apr 2014
    Location
    Cardiff, UK
    Posts
    291
    My Cars
    E39 528i, E46 325ti
    Thanks both, the turbo is a Garrett GTA2559V, iirc it's only got a 2" inlet and 2" outlet and is .64AR on both hot and cold side. I've removed the VNT actuator and just locked the vanes in place. I'm only using it as I picked it up cheap on ebay. A bigger turbo is on the list of things to do but can't afford it atm as just spent money on tyres for a track day!

    I'll look into the 3" exhaust then as makes sense long term, for now it would probably just be downpipe back though.

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