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Automotive Restriction of air within enclosed space when intake snorkel pulls in air

  1. Jun 4, 2012 #1
    Restriction of air within enclosed space at intake snorkel - pictures added

    I have a modified intake pipe in my engine bay. It is 3 inches in diameter, mounted horizontally from the airbox and the mouth of the pipe (where the air gets sucked in) is located VERY CLOSE to the headlights, approximately about 2 centimetres away from the headlight housing. When the hood is closed, it leaves about 1 centimetre of space above the intake pipe.

    From the scenario above, would the positioning of the said pipe and limited space between the mouth and the housing be restrictive when the pipe pulls in air? If so, how much should the pipe be shortened to ensure that it can suck in air without any restriction from the enclosed space?

    The intake pipe was changed to a bigger diameter to reduce restriction when the engine pulls in air, but as I shorten the pipe the engine pulls in hotter air as it is closer to the engine block. Is there an optimum size on how much the pipe could be shortened?

    edit - few pictures to illustrate my point. sorry if I didn't explain it well.

    An overview. the gold pipe is the said 3inch pipe.

    Close up. This shows how close the mouth of the pipe is to the headlights which may impede air flow.

    Hand was a little shaky with this one, but it's another angle of it.
    Last edited: Jun 4, 2012
  2. jcsd
  3. Jun 4, 2012 #2

    Ranger Mike

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    and welcome
    can you send photo or sketch??
  4. Jun 4, 2012 #3
    Added photos to illustrate. Thank you for helping out :)
  5. Jun 4, 2012 #4


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    This is one way to look at it: The cross section of a 3in diam pipe is about 7 square inches.

    The "gap" between the headlights and the pipe is roughly a cylinder with circumference 3 pi inches and "height" 2/2.54 inches, so the area for the air to get in is about 6 square inches. So it may be creating a bit of flow restriction, plus the fact that the flow may have to turn through 90 degrees to get into the pipe.

    Whether that actually matters, compared with the airflow between the other end of the pipe and the cylinders, is another question though.

    A cheap way to find out would be to make the situation worse by putting a sleeve on the pipe to make it a bit longer, and see if you get worse engine performance. If not, there's nothing to worry about.
  6. Jun 4, 2012 #5
    Hi AlephZero,

    Thanks for your input.

    My goal here is to reduce as much restriction as possible at the snorkel when the engine pulls in air, mainly to improve fuel consumption (less pumping losses) and possibly better performance (more airflow). Of course there's also other characteristics that may have to be considered:

    1. The engine has a cubic capacity of 1.5L,
    2. This car is a daily ride to the office and shops, thus the car does not drive around at redline, thus does not pull in much air as it actually needs, and
    3. The throttle plate (probably the last area of restriction before the intake manifold) is 2.5 inches.

    In this case, I am assuming that:

    1. The 3 inch pipe will never be 'saturated' with airflow, as the throttle plate has a diameter of 2.5inch, and
    2. Restriction only happens at the gap area when the car's engine approaches redline.

    Now what I want to do is to cater for every situation - I want to shorten the pipe to reduce the restriction, but only shortening it enough so it does not bring the mouth closer to the engine block where hot air resides. I could route an elbow pipe to the front grille to take advantage of the ram air effect, but:

    1. There is no opening at the area where I can route the pipe to scoop in air from the outside,
    2. More bends in the pipe means more turbulence which in the end results in restriction,
    3. I live in a tropical area, where rain and dust is very prevalent.

    Also, about the sleeve thing - I guess you mean something like this?


    Another problem is that I can't actually measure performance - dyno runs are a luxury from where I live, I don't trust butt dynos - so as an alternative I measure my average fuel consumption when the car reports near to empty. Not too accurate but at least I have an idea - what I'm just afraid that the improvements would be so close to the margin of error that I wouldn't be able to notice it.

    To make things simpler, let's assume that the maximum amount of air the engine can pull in is from its most restrictive point, which is 2.5 inches. In this case, how much gap should I leave from the mouth of the pipe, all other factors equal?
  7. Jun 5, 2012 #6

    Ranger Mike

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    Al-zero is spot on..is there any way you can plumb to outside air? Cut a hole in the grille?
  8. Jun 5, 2012 #7
    Not really willing to as it's a new car and I'm not planning to perform any irreversible modifications. :(
  9. Jun 6, 2012 #8
    Temperature of air taken in is the big issue.
  10. Jun 6, 2012 #9
    It is - which is why I'm trying to strike a balance between the length and space.
  11. Jun 8, 2012 #10
    Get on the car forums, plenty of designs out there for airboxes, you're not gonna see any significant results with that pipe.

    Being that close will hinder the incoming air but nothing that you will notice.

    Here's something I made myself a while back, gives you some idea of the air going into the runners.

  12. Jun 8, 2012 #11
    Thanks kazx9r, but what do you call this process? Is it to measure air pressure/density?
  13. Jun 8, 2012 #12
    I have the intake pressure in another analysis, this one is to analyze inlet outlet velocity, you want maximum velocity which requires a longer pipe or pressure which you don't have.
    There are some video on youtube people using 10foot intake pipes gaining a good amount of power, obviously its only for demonstration.
  14. Jun 9, 2012 #13
    So if one has a mid-engine or rear-engine car would it be ideal to run the intake tube to the front of the car?
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