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Thread: bad flat spots after airbox mod

  
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    yelloperil's Avatar
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    bad flat spots after airbox mod

    I de-restricted my airbox yesterday on my 2.ltr Ecotec Astra Sri however it seems to of just given me realy poor flat spots...

    ie on pulling away if i try and pull away quickly the car feels like its bogging down .........

    is this right>

    what can i go to solve it.....


    Also what FPR do the Turbo engine use?
    MK4 Astra Sri..... <clicky>

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    jayb100's Avatar
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    I have the 1.8 sri and de restricted the air box and had no trouble. If anything has made it alot better as it pulls away so quick now
    Sri 1.8 59k miles dvd/cd player touch screen. Jbl 6x9s and 12" fusion sub in boot.r8 style headlights
    my astra sri

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    jam's Avatar
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    Thats the downside you get with derestricting I'm affraid. Its to do with air flow within the pipes.

    If the car is travelling at 4000rpm the air will be flowing through the pipe with ease. Now you come to a stop so your car is now at idle IE 750rpm. The air now is still rushing inwards at the same speed as if you were doing 4000rpm. But obviously only using a fraction of the air means the pipe/airbox gets full of air very quickly. This leads to the air stalling IE almost coming to rest inside the airbox. Now you start to take off again from the lights, the air draw from the engine is bigger but because the air is virtually at a standstill it really struggles to speed up the air to get it into the engine quick enough (flat spot). As the vacuum is created by the air being used by the engine the once relatively still air is now speeding up flowing fast and faster to supply the engine with air.

    So basically what you'll find is a flat spot at take off, but what you gain is greater efficiency at mid-high revs and effectively more brake horse power.

    Hope this explains a bit. Its very simplified but I hope you get the gist of whats happening?

    jam
    Its a jam thing

    Haec credam a deo pio, a deo justo, a deo scito?



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    cnkh's Avatar
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    Jam thats a good read i did not know that.

    Ive derestricted my airbox on my z18xe and did wounder if it was me thinking it was a tad unresponsive (and i mean a tad) at low revs.

    Overall though i do think de-restricting the air box has helped more than hinderd.

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    I've not done this yet, but i find it to be quite poor at very low revs on a standard car (1.. I can see how some would disagree though as i'm being quite critical with that comment. By no means is it a slug, i just expected more.

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    Providing you can live with giving it a little more gas on take off then its worth it. I love the way it had transformed my car through the mid-high rev range. I can live with it bogging down a little on launch. Overall everyone has got to try the mod. (BTW it'll be the fitting of a vectra C intake pipe over the standard pipe that will cause 99% of this lag). If you look at your old pipe it has 'resonance chambers' which for a simple term gives the air somewhere else to fill up and will also help with the lag.

    jam
    Its a jam thing

    Haec credam a deo pio, a deo justo, a deo scito?



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    SXT's Avatar
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    i noticed mine bogged down alot... and i got hacked off with it. It got to the point with full throttle from stand still would almost stall the car, and thats after sat stationary for 2 mins

    found a really cheap viper induction kit on ebay bought that, bodged it on and now its fantastic. i will never consider putting the airbox back on again, unless i sell the car

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    Is that accurate Jam? The resonance box on the Z16/Z18XE engines is right on the throttle body, there are no resonance parts on the airbox or intake pipe?

    I know what you're on about - air flow speed is lower once the derestriction is done and the Vectra pipe is fitted, same goes for fitting a straight through catback...

    Does the 2Litre have an airflow metre? There's also the air temp sensor which if knocked off when you do this mod can cause a few weird problems too...is everything definetely connected back where it was before the mod?

    These engines have poor torque lower down regardless of these mods, but the airbox/intake pipe mods alongside the catback systems can add noticeable bhp and torque over the OEM figures or at least it did for me, the car is no way worse than before and I've never noticed this hesitation once the mods were done, if anything the engine picks up much easier with less lag on the throtte...

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    Quote Originally Posted by nry View Post
    These engines have poor torque lower down regardless of these mods,
    Quote Originally Posted by nry View Post
    I've never noticed this hesitation once the mods were done, if anything the engine picks up much easier with less lag on the throtte...
    I can totally agree with that 1st comment from experience

    I'd done a fair bit of reading (as i usually do) before i bought the relevant parts & i'd not come across this before tbh (lag). Not saying anyone is right or wrong, just that this is the 1st i've read of it related to this mod.

  10. #10
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    The box near the throttle body is an air expansion chamber allowing that to fill first to help keep the speed of the intake piping up. This also helps at peak demand IE full throttle. The resonance chamber is attached to the intake pipe itself.

    jam
    Its a jam thing

    Haec credam a deo pio, a deo justo, a deo scito?



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