By-Pass Pipe and Valve?? | FerrariChat
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By-Pass Pipe and Valve??

Discussion in '348/355' started by bcwawright, Feb 23, 2007.

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  1. bcwawright

    bcwawright F1 Veteran

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    #1 bcwawright, Feb 23, 2007
    Is there really a need for the by-pass pipe and valve on the 355? I am not looking for low sound levels.......has anyone done a header without the top part that connects to the by-pass pipe? Does it make any sense to just make the exhaust as straight as possible.......the by-pass pipe and valve sure do put alot of heat in the engine bay...especially around the intake hose/air box/plenum...
    Any thoughts before I start this project???

    Thanks
    Bruce
     
  2. chaa

    chaa F1 Veteran

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    #2 chaa, Feb 23, 2007
    Its all about emissions, both air and noise. If you can do a system that can meet your countries/areas emissions then knock ya self out. I suspect in an ideal world ferrari would have done it different. But red tape and BS dictates;)
     
  3. UConn Husky

    UConn Husky F1 Rookie

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    #3 UConn Husky, Feb 23, 2007
    http://www.ferrarichat.com/forum/showthread.php?t=138523

    Check out this bit I posted...Ferrari says the exhaust backpressure control was designed to improve midrange torque. Makes some sense to me, but not sure on how much it helps. Maybe you can prove it for us, compare dyno pulls before and after! :)
     
  4. bcwawright

    bcwawright F1 Veteran

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    #4 bcwawright, Feb 23, 2007
    I worked on Porsche 935 and 962 turbo race motors for 10+ years and never crossed over the exhaust(the turbo acted in the same way to restrict the exhaust flow but each exhaust was seperate)...only the intake plenum was common to both cylinder banks. I know that Drag racers don't crossover the exhaust..not sure about NASCAR. Seems like I remember the F355 Challenge cars did away with the by-pass valve but kept the by-pass pipe and then hooked up an exhaust pipe to it that had an inline restrictor.....the bottom pipes that connected to the cat by-pass tubes were straight thru....you can see this on the factory challenge exhaust that is listed on eBay.
    I wonder if anyone has opened up the stock by-pass pipe to see what restrictions are in it(the two buldges that look like mini resonators)????

    When it is all said and done$$$$$$$...only the dyno will settle the issue once and for all.........just trying to save time and money before tackling this project and know that the people on this forum have alot more on the ball with F cars than I do.

    Bruce
     
  5. J. Salmon

    J. Salmon F1 Rookie
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    #5 J. Salmon, Feb 23, 2007
    I don't think the bypass valve has anything to do with crossing over the exhaust, but instead frees the flow at higher rpm. At low rpm, some back pressure is good for torque. At high rpm, it's all about unrestricted flow rate, hence opening a second pathway.

    Crossover exhausts are used with V8's that have a standard crank, so you can tune the pulses and get consistent scavenging. An example would be a Pantera or GT40 exhaust (not the Ford GT, it doesn't cross over) with the "bundle of snakes" that has pipes cross from one side to the other. A flat crank V8 does not need to cross over to get the same scavenging effects.

    At least that's what I heard...
     
  6. bcwawright

    bcwawright F1 Veteran

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    #6 bcwawright, Feb 23, 2007
    Ferrari PN170683 appears to be a sleeve that did away with the by-pass valve on the 355 Challenge cars.....if you are using the Special Exhaust(PN167003) the primary flow from the headers is unrestricted.......the stock by-pass pipe(which appears to have some sort of restrictor) connects to the upper part of the Special exhaust which also appears to have some sort of restrictor in it..........this set-up, seems to be just the opposite of a street car exhaust which restricts the primary flow at low rpms and at higher rpms opens the by-pass valve to free up the exhaust flow. Kinda confusing....but the point being did Ferrari do this for emissions?? and noise at the expense of hp and revs? Since the headers are designed to take care of the scavenging in a normally aspirated engine how much back pressure is needed to get an increase in mid range torque(would love to see this torque figure on a dyno chart)............it has been my experience that back pressure doesn't let the engine rev as quick and limits revs at the top end.
    I saw a post on this forum showing a Japanese design that replaced the stock by-pass pipe with a non restricted one,used a modified by-pass valve(it opens sooner than stock) and did not connect the exhaust pipes from the by-pass to the muffler(Kreis-seig??). This system appears to be much less restrictive than a Tubi(even the racing version) and was wondering if anyone had dyno charts of the two for comparision???

