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Dangers of driving with blown Headers

Discussion in '348/355' started by Yassa, Mar 24, 2012.

  1. Yassa

    Yassa Formula 3
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    May 23, 2011
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    Hi Guys,

    Just wondering what the dangers of driving with blown headers is?... There's a lot of stuff on here about symptoms but I was curious about the damage it can do, and symptoms of such damage.


    Thanks
     
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  3. ~Joshua

    ~Joshua Karting

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    One of the most expensive damages caused would be the eventual erosion of the seal exhaust valves have on their seats when closed.

    Over time you might notice poor performance, perhaps a CEL for o2 issues or misfires, and a serious repair bill.
     
  4. bobzdar

    bobzdar F1 Veteran

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    O2 sensor will think the engine is running lean and over ritchen the mixture overheating the cats and potentially washing down that bank?
     
  5. Yassa

    Yassa Formula 3
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    Yikes...pretty nasty stuff! Best to replace the OEMs as they're bound to fail at some point.

    Thanks
     
  6. pcarcraig

    pcarcraig Rookie
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    There's always unburned fuel in the exhaust after the combustion cycle is complete, which the catalyst is supposed to burn before the exhaust enters the atmosphere. If air enters the exhaust system prior to the catalyst, then the remaining fuel can burn, and it could do so at a point near the valves. I've read this a few times over the years, and the suspicion that the failed headers lead to excessive exhaust valve temperatures, and hence failures. Might not be such a problem on 4-valve Ferraris, but the 5-valve 355 has a smaller valve seat, and hence less thermal conductivity between the valve and head. So I've always suspected the increased thermal load in the case of a cracked manifold is a good candidate for the root cause of the high level of valve failures on the model.
     
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  8. m5guy

    m5guy Formula 3
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    #6 m5guy, Mar 25, 2012
    Last edited: Mar 25, 2012
    Craig, no offense but I think you've combined a bunch of conditions and parts in that statement that makes your point confusing. The catalytic converter is not burning anything (unless you are referring to the chemical reaction inside the cat as combustion.) The "unburned fuel" enters the cat as a HC mixture because it is the byproduct of a combustion cycle that is not 100% efficient. It gets chemically converted to CO^2 and H^2O. It's the EGR valve (aka non-return check valve) that pulls some of the exhaust stream ahead of the catalyst and re-circulates it back into the intake to be re-burned.

    The often posted cause-effect of a blown header on the F355 is:
    - Poor materials and construction causes header primary to break open.
    - Negative pressure following the exhaust pulse causes fresh air to get sucked back into cracked header and causes the pre-cat O2 sensor to give a false voltage reading.
    - ECU interprets that voltage signal as a lean condition and increase fuel delivery.
    - Excess of fuel washes the cylinder wall of lubrication and promotes premature wear and damage in that cylinder.
    - Compression in that cylinder drops as the wall and rings no longer maintain minimum tolerance.
    - Blowby pressurizes crankcase and contaminates oil supply. Engine starts burning oil excessively.

    If I got this wrong and any other 355 owners want to chime in, please do. This is how the condition was described to me when a bulging header tube was discovered in my car during the 30K major. In addition, there is a post from last year from a NE owner and subscribed member Hezgon who's engine was rebuilt by Competizione due to damage caused from a broken header. If I recall correctly, the major damage was on the bottom end, not on the head. Maybe someone like David Helms can comment further, but valve failures do not seem to be a known issues with these motors. Valve GUIDE wear is, but that is another topic altogether.
     
  9. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
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    The 02 sensor is NOT giving a false reading.

    It is giving a reading of the true exhaust gas O2 content plus the true air leakage O2 input. Just like it is supposed to. It is just that this voltage will tell the ECU that the mixture is too lean, when in fact the mixture might be perfect.

    That is, the O2 sensor is correctly reading the actual O2 in the gasses flowing by, but that the gasses flowing by are not 100% from the cyclinders of the motor.

