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    Default Vented hoods ?

    what are your guys' take on a vented hood.
    I have read on there that you want air to enter the engine bay thought the front of the radiator and exit as designed by the manufacturer, I am guessing somewhere thought the bottom.

    I am thinking of not running the bottom cover on my car (although I have also read that, that is not a good idea), and also replacing the factory Alum. and steel hood for a carbon hood with vents.
    I several GT cars / race cars have vented hood so they must do good?

    Thanks in advance,

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    Chest hair required Olitho's Avatar
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    I am using these - Home page

    It is important to know the low pressure areas on the hood so you can maximize vacuum. The vacuum on most cars should improve front grip and draw even more air through the radiator.
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    Yes, TrackSpec louvers are solid. A lot of Subaru BRZ / Toyota GT86 time attackers (86CUP, GTA, etc...) run the TrackSpec hood vents too.

    Specifically to the BRZ / 86, the vents reduce front lift, which basically gives you more front grip at speed, enough to balance out a small wing without having to use a fragile front lip or splitter. The effect is very noticeable when doing a back to back test between regular and vented hood on the same track day.

    Naturally, the vents also help with cooling.

    Keep in mind that some of the cheaper aftermarket "carbon" hoods are heavier than the equivalent OEM aluminum hood + trackspec vents combo
    Last edited by JulioG; 04-02-2018 at 08:14 AM.

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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by JulioG View Post
    Keep in mind that some of the cheaper aftermarket "carbon" hoods are heavier than the equivalent OEM aluminum hood + trackspec vents combo
    I think that is because they are really fiberglass hoods with a carbon fiber overlay for looks. They are not 100% carbon fiber. In the Corvette world there is a company that sells carbon fiber fenders, but in truth only the last layer is carbon fiber so there is no real weight savings.

    So watch out for what you buy.
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    Quote Originally Posted by FoxSTI View Post
    what are your guys' take on a vented hood.
    I have read on there that you want air to enter the engine bay thought the front of the radiator and exit as designed by the manufacturer, I am guessing somewhere thought the bottom.

    I am thinking of not running the bottom cover on my car (although I have also read that, that is not a good idea), and also replacing the factory Alum. and steel hood for a carbon hood with vents.
    I several GT cars / race cars have vented hood so they must do good?

    Thanks in advance,
    What kind of car?

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    Quote Originally Posted by Olitho View Post
    I am using these - Home page

    It is important to know the low pressure areas on the hood so you can maximize vacuum. The vacuum on most cars should improve front grip and draw even more air through the radiator.
    Without having a wind tunnel.. what is the next best way to figure out the low pressure areas under the hood ?

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    Quote Originally Posted by Olitho View Post
    I think that is because they are really fiberglass hoods with a carbon fiber overlay for looks. They are not 100% carbon fiber. In the Corvette world there is a company that sells carbon fiber fenders, but in truth only the last layer is carbon fiber so there is no real weight savings.

    So watch out for what you buy.
    I was looking at a SEIBON carbon hood, but in asking them, they told me the use a process called carbon infusion and in some items the backing is fiberglass.
    They say their hood weighs 20 lbs. which is close to what my OEM hood weighs.

    I am more interested in the vents at this point since there is really not weight savings.

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    2015 Subaru STI

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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by FoxSTI View Post
    Without having a wind tunnel.. what is the next best way to figure out the low pressure areas under the hood ?
    For the Corvettes it is possible to find CFD information online. Computational Fluid Dynamics and the Corvette?

    For your STi I suggest you talk to Trackspec Motorsports as they have done that research.
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    Quote Originally Posted by Olitho View Post
    For the Corvettes it is possible to find CFD information online. Computational Fluid Dynamics and the Corvette?

    For your STi I suggest you talk to Trackspec Motorsports as they have done that research.
    I will thank you,

    speaking of keep the air flowing, I see several people remove their wheel fender liners. What is up with that, just like removing the bottom the engine cover, doesn't that also disrupt the air and causes lift?

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    Quote Originally Posted by FoxSTI View Post
    I will thank you,

    speaking of keep the air flowing, I see several people remove their wheel fender liners. What is up with that, just like removing the bottom the engine cover, doesn't that also disrupt the air and causes lift?
    wheel well is a high pressure area. not sure why people remove wheel fender liners (my guess is for tire clearance), but many do put vents top (don't have to be top, but in theory it helps with downforce even more) of fender to vent out the pressure.
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    Quote Originally Posted by FoxSTI View Post
    I am thinking of not running the bottom cover on my car (although I have also read that, that is not a good idea),,
    no, that's definitely not a good idea... bottom cover keeps engine bay at lower pressure......
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    That explains why some of the DTM and LMP cars have vents right on top of wheels.
    Where can i read more about these hight anf low pressure zones.

    Btw, i just removed the fire retarter blanket from under my factory hood only to discover some bracing in the way of where i would cut the vent opening. Ill pos a photo soon
    Maybe it wont be a big deal tonjust cut through it.

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    Aren't hood vents just drag? I think less is more unless you have no other way to reject the heat.

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    Quote Originally Posted by fatbillybob View Post
    Aren't hood vents just drag? I think less is more unless you have no other way to reject the heat.
    STI needs all the help it needs. I wonder why nobody has told op to sell there STI, because they all go kaboom ?
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    Quote Originally Posted by fatbillybob View Post
    Aren't hood vents just drag? I think less is more unless you have no other way to reject the heat.
    Well.. I have always wanted to be a queen, heyyy.. LOL. Sorry for the bad* joke couldn't resist. Happy Tuesday.
    Last edited by FoxSTI; 04-03-2018 at 10:56 AM.
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    The hood blanket may be to keep the hood from getting too hot from turbo which might cause paint damage, so you may want to put it back if you cut the hood for vents.

    There's a couple entry level books on race car aerodynamics that you can get, links below. Both cover the same basic topics (in agreement) so really you only need one. IIRC McBeaths covers a little more CFD and Katz's has more math if you're a math guy.

    Willem Toet, a former F1 aero guru has a number of articles here you may find informative. https://www.linkedin.com/in/willemto...ctivity/posts/ He's written quite a few articles so scroll down through them to find ones on diffusers, ducts, wings, etc.

    https://www.amazon.com/Competition-C...GTGF4KBREJ3DJ3

    https://www.amazon.com/Race-Car-Aero.../dp/0837601428
    Last edited by NOT A TA; 04-03-2018 at 10:54 AM.
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    Quote Originally Posted by bellwilliam View Post
    STI needs all the help it needs. I wonder why nobody has told op to sell there STI, because they all go kaboom ?
    Oh yes, this is true. You tell the car "tomorrow its track day" and it starts to overheat in your garage with the engine off. - BTW I took care of those issues. But yes I want more cooling help.

    Here is the photo I promised guys.
    Below is what I would need to cut to make this work. I want the vents closed to the edge and not in the center close to the inter cooler opening.

    hood-vents_sti.png
    Last edited by FoxSTI; 04-03-2018 at 11:19 AM.

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    If you think cutting the under hood supports will ruin the structure, you could just cut the skin material and then swiss cheese the supports with a hole saw and drill bits.
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    Quote Originally Posted by b3d3g1 View Post
    If you think cutting the under hood supports will ruin the structure, you could just cut the skin material and then swiss cheese the supports with a hole saw and drill bits.
    That is a great idea. That actually allows me to put the vents anywhere I want.
    I have seen some people use jigsaw to cut their hoods and some other use a rotary tool. What do you guys recommend?

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