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Thread: Bonnet Spacers

  
  1. #1
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    MarkySRi's Avatar
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    Bonnet Spacers

    Im looking to fit bonnet risers to lift the back end of my bonnet up to aid airflow and i think they look gd.

    any chance that any1 has done this before and is it just a case of gettin some steel blocks cut to size and extend the bolts thro to the bonnet and hinge?

    also im guessing the bonnet catch wouldnt line up properly so a set of bonnet pins would be needed.am i correct?

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    They do not aid airflow, they impede it. Air flow occurs only when there is a difference between pressures. Air will flow from a region of high pressure to one of low pressure: the bigger the difference, the faster the flow.

    You have a high pressure area at the rear of your bonnet and a high pressure in front of your front bumper. You have a low pressure area inside your engine bay. Now the most use the air can be to you is in cooling hence the use of a radiator, intercooler etc at the front of the engine bay behind the front bumper. So you want to keep the engine bay as low a pressure as possible whilst retaining as high pressure as possible in front of your front bumper (hence large airdams on front bumpers etc.) so the air will flow through the grilles on the front of the car and into the engine bay then out the back of the bay under the car following the largest pressure differentials. If you open up the back of your bonnet (where the highest air pressure on the whole body of the car is!) you will draw air into the engine bay at the rear and begin to equalise the pressure differential between the engine bay and the front of the car - thus inhibiting air flow through your rad and intercooler etc.
    I hope this helps mate. It may look good but its CRAP for airflow!

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    MarkySRi's Avatar
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    if thats rite then surely bonnet vent have the same effect?

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    dangerstevie's Avatar
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    The following link will take you to a thread on a volvo forum where exactly the same questions were raised and i gave the same answers with links to more info on the aerodynamics too.

    http://www.vpcuk.org/forums/showthread.php?t=19578

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    i had the bonnet rasied on my metro gti. it made a difference to under bonnet temperatures, you could see the heat coming out of the rasied bit at the back? i dont see why it would be a problem. im obviously not clued up tho?
    www.chilled-rc.net For all your RC car/boat/heli/plane needs

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    I dont disagree that when stationary it will allow heat out but its more important to get heat out of the motor when driving hence the importance of the airflow.
    If you have a look at the diagram on that link hopefully it will explain things a little clearer.

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    andys sri-t's Avatar
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    this mod a common on escort and fiesta turbos and you can see the heat haze pour out
    never drink and drive .you might spill your drink
    **** n/a turbo is the way

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    Just because its common does not mean its beneficial when the car is moving. You can only see the heat escaping when the car is stationary. The laws of aerodynamics prove this "modification" is not beneficial to cooling when the car is in motion.

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    lee gsi's Avatar
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    How many race cars do you see with the back of the bonnet raised?
    The truth is always the truth even if you haven't realised it yet...

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