    Bruce
     
  7. gothspeed

    gothspeed F1 World Champ

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    #7 gothspeed, Mar 20, 2007
    I am working on a 360 style exhaust system for the 355...... ;)
     
  8. bcwawright

    bcwawright F1 Veteran

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    #8 bcwawright, Mar 20, 2007
    It's about time.....now get to work
     
  9. DMOORE

    DMOORE Formula 3

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    #9 DMOORE, Mar 20, 2007
    Here's a little food for thought. I wired my exhaust valve open in my 355, because I liked the sound. And guess what, the motor reved faster at low RPM's than it did with the valve closed. Seems to go against the need for backpressure theories. I personally think, Ferrari did it to meet the drive by sound test. 60 MPH in top gear and the valve is closed. No other reason.
    BTW I have not dyno'ed to confirm.

    Darrell.
     
  10. Llenroc

    Llenroc F1 Veteran
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    #10 Llenroc, Mar 20, 2007
    Bruce, I have the factory challenge exhaust still on my 355C. The exhaust layout for the upper pipe is designed for the 2.7 cars not the 5.2 version(the headers are slightly different for each version). The 2 bulges in the street exhaust are cats, in the challenge ex. they are blank/open. The lower ch ex. has the the factory cats in place same as the road cars. When I first tried my car on the street the CELs would come on at low rpm and go off above 3500. What was happening was the upper exhaust on the 2.7 cars flows better that the lower. The upper exhaust flows so well it was actually causing the lower to flow backwards drawing outside air the wrong way thru the cats and over the 02 sensers causing an out of parameter reading to ECU and turning on the CELs. Not until the exhaust out flow presure was hi enough did the 02 sensors start to get enough flow over them, the right way, did the lights turn off. Hope that helps you for info. There is more to this story I just got tired of typing, hahah. If you have anyother questions and I could help let me know. Regards,Vern
     
  11. gothspeed

    gothspeed F1 World Champ

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    #11 gothspeed, Mar 20, 2007
    This is true it happened to me when I wired my bypas valve open. Though mine is a 5.2.
     
  12. DMOORE

    DMOORE Formula 3

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    #12 DMOORE, Mar 20, 2007
    My CEL also triggered. Sounded good though.


    Darrell.
     
  13. bcwawright

    bcwawright F1 Veteran

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    #13 bcwawright, Mar 21, 2007
    Hi Vern....please read some additional posts on thread "335 engine with 360 parts".
    Failed valve guides,broken headers,bad cats and O2 sensors,extremely high under hood/engine bay temperature.....part or all of this could be contributed to the bypass system on 355.
    If outside air is being sucked into the primary exhaust where main cats and O2 sensors are at, and engine exhaust is being forced out thru bypass wonder what happens....from mid to WOT is O2 disabled and ecu reading an installed default....if the mixture is rich and you are blowing air in via the auxillary air system(this is located at the proximal end of header primaries) you will have an extremely high egt......also remember that the thermocouple sensors are only located in the primary and not the secondary(bypass) exhaust system.

    Challenge cars had to run the bypass system because of rules but the bypass "valve" was allowed to be removed......the cats were basically hollow...and the aux. air system was removed(???)......the engines did have the iron valve guide upgrade for longivity due to full race conditions....but headers appeared to be stock.......and as far as I know the headers did not fail like street car.
    The 355 did rev quicker and had better throttle response with bypass valve eliminated.......but IMO we are talking in this thread about a complete reworking of the 355 exhaust that would eliminate the bypass pipe and valve, get rid of aux air sys., and go with a cat(hperflow) or straight thru pipe with 360 hdrs, and a much less restrictive muffler which could even have the bypass on it like the f40/50 and 360/430.
    Much more to think about but believe this is heading in the right direction.

