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355 - disconnect exhaust Bypass

Discussion in 'Technical Q&A' started by Ade, Mar 3, 2004.

  1. Ade

    Ade Formula 3

    Jan 31, 2004
    2,095
    UK
    There is another thread about this - regarding the 360. But does anyone know how to do this on a 355 - i.e. wire open the exhaust bypass?? Where to look etc. I had a route around my 355 last night, but I couln't see what to do.
     
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  3. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,944
    You have 2 choices:

    1) use mechanics wire and just hold the valve open.
    2) remove valve and insert pipe of same diameter and end fittings.
     
  4. 355f

    355f Formula Junior

    Nov 1, 2003
    305
    why would you want to do this anyway!

    less torque, more noise ( an not a pleasant one) the 360 is a different story for 355 not something you should do
     
  5. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,944
    Its not so much that you get less TQ, what happens is that there is a hole in the TQ curve in the 2500 RPM-3000 RPM band when the positive pressure wave from the headers arrives with the exhaust and intake valves open. This positive pressure wave blows the fresh mixture out of the cylinder and back up the inatake. The result is noting positive with respect to performance. Away from the hole, the TQ curve is not really hurt.

    Closing the valve prevents the collector (Y-pipe to third muffler port) part of the headers from functioning like a tuned pipe and results in a much lessened pressure pulse (both negative and positive) reducing the ability of bad harmonics from impacting the TQ curve.
     
  6. 355f

    355f Formula Junior

    Nov 1, 2003
    305
    Thanks for the explanation!! I just noticed when using a 'sports exhaust I seemed to loose low down torque and when I wired open the valve it was worse.

    I suppose why would Ferrari go to all this trouble to produce this system only for individuals to wire it open!!
     
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  8. Ade

    Ade Formula 3

    Jan 31, 2004
    2,095
    UK
    OK, I guess I misunderstood from the last post (re: 360). I thought that this was a good way to increase 'good' noise, which I'm all for. But hey, If thats not the case, then I'm certainly not going to pursue this.

    It seems that different people have different views, I'm not really sure what to think now.

    I'm removing my cats next week - that seems to be a good 'well established' way of increasing performance and 'good' noise. Any comments?
     
  9. murph7355

    murph7355 Formula 3

    Nov 30, 2002
    1,691
    SE England Yorkie
    Full Name:
    Andy
    Keep the revs over 5k :)

    PS Sorry. Thought you said "what's a good 'well established' way of increasing performance and 'good' noise."

    Not convinced you're going to get anything massively noticeable just by ditching cats, although I guess they weigh a bit.
     
  10. cinquevalvole

    cinquevalvole Formula 3

    Feb 6, 2004
    1,151
    Germany, Bayern
    Hello 355f,

    we did that on a '95 and on a '96, both EURO Spec GTS with stock exhaust.
    We couldn't notice less torque.
    But the "noise" at low revs is to enjoy. (Matter of taste)
    With open roof you won't really suffer in the cockpit :)
    It's a cheap trick to lift the outlet throttle.
    Every 355 driver can test it for a while. Way back is easy.
    Someone already tested torque with this config on a dynojet?

    forza

    cinquevalvole
     
  11. 355f

    355f Formula Junior

    Nov 1, 2003
    305
    well ive done dyno results with and without cats on my 355 and have the benefit of many people who have done the same thing on this site.

    Removing them makes no difference and if you have a 96 on car may trigger engine check lights but more worriyingly on the dyno results we had the computer did not substitute the ideal values required for best running efficiency. The only way of doing it correctly is to use OBD11 repicators to trick the computer. To the best of my knowledge no one does box for this application.



    If you have a 348 or earlier, yes remove the cats - on a lter 355 DEF not and it makes it noisier as well.

    Whatever you do I can assure you there is NO difference in performance- just as they isnt with K&n filters.
     
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  13. Ade

    Ade Formula 3

    Jan 31, 2004
    2,095
    UK
    Hey Cinquevavole,
    Can you give me any detailed instructions on how to do this?? Where to look (assume I'm a complete novice!)
    Thanks for any help you can give!
    Ade
     
  14. cinquevalvole

    cinquevalvole Formula 3

    Feb 6, 2004
    1,151
    Germany, Bayern
    #11 cinquevalvole, Mar 6, 2004
    Last edited by a moderator: Sep 7, 2017
    Hello Ade,

    1. Do not touch hot exhaust parts :)
    You cant't let it be done ambulantly at your shop because the system needs
    too much time to cool down.
    Usually the gate opens when a certain pressure relation is reached.
    This is around 4.000 revs, but it depends.
    By reducing the cross section it prevents the exhaust gas to go in the muffler
    immediately. We have a barrier/congestion for gas, sound, temperatur.

    2. As you can lift the central gate with your own fingers (upside) you can fix
    it at this complete full open position. (you need much power in your fingers!)
    For testing purposes we use a long strong hose clip. Don't try plastic! Only heavy metal :)
    Later, when decided to keep it forever, you can fix it with a bolt at the lower
    end of the construction where nobody can see it. A simple bolt has to prevent the mechanism to go back in close position.
    Maybe I can take some pics of this issue in a few weeks from my buddy's car.
    But today a have only some pics of my car done.
    On the picture you see what we call "under-inflation-can" (Unterdruckdose)
    with the hose clip applied around. (355 '95 EURO)
    The poor man's sport exhaust is ready to go :)
    Each gas station can do it for you in some minutes.
    What you get is a fine bass at ideling and at rolling between 2500 and 3000 revs.
    You can enjoy the reaction of the engine under every little load.
    If you use a Tubi or a Fuchs behind the "under-inflation-can" you will harvest
    something shocking for your neighbours. No way to find home discreetly :)

    good luck

    cinquevalvole
    Image Unavailable, Please Login
     
  15. Ade

    Ade Formula 3

    Jan 31, 2004
    2,095
    UK
    [You can enjoy the reaction of the engine under every little load.
    If you use a Tubi or a Fuchs behind the "under-inflation-can" you will harvest
    something shocking for your neighbours. No way to find home discreetly :)

    good luck

    cinquevalvole[/QUOTE]

    Thanks very much for all the details!! Its much appreciated. I have not had a chance to try this out yet (as the car is in for a service at the moment), but I'll let you know once I've tried it out and what happens.

    I hope your friend is happy with the results he has got and he has understanding neighbours :)

    Thanks again
    Ade
     

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