    The rest of your story line holds up.
     
  10. m5guy

    m5guy Formula 3
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    Yes, that is what I meant by "false" but your wording is better. It is a signal that is not 100% from the cylinder.
     
  11. James-NZ

    James-NZ F1 Veteran

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    A friend of mine had this happen, it gets nasty expensive very quickly, making replacement headers seem great value for money.
     
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  13. pcarcraig

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    #10 pcarcraig, Mar 27, 2012
    Last edited: Mar 27, 2012
    m5Guy,

    I am actually referring to the catalytic converter completing the burn cycle of the excess hydrocarbons (HC) that make it down stream of the combustion chamber. The reaction in the catalytic converter is HC+O2 => H2O + CO2 (sorry if the reaction is unbalanced), along with excess heat, and so I said it "burns" the excess fuel for simplicity. Apologies if I didn't state it clearly before.

    The point I was trying to make, is that a cracked exhaust manifold can allow oxygen from the atmosphere to enter the manifold and combine with the excess unburned fuel (i.e. HCs) from the combustion chamber. This combination can burn and produce heat resulting in high temperatures near the exhaust valves, and exhaust valve failure.

    I've posted links to a few post that noted a correlation between failed manifolds, and exhaust valve failures.

    http://www.ferrarichat.com/forum/showpost.php?p=136149284&postcount=108

    http://www.ferrarichat.com/forum/showpost.php?p=136149361&postcount=114

    http://www.ferrarichat.com/forum/showpost.php?p=136173076&postcount=24

    http://www.ferrarichat.com/forum/showpost.php?p=138201644&postcount=76

    All the above post are a few years old, and perhaps thinking has progressed since then. If that's the case, I look forward to hearing any new findings.
     
  14. gothspeed

    gothspeed F1 World Champ

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    +1 ..... this sequence of events ( I get what you meant by the o2 false voltage reading ;) ) is what I have deduced from first hand experience on a few 355s .......... there are a couple other things I am suspecting as well ....... will be doing tests to verify if they hold true ............ will write up any findings should they materialize ..... :eek:
     
  15. MS250

    MS250 Two Time F1 World Champ
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    #12 MS250, Mar 30, 2012
    Last edited: Mar 30, 2012
    Short answer...Don't drive with blown headers !
     
  16. cavlino

    cavlino Formula 3

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    Correct and this issue should be known well enough now that shops should be changing aged 355 headers as preventative maintenance (understatement here big time) during a major service :(
     
  17. LmnsBlu355

    LmnsBlu355 Formula Junior

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    I agree that changing out blown headers immediately is the way to go.

    Its been well described here on Fchat what to look for with blown headers.

    But is it possible to monitor the the fuel being delivered to each cylinder bank in real time to detect when a "false lean" condition is triggering increased fuel flow before cylinder wash occurs?
     
  18. brian.s

    brian.s F1 Rookie
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    Yes, you could monitor fuel trims bank to bank. However, I am not sure anyone can tell you the critical point. Better to fix when needed, ie when they first crack. Then check all other factors to eliminate other causes for the failure in the first place.
     
  19. ready321now

    ready321now Formula Junior

    Jan 5, 2013
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    I drove approx - miles on a blown LH manifold. The car doesn't sound much different....ie there is no ticking at idle or loud, obvious or abnormal sounds.

    What are the chances I did damage to the mtor? I have not driven it since realizing the problem (seeing insulation dust on the engine bay, left side.

    Quite worried about this since I just got this car recently.

    Any help guys?
    Losing sleep over this....
     
  20. SoCal1

    SoCal1 F1 Veteran
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    If you caught it early you sound OK, I would not worry if your numbers were good
    Just check again so you can sleep

    :)
     
  21. ready321now

    ready321now Formula Junior

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    Actually... the compression test was done before the manifold self destructed ....
     

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