Announcement

Collapse
No announcement yet.

3.1L stroker exhaust design options

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    3.1L stroker exhaust design options

    I'm in the process of gathering parts to build up a performance exhaust for a built 3.1L M20.

    I currently have IE long tubes (with 2.25" collectors), a Stromung rear section, and a collection of pipes, U-bends, J-bends, v-bands, an X pipe, and a Borla XS auxiliary muffler.

    Aiming to run catless dual 2.25" back between the two, using the intermediate muffler to quiet it down some and get rid of the drone its current (shitty dual to single to dual) exhaust has.

    I'm struggling to find useful or conclusive information about a couple things, because exhaust design seems to be another version of the "what oil should i run" question.

    1 - Is there a particular place that is known to be good to put an X pipe for this header and displacement configuration? From looking at the OEM exhaust designs, the X is typically directly under the shifter. Interestingly, cheapo aftermarket long tubes usually come with an X section that attaches almost directly at the ends of the collectors, which seems like the complete opposite extreme placement-wise.

    2 - the muffler I've purchased internally crosses the two exhaust streams. Is there any use for having a discrete X pipe section in addition to this? Should I aim for two separate 2.25" mufflers instead?

    3 - the Stromung rear section has 2" pipes, I believe. Any expected issues due to the stepdown from 2.25 to 2?

    4 - O2 sensor placement. I've read a bunch of various things saying that it's best to put it near the collectors, but without doing a X or an H it'll only read one bank. This seems more or less fine, but what are the downsides of putting it further back? Cooler charge?

    cheers
    cars beep boop

    #2
    FWIW, the Supersprint system has an X roughly where the IE long tubes would end, and then separate mufflers.
    cars beep boop

    Comment


      #3
      what camshaft? street engine?
      89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

      new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

      Comment


        #4
        272, and yeah, street. (in an iX that I want to have more grunt and less rod knock)
        cars beep boop

        Comment


          #5
          and yes, the camshaft is undersized. If I had built this motor, I'd have gone with a 280 or 284. However, I am lazy.
          cars beep boop

          Comment


            #6
            I don’t have the answer to your question but I just want you to know I’m rooting for you and you’re handsome.

            Comment


              #7
              how long are the primary tubes?

              with a mild cam on long primaries i think it doesnt matter too much where the X is located. id probably go something pretty close like 17" from the primaries or really long like 64" avoiding in between.
              shorter lnegth primaries dont work well with the x-pipe really close when you have a decent amout of overlap it hurts torque below 3500rpm
              Last edited by digger; 04-19-2019, 06:21 PM.
              89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

              new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

              Comment


                #8
                Originally posted by Danny View Post
                I donít have the answer to your question but I just want you to know Iím rooting for you and youíre handsome.
                thank you, Danny. I appreciate that.

                Originally posted by digger View Post
                how long are the primary tubes?
                about yea long -



                which I've eyeballed to ~35" but can toss a tape onto this weekend
                cars beep boop

                Comment


                  #9
                  Originally posted by kronus View Post
                  thank you, Danny. I appreciate that.



                  about yea long -



                  which I've eyeballed to ~35" but can toss a tape onto this weekend
                  yeah i assumed 34"
                  89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                  new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                  Comment


                    #10
                    Originally posted by digger View Post
                    with a mild cam on long primaries i think it doesnt matter too much where the X is located. id probably go something pretty close like 17" from the primaries or really long like 64" avoiding in between.
                    cool, thank you. this is helpful. I'll see which of those works better placement-wise.
                    cars beep boop

                    Comment


                      #11
                      if you have to fit cats, resonator and muffler having it closer is a bit easier and neater. However its easier to change from the further back to closer position.

                      Further back gives a bit more lowend torque and closer should give a bit more in the midrange, so in effect robbing from Peter to pay for Paul. In your application i think the real effects will be smaller than on others.

                      i would avoid the middle ground as the bottom end will be worse below 2500rpm which to me its counter inituative to build a big stroker that doesnt have bottom end torque
                      89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                      new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                      Comment


                        #12
                        if the muffler is dual 2 inch why not just reduce it at the collectors?

                        the smaller pipe makes packaging that little bit easier, i think a 3.0 m54 has only 2" pipes or smaller shouldnt hurt the flow
                        We're out there in here.

                        Comment

                        Working...
                        X