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Old 08-10-2012, 09:06 PM   #1
djc1827
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Default Running a hood scoop grill necessary?

I am running a hood scoop grill since I am running a fmic and I am wondering if the under the hood temps would be lower without it on? I was told I should run one due to aerodynamics and the air coming in isn't entering the tmic which forces tons of air against the firewall....someone said it could cause the front end of the car to lift at high speeds or slow you down. Has anyone done testing on this?
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Old 08-11-2012, 02:29 PM   #2
wrxdrvr
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Don't know about enough air getting in from the scoop to cause lift, but it certainly does/can "pressurize" the under-hood area and can make it harder for air to enter from the front area and may reduce FMIC and radiator efficiency...So for a car with a FMIC I would block off the hood scoop.
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Old 08-11-2012, 08:16 PM   #3
djc1827
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But then your keeping in tons of heat thus raising intake temps...at least with the grill the heat escapes. If removing the grill doesn't effect aerodynamics I think you would only gain hp with cooler temps. After heatsoaking at a light for one minute I have seen my intake temps that are usually 15-20 degrees warmer for example. Its 70 outside. My intake temp is 85-90 crusing. It could go to 120-130 at a light. Even 150 after 3 minutes. It would then take 3-5 mins to cool back down to 85-90 once cruising at 40-55mph. With the grill off, you will increase air flow and release heat 50% faster possibly cutting the time in half. Less knock more timing(hp) I will run a test on this when my engine is back together. I think a hood with several grills or holes would run faster than a hood scoop delete/block off or impreza hood
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Old 08-11-2012, 09:30 PM   #4
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some research was done by autospeed a while back on forward facing hood scoops and they actually found that at high speeds, airflow will reverse and flow out of the hoodscoop instead of into it.

basically i am saying that i highly doubt that the airflow into the engine bay will cause enough pressure to actually cause the front end to lift because there really isn't that much air hitting the firewall anyways.

even if there was a significant amount of airflow in there, the low pressure underneath and over the vehicle would cause the higher pressure air in the engine bay to flow down the backside of the engine, around the bellhousing, and out the bottom of the engine bay or out the hood scoop anyways.

in a nutshell, my opinion is that the decrease in downforce is going to be very trivial...at least at the speeds you will be going on the road or drag strip.
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Old 08-11-2012, 11:06 PM   #5
djc1827
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So it would only help me by taking off the hood scoop grill then? Exactly what I thought, heat would leave the engine bay easier. I was even thinking about manually wiring up the fan to run on a toggle switch like I did on my talon or seeing if someone would make me a custom carbon fiber hood with many holes and grills so I would never heat soak while stopped in traffic. I am using a turbo blanket and I am also have my fmic and pipes coated this time. I am still running cobb short ram intake tho
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Old 08-11-2012, 11:24 PM   #6
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well, the short ram is more or less just increasing your intake temps and your pre-intercooler temps, but heatsoak is actually increasing your post intercooler temps which matters WAY more. obviously, sucking colder air to begin with is a plus, but it isn't doing much in terms of heatsoak or underhood temps.

also, you have to be careful with how much you modify things because your oem hood has been fairly thoroughly thought through in terms of aerodynamics, but if you start putting a bunch of holes in that, you are going to start significantly increasing the parasitic drag of the vehicle (this effect is going to increase as speed goes up). not only that, but you also run the risk of decreasing pressure in places to a point where it actually completely changes the original design of the airflow through and over the vehicle.

basically, just be really careful not to do so much that you throw things off too much because this can possibly have negative effects on handling, performance, and economy.
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Old 08-12-2012, 06:40 PM   #7
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Quote:
Originally Posted by djc1827 View Post
But then your keeping in tons of heat thus raising intake temps...at least with the grill the heat escapes. If removing the grill doesn't effect aerodynamics I think you would only gain hp with cooler temps. After heatsoaking at a light for one minute I have seen my intake temps that are usually 15-20 degrees warmer for example. Its 70 outside. My intake temp is 85-90 crusing. It could go to 120-130 at a light. Even 150 after 3 minutes. It would then take 3-5 mins to cool back down to 85-90 once cruising at 40-55mph. With the grill off, you will increase air flow and release heat 50% faster possibly cutting the time in half. Less knock more timing(hp) I will run a test on this when my engine is back together. I think a hood with several grills or holes would run faster than a hood scoop delete/block off or impreza hood
He has a FMIC...

