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  1. #1
    VXRed blooded Andyb712's Avatar
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    28th July 2018
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    Default Rear bcs bypass wow just wow

    Just did the bypass on mine the other day cannot believe the difference it's made so much better especially in 2nd gear but can still notice it even in 1st

    Been chasing a boost issue for a while and the difference is now night and day

    Boost is just so much smoother now it pulls sooner longer and harder in every gear

    But I'm of the belief same as adam, rabbid, percy and many other's that the rear bcs and vacuum box is there for a reason but i did not want to change the bcs and vacuum box if there was nothing wrong them wasting unnecessary cash if it was not needed

    I have a feeling it's the vacuum box that's failed on mine rather than the bcs but I'm just going to replace them both to be sure then hook it all back up and see how it goes once I get the new vacuum box and bcs

    Seen so many posts saying do it and just as many saying don't do the bypass

    But me personally I reckon it's worth doing it just to see if the vacuum box and bcs are faulty

    Most people say you just feel it in 1st and 2nd but for me at least it's a major improvement in ever gear it even seems better in between gear changes too like the boost is ready to go again a lot sooner than before hand on each up shift

    Its like a 5 min job and takes 5 min to put back to original it can all be done from the top of the engine bay and you don't even have to go underneath a lot of the threads about it make it seem a lot more complicated than it actually is

    You don't need to touch the bcs or vaccum box just to do the bypass test obviously if your doing the bypass permanently you would eg removing the OE vacuum box and OE vacuum lines but if your just doing a temporary test to check for the fault you can leave it all hooked up

    As has been stated previously on here though if you get a big improvement you clearly have a problem with the vacuum box and or rear bcs

    So me personally I think the bypass is a good thing to try at least to diagnose the issue
    Last edited by Andyb712; Today at 02:02 AM.
    2009 Astra H Vxr arden blue uprated gearbox endcase with bigger bearings, 3" cobra catback non res with toyosport 2.5 double decat, mtc crossover delete and tophat

    Planning to go stage 3/3.5 eventually

  2. #2
    VXRed blooded Andyb712's Avatar
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    Just a small update fitted the new vacuum box and rear bcs today

    And just as the bypass told me they were both definitely worn slightly less boost in 1st and 2nd but 3rd 4th 5th and 6th now feel just as good as running the bypass

    So the bypass is definitely a worthwhile test imo
    2009 Astra H Vxr arden blue uprated gearbox endcase with bigger bearings, 3" cobra catback non res with toyosport 2.5 double decat, mtc crossover delete and tophat

    Planning to go stage 3/3.5 eventually

  3. #3
    VXRed
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    Seems like a good way to see/solve if there's an issue for sure. Did you follow a diagram to run the BCS bypass? Only reason I'm asking is because I brought mine and the previous only must of done the BCS bypass and I want to put back to standard but can't find a picture/diagram to follow.

  4. #4
    VXRed blooded Andyb712's Avatar
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    Nah mate I just used a bit of common sense

    One pipe from recirculation valve to the left side of the throttle body and then a tee piece for the fpr

    But trying to put it back standard If you didn't do the bypass may be more difficult especially if the previous owner took all the old system out

    Its even more complicated if your trying to figure out someone else's work if you have a boost guage or dump valve involved as there will be even more tee pieces and vacuum lines involved

    My post is more aimed at helping people diagnose issues with the stock standard OE setup
    Last edited by Andyb712; 20th March 2019 at 03:24 PM.
    2009 Astra H Vxr arden blue uprated gearbox endcase with bigger bearings, 3" cobra catback non res with toyosport 2.5 double decat, mtc crossover delete and tophat

    Planning to go stage 3/3.5 eventually

  5. #5
    VXRed blooded Rksmith's Avatar
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    15th December 2016
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    There you go mate standard system


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