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Thread: air box mod....

  1. #1
    Regular Member david.aka.judas's Avatar
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    Default air box mod....

    now, before I explain myself, please understand that I'm not trolling on a late/ early friday/ sat.....

    ok, here goes.....

    I want someone to explain why the air box mod makes any difference. this is my view....

    the plastic piece that sits in the bottom of the air box is specifically designed to increase the speed of the air going through the filter. I understand that this make the filter dirty in one spot but that only proves my point.

    I understand that you have to make sure that the filter is clean.

    by taking the piece out you increase the volume of air going into the box but you also reduce the velocity, making it harder for the air to go through the filter, a classic case of Bernoulli's principle (but air not fluid), has anyone done a before and after dyno to show the difference?

    whats your thoughts please???
    Last edited by david.aka.judas; 20th November 2010 at 01:45.

  2. #2
    Regular Member rushy's Avatar
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    Vehicle : SRi


    Engine : Z22SE (2.2 Petrol)

    Year : 2004

    Mileage : 137000

    Default

    I cant see how it speeds it up. The velocity might be faster at the point it vents into the box but not going through the filter. From my understanding its only there to help suppress noise. I don't actually believe it makes any difference to performance as the air is sucked in not forced. The speed of the flow into the TB is more affected by the length and bore of the pipe from the air box to the TB and its this length and size that is sometimes tuned on some cars (especially important on NA) to work in balance with the shuttle affect of each draw/downward stroke of the piston.

    With things like this I always find you notice the real affects when you go back to stock, the same as when you put an open cone filter on. You think its better but its only the sound that tricks you into it, its not until you go back to a sealed filter that you realise the cone is actually worse.
    Last edited by rushy; 20th November 2010 at 01:58. Reason: I spell like a 6 year old

  3. #3
    Regular Member david.aka.judas's Avatar
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    Default

    thanks rushy for the reply.

    it speeds the air up because the trumpet narrows. its like placing your finger over a runnig hose, the velocity increases but the volume decreases.

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    Vehicle : Golf 7

    Trim : GTD

    Engine : 2.0 TDI 184PS

    Year : 2014

    Mileage : 40000

    Default

    Removing it effectively removes a 'pressure drop' in the airbox. This however, granted is very slight but lets the engine breathe easier as it doesn't waste HP in moving air through a narrower gap.

    The piece of plastic is there to not increase flow rate of the air but make the flow smoother and focus it through the air box properly.

    Gazza4

  5. #5
    Regular Member Chocki's Avatar
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    I'd be more inclined to think that the additional plastic piece is there to stop objects perforating the filter, have you seen what your car hoovers up into the air intake!, if you lived in an area with lots of pine trees, the stiff needles could perforate the air filter so this plastic piece deflects them towards the side of the air box where they drop out of the air stream and collect in that recess over that end of the box.

    It's only speculation on my part but does sound sensible!.

    I've removed this piece in my car tens of thousands of miles ago without any detrimental effects or noticeable performance increases by removing it so it may as well have stayed there.

    Your better off just changing the air filter every 10k miles instead of the recommended 20k as this will have more impact than removing this piece of plastic.

  6. #6
    Regular Member Chocki's Avatar
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    Oh one thing I have found is that the screws holding the air box together can strip their threads easily or rather the muppets at the dealers are too heavy handed!. What I ended up doing on mine was drilling out the hole to 6mm and pushing a rawl plug in of the necessary size then screwing the lid back down.
    In 10k miles when I change the filters again, I'll just push new rawl plugs into the holes and screw down again. Cheap fix.

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    I think the only reason that opel design this airbox like it is, is for the sound.
    When you don't have a "trompet" into the airbox you are getting sound virbations what you can hear outside.

  8. #8
    Regular Member Derek Mc's Avatar
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    I also believe the purpose of the trumpet was for drive by noise and removal of the trumpet is for the benefit, due to full usage of the swept volume of the airbox as the current design cuts the area in about half that is used for filtration. Just my opinion however.

  9. #9
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    Quote Originally Posted by david.aka.judas View Post
    thanks rushy for the reply.

    it speeds the air up because the trumpet narrows. .
    I dont understand what you mean by narrows, look at the pictures in how2 air box mod, it starts at 73 mm, (inside measurment) and at the point where it flares its 88 mill thats getting wider like a trumpet not had the car on a dyno, but after 10,000 miles of NO TRUMPET, I put it back in, straight away the flat spot was back and engine did not feel as smooth to drive, and a long M-WAY run (300 miles) mpg droped by 3.8 mpg, so I took it out.

  10. #10
    Regular Member david.aka.judas's Avatar
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    thanks for the replies. we need to have a collection so someone can have 2 dyno runs - one before and one after...

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