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  • Blow Off Valves, Reflash and stalling Issues everyone to read.

    I had the opportunity today to do some more research on a colt today with our reflash and have been able to exactly ascertain what we can and cannot do with the stock ECU and Blow off valves.

    This came about as the vehicle had our tune put on with other items, and also had a HKS Sequental externally venting unit, but the vehicle kept stalling after high boost. Research showed it was the blow off valve.

    But first, the techinical explanation

    (A) Blow Off Valves 101 - how they work

    Easy explanation, these vent gases from the pressurised side of the intercooler pipework back to the intake tube between the airflow meter and the turbo from factory. By doing this, the same amount of air is being displaced or moved, so therefore the factory air flow meter does not register a surge of air movement.

    Externally venting BOV's move the same air but of course, vent to atomosphere. When this occures, the factory ECU registers a large volume of air movement, and then immedietly richens up the tune by providing additional fuel due to the calculated load the ecu receives.

    (B) The Factory ECU Managment - how is load calculated and why does this occur?

    Essentally the factory ECU utilises a MAF sensor - Mass Air Flow so the ECU does everything by measuring the VOLUME of air being moved through the engine. That is why any air leaks have immediet dramatic changes.

    When the BOV vents to atmosphere, the ecu registers this massive air flow, equivelent to the vehicle being on 20 psi boost levels and floods the engine with fuel.

    Okay enough technical jargon - down to the nuts and bolts

    Why can some colts run a VTA (Vent to Atmosphere) BOV and some can't.

    Essentially it comes down to air volume. With our first test vehicle, we used a GFB unit, but it was only a small unit so the amount of air being displaced was very small. Because of this engine was able to cope with the additional fuel enrichment without stalling.

    BUt this new customer had a HKS large unit, and every time we had high boost, it stalled immedietly. Quite simply too much air flow.

    This essentially means for colt owners, we still HIGHLY recomend retaining a plumb back Blow off Valve. This means you stay legal with the police and you can be ensured that don't have a stalling issue.

    You can alternativly try a VTA BOV but make sure it is a small unit only. You may get away with it as I estimate probably 50% of the ones on the market will.

    But be warned one further thing, some blow off valves leak off at idle and do not seal properly until they get significant engine boost pressure on them. Not a bad thing with with a plumb back system but with an externaly VTA unit, not good as the car will not idle properly.

    Last information - why does the flash tune not fix this?


    Essentially, we have elimated the error codes on airflow, and other factors. But there is no way with the factory ecu to stop it flooding on rapid gear changes when on high boost as its simply an airflow feature and its integral to the way the ECU does all its calculations.

    Our advice - stay with a plumb back unit or a smaller VTA unit. Its a little trial and error. What we did find was this problem is more evident with aftermarkert piping between the turbo and aircleaner due to the improved airflow versus the stock pipework which is more restrictive.

    In other words, the more you modify your car and improve it, the more likely it is a VTA BOV is going to create a problem.

    Sorry guys for those wanting one, its just one of those things that we may not be able to have. But at least you will pass a visual inspection by the police

  • #2
    At peace with the police, thats my style.

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    • #3
      I'm all about sleeper stylie... Plumb back for me.
      I'd be happier if the zorst could get even quieter with good flow - Hairdresser car with BEEF!

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      • #4
        Oh no, no BOV sound On the flipside, can we get anti-lag instead? :P

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        • #5
          Just get the autobahns induction pipe or similar and ralliart/k&n air filter or pod and with a plumb back you will be able to hear it. Dual ports will still work as mentioned above. Best way to go really cause you can adjust to 50/50 or 100% plumb back when needed.

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          • #6
            I agree - a duel port setup would be the best option if you absoloutly must have a noisy BOV for the sound. otherwise stay with any form of plumback setup

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            • #7
              Yeah its a good thing, noisy BOV's are sooo 2001.

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              • #8
                Very informative, being fairly new to messing about with cars this is awesome knowledge. I got a question though, i have a dual-port BOV, and am wondering, are we saying that the less air getting recirculated the richer the car will run. Does that mean maybe I should just chuck the blankinig plug back on and forego the whoosh?

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                • #9
                  dual port will be fine, You will still have the slight stutter as you may have now.

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                  • #10
                    If you must have the sound

                    http://www.youtube.com/watch?v=Z_fG_b65WiU

                    Season 2 Episode 3
                    BLOWOFF VALVES MYTHBUSTED
                    Will a blow off valve make your car faster? Can you install one on a non-turbo car? How do they work? All these questions answered and a whole lot more

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                    • #11
                      Originally posted by Turbo_Tim View Post
                      Yeah its a good thing, noisy BOV's are sooo 2001.
                      word
                      unless you are 17 and driving a r33 skyline

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                      • #12
                        Ahhhh. Mightycarmods! Nice. No-one gets my shirt. Losers.

                        I used to love the BOV noise until my next door neighbour got his R33 and every morning he'd leave for work with 3 shots from the BOV. Can't stand it now.

                        Just for info sake, a plumb back will have a large input in the base, and a side port for silicone hose, atmospheric will have large input in base, and a side vent (usually with trumpet) and a 50/50 has large base port, smaller side port and atmo port (usually with trumpet) correct? Because that's what the GFB is at Cashies. But it's HUGE! Still improve throttle response. Just have to dial it down a little.

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                        • #13
                          Great information.....also reading rpw modification guide "The most common upgrade is to fit the Mitsubishi EVO Lancer MR Metal unit which is a direct bolt in replacement, although RPW also uses the GFB plumb back model units as well" why would people upgrade? just to change from been plastic to metal?

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                          • #14
                            Originally posted by Satio View Post
                            Great information.....also reading rpw modification guide "The most common upgrade is to fit the Mitsubishi EVO Lancer MR Metal unit which is a direct bolt in replacement, although RPW also uses the GFB plumb back model units as well" why would people upgrade? just to change from been plastic to metal?
                            The plastic one starts leaking at 13-15 psi, the metal evo bypass valves are rated up to 30 psi. Once you start boosting more you need to upgrade.

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                            • #15
                              Originally posted by BFLA View Post
                              The plastic one starts leaking at 13-15 psi...
                              Crap...

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