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Thread: Vehicle speed effect in IAT

  1. #41

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    Compared bonnets yesterday. The rear part where it attaches to the pillar is taller in this area. Same as the MPS 6 pictured a few posts back.

  2. #42
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    The results are exactly as expected. This photo was taken at 110 kmh.




    Mal some great notes, man I which I had this much spare time.. Great work though.....

  3. #43
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    Re-amemiya vented bonnet has the vents just forward of where that left hand string is spearing off to the side....possibly (probably?) good spot to vent from?

  4. #44

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    I agree Nexus; even had a look at the structure underneath to see how doable it is. If there was an OEM looking vent that could be placed in that area I think it would do a lot to help increase airflow through the engine bay and TMIC.

    Wasted a lot of time yesterday on trying to video the airflow behind the bumper and around the intake but it's too tight and I just couldn't get a camera angle that showed anything useful. Shame really because I think are some gains to be made by getting a better understanding of how the air is behaving around the intake. The other problem was light: it's pitch black inside the engine bay when the bonnet is down and I couldn't get enough light in there to make the camera happy.

    I've got one more test to do with the rubber strip removed from the rear of the bonnet.

    Gone to Volvo


  5. #45
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    Just a little question to help get my head around this.

    The thoughts here is to remove heat and/or draw cooler air to the TMIC, correct?

    My thoughts are, if you were to set up some form of ducting to the TMIC from the rear of the bonnet would the fact that air is being drawn from the front through the standard intake possibly cancel that out as the air flow would travel straight through?
    Thought number two - and form of bonnet venting would have little if any effect on intercooler temps as the cooler is mostly blocked off because of the box under the bonnet

    At speed, it "might" be better to draw air from the windscreen and not from the front, but at low speed, drawing air from the front would be the better option, both i dont think would work, so in real world conditions, drawing from the front would be the best comprimise

  6. #46
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    I thought the high pressure holds the strings in place and flowing in the direction of the pressure and the low pressure allow it to flap about

  7. #47

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    I agree that ducting air from the front is the best compromise. But since this discussion started with what appeared to be a damming effect inside the engine bay and a lack of outflow capacity at speed, I believe the duct becomes somewhat ineffective because air will stop flowing into it if it can't get out after passing through the TMIC.

    Bonnet vents would allow the release of the high pressure (stagnant) air that builds up in the engine bay, and being exposed to the low pressure air flowing over the bonnet the hot air would be literally sucked out of the engine bay by the pressure gradient.

    By releasing the downstream blockage in this way, I believe we could significantly increase the volume of air flowing through the TMIC. The other potential benefit of increasing the volume of air flowing through the engine bay would be cooler air entering the engine intake.

    I recall that the early WRX had bonnet vents that were blocked off. But Subaru intelligently made it very easy for owners to remove a couple of screws and remove the blocking plates. They worked extremely well when opened up, you could see the hot air pouring up through the open vents. And they made a noticeable difference to performance, presumably for the same reasons we're discussing, ie TMIC and intake air flow.

    I would want to do some more testing with a manometer to confirm my suspicions, but I'm almost convinced that cutting a couple of holes in the bonnet would be a very worthwhile performance mod for people running a TMIC and SRI.

    Gone to Volvo


  8. #48
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    I understand what your saying mal and agree.
    My guess the most effective method would be ducting under the cooler to the rear of the bonnet to possibly allow more air to travel threw the cooler.

    My GTi-R pulsar with a mildly modified SR20 turbo (0-100kmh in 5.4 seconds without dropping the clutch) had similar venting to the WRX, blocked off at factory, but easily removed. After a bit of normal daily driving you could feel and see plenty of hot air exiting when you park it. But I couldn't notice any performance difference.

    Race scenarios however might find different results

    I wonder what tests Mazda did, what results they found and why they settled with what they did?

  9. #49
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    Default Heat at TMIC

    Result from Apollo Road run - yes it does get hot at the intercooler.

    Photo's of the badge from intercooler surround, painted black previously because the heat cracked the chrome.
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  10. #50

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    Kypros (toxicMPS) had the same problem with chrome peeling off a melted badge. Interesting that not all cars are affected the same way.

  11. #51

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    awesome work on the aero testing,


    autospeed.com have heaps of articles about this kind of stuff and is definitely worth your while to read it

  12. #52

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    I’m no expert but it seems to me that it is low pressure at the base of the windscreen, possibly with high pressure above the low pressure, I just cant see how its high pressure when one of the pieces of string aren’t even moving.

    If you gave the high pressure area above that low pressure area some air to suck out (such as removing the rubber strip at the back of the bonnet) it would then suck out the air from the engine bay both removing the heat and improving air flow over the car, so the faster you go the more it sucks out and the cooler it will be and you will also lose this low pressure (drag) area.

    *Disclaimer* lol,

    Of course I’ve got no technical experience in this field so I could be 100% wrong, this is just how I see it

  13. #53

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    check out autospeed pockets, very informative and very in depth to explain the wool tufts...

    i imagine putting vortex generators on the trailing edge of the roof would bring good aero gains... you need to improve flow through the engine bay by low pressure, you think that changing the bottom of the engine bay would give you this flow ?

  14. #54

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    The critical issue is that we are talking about static pressure at the surface, not dynamic pressure. I don't think it will help anyone if we complicate the discussion any more than it already is.

    It is counter intuitive to a lot of people, but trust me, it's high pressure at the base of the windscreen. It would seem to make sense that opening the rear of the bonnet would create a flow-through from front to rear, but often the opposite happens because of the high pressure zone. Have another read of the pilot text that I posted earlier.

    You can see it already in the photo, look at the tufts in the red circles, they are being sucked INTO the engine bay at high speed. I'm going to remove the seal and try it again. I could be wrong, but expect I'll get the same result.

    The current situation appears to be that the only exit path for air entering the engine bay is the engine intake or along the floor pan.

    Gone to Volvo


  15. #55

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    generally by modifying the floor pan, you can achieve what your trying to do.. increase airflow through the engine bay ?

    this link is especially helpfull

    and the followup


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