Quote:
Originally Posted by djc1827 View Post
So it would only help me by taking off the hood scoop grill then? Exactly what I thought, heat would leave the engine bay easier. I was even thinking about manually wiring up the fan to run on a toggle switch like I did on my talon or seeing if someone would make me a custom carbon fiber hood with many holes and grills so I would never heat soak while stopped in traffic. I am using a turbo blanket and I am also have my fmic and pipes coated this time. I am still running cobb short ram intake tho
You have a FMIC... Thus no real heat-soak like a TMIC... As for the scoop you would be better off without a scoop or a blocked off scoop (with the grill) like you have now.. As for the holes in the hood (vents) you need them in the front part of the hood, like mine for the best results in "sucking" out the hot under hood air and allowing in more cold air through the FMIC and radiator... http://s18.photobucket.com/albums/b1...t=IMG_0595.jpg
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Old 08-12-2012, 09:56 PM   #8
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Very nice man, where did you buy the vents and I know some body shop guys so...just wondering if it would be cheaper to buy carbon fiber hood with vents and sell my oem hood
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Old 08-13-2012, 12:35 AM   #9
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I made the vents myself after a lot of testing for the best location/effect, it's on the stock hood... With everything I did, I have elliminated heat-soak of the TMIC and made my TMIC efficiency 86%, a much better number than the stock set up of 60%...
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Old 08-13-2012, 05:39 AM   #10
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i made a thread similiar to this a while back. the KS tech grills actually STILL have air flow into them at high speeds (kstech guy posted in my thread). the only way to actually vent out the hole in the hood is to run a reverse scoop like the following: http://www.ebay.com.au/itm/2002-03-W...item335de54b15

now i know that's for an 04/05 but you either need to find something similiar or go get yourself an N/A bonnet. i'm sure some ricer would GLADLY swap you one.

Last edited by vicious_fishes; 08-13-2012 at 05:45 AM.
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Old 08-18-2012, 10:26 PM   #11
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I was thinkin about building some ram air induction to lead air right to the intake and blocking off 75% off it
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Old 08-22-2012, 05:16 PM   #12
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Quote:
Originally Posted by djc1827 View Post
I was thinkin about building some ram air induction to lead air right to the intake and blocking off 75% off it
I recommend two things when people want to run a SRI. Try reusing the factory snorkel thing that's up top and front when you open the hood. Just hack up the section that would lead into the resonator box in the fender so it pulls air from the front and opens up right before you air filter. Or run a duct from the fog light opening or somewhere else with plenty of cool air up through your fender to your air filter. Neither of those will do any good if you filter is exposed to underhood air though.

Either way, incoming air will be heated up A LOT by your turbo then go through your FMIC so its a moot point. Fastest turbo cars I've seen draw open air from under the hood, usually just above headers. You aren't looking at any gains but if you really want to work hard for 1.5hp... have at it.
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Old 08-22-2012, 07:51 PM   #13
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My intercooler pipes and header are being coated as we speak, I didnt coat the fmic tho
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Old 09-26-2012, 12:42 AM   #14
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I would think that you could get the hood to vent if the bezel was thick enough at the front to cause some pressure creating a lower pressure area immediately behind it. That's why the wrc vent has a slight protrusion upwards. This is all speculation though. I don't know how high the bezel would have to be to create pressure at speed.
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Old 09-27-2012, 04:51 PM   #15
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my intercooler gets pretty beat up but i like the look without the guard
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Old 10-11-2012, 08:11 PM   #16
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i think you would have to be going extremely fast for that to happen for it to lift
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Old 10-12-2012, 01:48 PM   #17
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i think you would have to be going extremely fast for that to happen for it to lift
where did that come from??
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Old 10-12-2012, 04:04 PM   #18
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he is commenting on the first post of the thread...he is saying what everyone else pretty much said, that in order for the front to lift from doing this, you would have to go extremely fast.
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Old 08-27-2013, 03:37 PM   #19
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Quote:
Originally Posted by amalgrover View Post
some research was done by autospeed a while back on forward facing hood scoops and they actually found that at high speeds, airflow will reverse and flow out of the hoodscoop instead of into it.

basically i am saying that i highly doubt that the airflow into the engine bay will cause enough pressure to actually cause the front end to lift because there really isn't that much air hitting the firewall anyways.

even if there was a significant amount of airflow in there, the low pressure underneath and over the vehicle would cause the higher pressure air in the engine bay to flow down the backside of the engine, around the bellhousing, and out the bottom of the engine bay or out the hood scoop anyways.

in a nutshell, my opinion is that the decrease in downforce is going to be very trivial...at least at the speeds you will be going on the road or drag strip.

In the Autospeed article, they pointed out that the flow through the intercooler is much more dependent upon the pressure differential between the top and the bottom of the core (in TMIC); even more important that the air flow, per se. They used a Magnahelic gauge and demonstrated the necessity of a pressure differential across the IC.
Based upon this, I would imagine that anything that anything that caused an increase in under-bonnet (hence over IC) pressure would actually force more air through the fins. The one caveat being, there has to be enough exit vents to keep the circulation going...
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Old 08-29-2013, 02:51 PM   #20
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What are the hood scoop block/delete options for guys running a fmic 2008+???
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Old 08-29-2013, 03:04 PM   #21
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I duct tapped mine up...

Along with all the open spaces in the front.
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