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Thread: The E21 323i from the scrapyard.... <3

  1. #51
    Join Date
    Nov 2013
    Location
    Gerrrmany
    Posts
    338
    My Cars
    E34 Turbo
    I have 2 questions, maybe you could help me.

    Would like to run a 4" downpipe and a 3" exhaust. There is not enough space to run the 4" down, but would you think i would gain a noticable spool & power benefit from just running like turbo back till the firewall in 4 inch (so maybe 1 foot or so) and then reduce it to 3" ? I would assume i could see some benefits but want to hear different opinions before i decide to do it.

    2.: could a open screamer wastegate pipe cause false AFR readings? i am still running enough exhaust gas to the sensor and would expect no false reading, and plenty of guys running open dump, but just wanted to hear if that could happen somehow?

    thanks. <3

  2. #52
    Join Date
    Jun 2018
    Location
    Florida
    Posts
    19
    My Cars
    240sx
    IMO
    If the turbine outlet is 4" then starting with 4" will help organize the exhaust gas as the turbine was designed with that outlet size/shape in mind, it will also give the exhaust a chance to cool and condense slightly before being subjected to the smaller diameter, lower pressure, higher velocity tube downstream.

    I've never run a screamer but I don't see how venting one portion of well mixed exhaust gas would have any effect on O2 content in the exhaust tube since it isn't getting the chance to be sucked back in the way and exhaust leak would allow.

  3. #53
    Join Date
    Oct 2006
    Location
    Toronto, Canada
    Posts
    2,960
    My Cars
    D3 A8 4.2 - E36 Turbo
    Quote Originally Posted by PowerKraut View Post
    I have 2 questions, maybe you could help me.

    Would like to run a 4" downpipe and a 3" exhaust. There is not enough space to run the 4" down, but would you think i would gain a noticable spool & power benefit from just running like turbo back till the firewall in 4 inch (so maybe 1 foot or so) and then reduce it to 3" ? I would assume i could see some benefits but want to hear different opinions before i decide to do it.

    2.: could a open screamer wastegate pipe cause false AFR readings? i am still running enough exhaust gas to the sensor and would expect no false reading, and plenty of guys running open dump, but just wanted to hear if that could happen somehow?

    thanks. <3
    1. What power level are you at? In general, bigger is always better (to a point)... but 4" is really big so if you're making <600whp then 3" is more than fine still... 3.5" is probably a better choice either way for you.

    2. No.

    E36 DYNO TUNING WIRING PARTS

  4. #54
    Join Date
    Nov 2013
    Location
    Gerrrmany
    Posts
    338
    My Cars
    E34 Turbo
    Quote Originally Posted by Kingtal0n View Post
    IMO
    If the turbine outlet is 4" then starting with 4" will help organize the exhaust gas as the turbine was designed with that outlet size/shape in mind
    Its got a 3" Outlet, but i would go 3" to 4" with a smooth transition, then back to 3" to fit down there and 3" all the way back. I would think i could see gains from even that short bit of 4" pipe (approx 2 feet of 4" maybe?), as it offers a noticable bigger volume right after the turbine... not sure if thats just theory and not worth the cost of extra pipe and work.

    - - - Updated - - -

    Quote Originally Posted by NOTORIOUS VR View Post
    1. What power level are you at? In general, bigger is always better (to a point)... but 4" is really big so if you're making <600whp then 3" is more than fine still... 3.5" is probably a better choice either way for you.
    Shooting for daily 400-500 wheel and the sky is the limit on the dyno. or my stock pistons and rods.
    But improved spool up would really be nice of course.
    I will not buy 3.5 all the way thru, as i got a nice bit of 3" left, but a 3,5 Downpipe should be doable and maybe even fit thru the tight space between rack and firewall, what a 4" would not.... hmmm... unsure what to do.

    2. No.
    thanks

    - - - Updated - - -

    For everyone that is too lazy to klick thru this thread but still likes pictures. I will add more of those dia shows soon.



    Episode one of my build. The rescue from the scrapyard and welding.

    https://www.youtube.com/watch?v=E-Qx...ature=youtu.be

  5. #55
    Join Date
    Jun 2018
    Location
    Florida
    Posts
    19
    My Cars
    240sx
    IMO

    Never increase and then decrease diameter of (turbocharger) exhaust gas plumbing unless you have an extremely good reason to slow it down (velocity loss), de-organize it (entropy loss)/ add turbulence, as this is surely going to negatively impact performance.

    Remember that mass flow in = mass flow out

    If you put a giant room in the middle of two small pipes it probably won't help with massflow on either end unless you've timed some kind of acoustic pressure wave (i.e. expansion chamber on a 2-stroke) in relation to an opening/closing orifice which a turbine does not... really have
    Last edited by Kingtal0n; 07-13-2018 at 04:08 PM.

  6. #56
    Join Date
    Oct 2006
    Location
    Toronto, Canada
    Posts
    2,960
    My Cars
    D3 A8 4.2 - E36 Turbo
    Quote Originally Posted by PowerKraut View Post
    Shooting for daily 400-500 wheel and the sky is the limit on the dyno. or my stock pistons and rods.
    No need at all for larger than 3" in that case...

    E36 DYNO TUNING WIRING PARTS

  7. #57
    Join Date
    Nov 2013
    Location
    Gerrrmany
    Posts
    338
    My Cars
    E34 Turbo
    Turns out the s300sxe Got a Strange Flange. No way 3" vband.. more like 3.5 but 3 inside diameter...

  8. #58
    Join Date
    Jun 2004
    Location
    The D, MI
    Posts
    1,294
    My Cars
    97 M3, 98 328i, 13 Cruze
    This is the one I used. 4.21 marmon flange if you want to search for others.

    It's a little thin a warps but the clamp seems to bring it square.

    https://rover.ebay.com/rover/0/0/0?m...2F263578553284

    They sell it with and without a clamp

  9. #59
    Join Date
    Nov 2013
    Location
    Gerrrmany
    Posts
    338
    My Cars
    E34 Turbo
    Thanks Kevin!

    Since the turbine got a 3,5" outlet, i decided to go 3,5 downpipe

    Plans are:

    All Stainless of course.
    Downpipe 3,5"
    On the Floor to the rear axle 3"
    Single Muffler right before the rear axle with single 3" inlet and dual 2,5" outlet
    Fit the dual 2,5" thru the rear axle somehow and back to the rear bumper, als the e21 323 came with duplex pipes at the back.

    And in my opinion the 2,5" pipes match the sleeper look better than 3"


    And flow-wise the dual 2,5" (9.81 square inch) offers almost perfectly the same cross area as single 3,5" (9.62 square inch)


    Cant wait to hear that thing run with a proper exhaust.


    What diameter for a proper open wastegate? does it even matter? Its a 38mm Wastegate, so i would of course not go any smaller than that... but would a bigger pipe give any advantage like less creep or stuff?


    e21 07_2018.jpg

  10. #60
    Join Date
    Jun 2004
    Location
    The D, MI
    Posts
    1,294
    My Cars
    97 M3, 98 328i, 13 Cruze
    Yeah that flange just gets cut down a little to get the 3.5" pipe in there.

    s300 flange.jpg
    Last edited by Kevin325i; 07-17-2018 at 07:07 PM.

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