    Bruce
     
  14. gothspeed

    gothspeed F1 World Champ

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    #14 gothspeed, Mar 21, 2007
    The aux. air is only "on" during warm up. I will be running 360 headers with "high flow" cats. My only decision now is to run an X-pipe/balance pipe or just go straight through "independant" on each side. :eek:
     
  15. bcwawright

    bcwawright F1 Veteran

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    #15 bcwawright, Mar 21, 2007
     
  16. gothspeed

    gothspeed F1 World Champ

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    #16 gothspeed, Mar 21, 2007
     
  17. bcwawright

    bcwawright F1 Veteran

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    #17 bcwawright, Mar 21, 2007
     
  18. Llenroc

    Llenroc F1 Veteran
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    #18 Llenroc, Mar 21, 2007
    Bruce I think you misunderstood my intent of my response. I was just relaying what my system did and how free flowing the upper part of the 355 exhaust system is. I have thought about switching to a 360 header too(It will fit from what I understand) but wanted to keep my car correct for historical reasons so I tried to get mine factory CH system to work as well as it could. It is a factory CH car, not that means anything but anyway. My exhaust does not have the lower cats or the temp sensors and no muffler other than the addition of header baffles in the upper Y pipe to cut down on a resonance at 2500 rpm and to add just enough back pressure to push exhaust thru the lower system at low rpms to keep the CELs off. The car runs very strong and is probably not for the faint of heart when it comes to sound levels.
    In your second pharagraph you state that CH cars had iron guides, not all of them did/do mine had bronze guides until a rebuild in 2000, also the headers did not last any longer than street cars from what I have seen. My cars' right side had holes in every pipe at 6500 miles. Sorry to get off your topic of 360 headers I just thought you guys might be interested in a side thought on the 355 system. Regards, Vern
     
  19. bcwawright

    bcwawright F1 Veteran

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    #19 bcwawright, Mar 21, 2007
    Hi Vern
    I really appreciate your posts they are very helpful....that is what is so nice about the brotherhood....we can help each other......I learn something new here everyday about these F cars......look forward to seeing some pics of your car.....I have always wanted a 355CH for weekend track time.
     
  20. gothspeed

    gothspeed F1 World Champ

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    #20 gothspeed, Mar 22, 2007
    Yeah Vern, post some pics of the 355C :eek: :D :D !!!
     
  21. bcwawright

    bcwawright F1 Veteran

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    #21 bcwawright, Mar 22, 2007
    Goth it appears that you will be the first to attempt the 360 exhaust conversion......best of luck...really hope it works...can't wait to see some pics.
     
  22. bcwawright

    bcwawright F1 Veteran

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    #22 bcwawright, Mar 22, 2007
    Hey Vern....is yours a factory CH? What year of production? Was the 6500mlles all race?
     
  23. Llenroc

    Llenroc F1 Veteran
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    #23 Llenroc, Mar 22, 2007
    gothspeed, if you look at page 2 of the 355 registry there is a pic of my car. I would post some others but I have recently moved to Colorado and only have my lap top and there aren't any pics I can uplaod to the site. There was another thread with 335 pics but I can't find it now, anyway there were some pics on it also.
     
  24. Llenroc

    Llenroc F1 Veteran
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    #24 Llenroc, Mar 22, 2007
    Bruce, Yes, mine was built in Jan. 1997 serial no. 108155. The first 6500 were all race miles, the car was ran in 1998 and 1999 challenge series and owned by FoSFand FoBH/FoOC(Giacomo Mattioli). It has had a interesting history. It was even flown to Italy to run in the challenge finals in 1998. For being raced as much as it was it was in great shape when I bought it. I have given it alot of TLC and good a home hahaha. Regards, Vern
     
  25. gothspeed

    gothspeed F1 World Champ

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    #25 gothspeed, Mar 23, 2007
    Do you have any pics of the exhaust?? What configuration is the muffler??
     
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