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Bypass valve/Y pipe

Discussion in '348/355' started by jimmym, Mar 30, 2014.

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  1. jimmym

    jimmym Formula 3

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    #1 jimmym, Mar 30, 2014
    When the bypass valve opens up and exhaust gases flow through the muffler, does anyone have an idea how much of the exhaust gas flows through the y pipe compared with the primary pipes? Is it 1/3 or do the primary pipes still flow more than the Y pipe?

    I was considering about having a muffler built. Combining a challenge exhaust with a more traditional exhaust. Keeping the primary exhaust pipes separate from the Y Pipe. Each set of pipes having their own muffler.
     
  2. Mitch Alsup

    Mitch Alsup F1 Veteran

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    #2 Mitch Alsup, Mar 31, 2014
    Probably about 60% though the Y-Pipe.
     
  3. Evan.Fiorentino

    Evan.Fiorentino F1 Rookie

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    #3 Evan.Fiorentino, Mar 31, 2014
    Last edited by a moderator: Sep 7, 2017
  4. jimmym

    jimmym Formula 3

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    #4 jimmym, Mar 31, 2014
    Thanks Mitch for the info. Wasn't there a thread a while back where Capristo described how the factory exhaust/bypass system worked and how they developed their mufflers for the 355? I thought he stated that the Y-Pipe and the primary exhaust should be separate. I read this quite a while ago so I could be wrong.

    Evan I have an aftermarket Y-Pipe but decided to keep my OEM one on the car for now. I recently purchased another OEM Y-Pipe and gutted it. I may eventually put that one on.
     
  5. gothspeed

    gothspeed F1 World Champ

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    #5 gothspeed, Apr 1, 2014
    There are many things which can affect this 'percentage' ....... many things ..... :eek:

    ° which headers are used, the divergent rate/angles/bends at which the collector exit splits off into the separate paths, is each path equal in that respect?

    ° which cats are being used, ceramic or metallic, how many cells per inch, what is the flow area and length of the catalyst matrix?

    ° the shape and merge rate/angle of the y-pipe and how much flow area is allocated per bank before the bypass? what size is the tube post merge? is there a divider in there? how long is it? .... Example; stock 2.7 y-pipe has a pretty long divider till just before the bypass valve

    ° number of bends in each path, flow area of each path along the way and how long is each path overall?

    Then;

    ° what happens after the bypass and the cats, has its own set of similar factors ..... the factors above and some I missed, will affect that ultimate 'percentage'

    ° finally ..... sound preferences and goals ...... what sound attenuation methods are being used and how are they applied?


    But, if you are just looking to put a muffler together to quiet the engine and not too concerned about a well planned, fully optimized system ...... then disregard most of this post ...... :eek:
     
  6. jimmym

    jimmym Formula 3

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    #6 jimmym, Apr 1, 2014
    Oz, I was hoping that you would reply given the fact that you have experimented with a few different exhaust systems for the 355. I am not as concerned about sound as much as a well developed system. Are there any advantages of keeping the bypass and the main exhaust separate?
     
  7. jimmym

    jimmym Formula 3

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    #7 jimmym, Apr 2, 2014
  8. gothspeed

    gothspeed F1 World Champ

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    #8 gothspeed, Apr 3, 2014
    Jim, without going into exhaustive details and speaking strictly from a cat-back perspective. One of the primary goals in proper exhaust design, is to make sure the ECU is getting accurate and timely information from the o2 sensors. So essentially maintaining a representative exhaust flow over the o2 sensors at all times, (example; during closed and open bypass positions). This maintains proper A/F ratio as intended by the ECU program, for given operating conditions. When proper A/F ratio is the case, the life of the engine and exhaust components is less likely to be hastened ...... at least not by improper A/F ratio ..... ;)
     
  9. jimmym

    jimmym Formula 3

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    #9 jimmym, Apr 3, 2014
    Oz, have you ever taken a factory muffler apart? Is the Y-pipe kept separate from the main exhaust? Are the main pipes kept separate as well or do they merge inside the chamber?
    On Capristo's exhaust system ,the main pipes are kept separate from the y-pipe.
     
  10. gothspeed

    gothspeed F1 World Champ

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    #10 gothspeed, Apr 4, 2014
    Last edited by a moderator: Sep 7, 2017
    I have seen a thread on here that showed an OEM muffler diagram of the internals. It showed the bypass and primary flow ultimately share all four tips, with the bypass having a more direct path.
    But getting to the point, one can create a 'proper' 355 exhaust using either the 'shared' or the 'separate' method. Keeping the exhaust paths 'separate' after the bypass and cats, in and of itself, is not a 'golden bullet', it is only one design variation.

    That said .......... I have designed 355 exhaust systems using a few 'methods' .......... ;)

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  11. jimmym

    jimmym Formula 3

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    #11 jimmym, Apr 4, 2014
    Thanks Oz. That was what I was wondering about. It was after reading that article from Capristo that made it sound imperative that the y-pipe and main system be kept separate in order to prevent excess heat build up and ruined headers. It seems that this may not be the case. Thanks again.
     

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