extraction hood - Page 6 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 07-27-2007, 11:53 AM   #101
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all you need is a vent that pulls air out, not pushes air in.
im wondering about that scoop too, it would work just like the 600 track dog racing hood, but cheaper. the only problem i see is that it would weaken the already thin, light, weak miata hood. but who needs a strong hood?

but, there are also a lot of aftermarket scoops/vents that dont work, there just for looks.
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Old 07-27-2007, 11:56 AM   #102
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the hole would weaken the hood but the extractor "scoop" would strengthen it post hole. Cheap- but nowhere near cheap like Ben's mod.
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Old 07-27-2007, 12:02 PM   #103
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i agree, but i would do some more searching and find out what makes those type of scoops effective. then look for a cheap scoop that has those features.
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Old 07-27-2007, 12:06 PM   #104
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You don't need "features". You need a hole. Air travels from high pressure to low pressure through said hole. Done.

Just use a common sense approach.
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Old 07-27-2007, 12:11 PM   #105
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im just saying, it would probably be most effective to get a scoop that lets air out while not moving and draws air out at speed, to do this, you'll need "features".

plain holes in your hood will let air in at speed, not good.
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Old 07-27-2007, 12:14 PM   #106
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Brad i think you need to sit down and rethink this abit, i highly doubt they are getting a flow reversion to the point of creating a high pressure zone behind the rad a reverse scoop would be alot more effective + no worries about rain if i do mine i will do a reverse scoop for sure.
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Old 07-27-2007, 12:19 PM   #107
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agree to disagree. im sorry, didn't mean to affend anyone who wants to do the "hole in the hood" thing, im just willing to pay for quality. you and everyone else on this forum are diy's, im not. the holes would work fine i guess, but the extraction vents would be best.
probably not worth the money for a street car though. i see your point.
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Old 07-27-2007, 12:28 PM   #108
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I think you're missing the point. Look what Ben did to his hood much earlier in the thread. He cut a hole in it and formed some of the trailing sheet metal to form something similar to an extractor shape. It worked and it was free.
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Old 07-27-2007, 12:28 PM   #109
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Quote:
Originally Posted by bradh88 View Post
im just saying, it would probably be most effective to get a scoop that lets air out while not moving and draws air out at speed, to do this, you'll need "features".

plain holes in your hood will let air in at speed, not good.
You're on the right path. But having the scoop over the hole is by far and large cosmetic.

Sure you could have a scooper on the bottom of the extractor, and a little raised lip at the leading edge on top to create a larger pressure delta. They may be slightly beneficial to extraction. But the point is, the air moves through the hole because it is equalizing pressure. IE moving from high pressure to low pressure. The top section of the hood is a low pressure zone. No vent, duct, or scoop can work to counter this. That is why hood mounted Ram Air induction vents are not effective.

Yes, on my hood I bent the leading edge up and trailing edge down. Honestly, if I got a second crack at it, I would just cut out the rectangular vent without bending the edges. I am not comfortable with the body work necessary to make them look right. And by not having the trailing ege come down, the actual vent area would be larger.

My hood was a low cost (almost no cost) experiment. If I had a bunch of extra money, I'd go with a aftermarket extraction hood like FM's or the one that RotorNut posted.

Oh, and I still have not cut a vent over the turbo. But it is my feeling that having a vent behind the radiator to encourage flow through the mouth coolers, coupled with TSI and/or NACA intakes flowing fresh air across the motor surfaces and through a second set of vents closer to the windshield is the ultimate solution. Think of it as a combination of FM's hood and Rotor's hood, but using stragegically located smaller vents.

Last edited by Ben; 07-27-2007 at 12:40 PM.
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Old 07-27-2007, 12:47 PM   #110
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yeah the scoop thing was what i was trying to say, before spending money on anything, i would look up why and how the bumps,slants, etc. work to get more air out. then id look for the cheapest way to try to copy that.
also wouldn't the engine bay be a low pressure zone? dont know but thats what iv heard, probably wrong.
finally, what u were saying about the holes, i was thinking along the lines of the hood raising and holes back by the windshield, which i know is a high pressure zone.
i personnally dont like the looks of the holes. but thats not what we were going for here.
sorry for the mixup, my bad (...im new here)
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Old 07-27-2007, 12:48 PM   #111
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ahh, and another experiment I want to try is removing the undertray, or at least the "rear" part of the undertray. Rob's experience w/o undertray was that his hood balloned out at speed. I think he mentioned at around 100mph on the track. Which tells me that there is a wonderful source of fresh air available under the car, but it has to be allowed to escape from the engine compartment if let it. Otherwise it defeats the entire purpose of the effort. But if sucessful, it could be a constant supply of air moving from the bottom of the motor to the top, and out of the hood.

Complete removal of the rear half of the tray may be a bit extreme. A possible solution may be to cut a couple of vents in the tray with a hole saw. If it works, I might be able to leave my turnsignals in the nose. Which I would prefer to do as I like my twilights a lot. Corky Bell says he recommends ditching the undertray completely. I'm not sold on that concept, but find it interesting that he is. Perhaps his cool air scooper and hand made intercoolers are just that damn good.

brad, here are some pics from a car with this same type of mod completed. I know it looks like *** unfinished, but check out this hotness

More pics:
http://www.rx7club.com/showpost.php?...78&postcount=9
That's with some cleaning of the edges, screen I dunno epoxied maybe, and paint.
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Old 07-27-2007, 12:57 PM   #112
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wouldn't you want air to come in through the nose and rad?

do you have any pics of your car, i want to see these twightlights.
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Old 07-27-2007, 01:05 PM   #113
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nevermind, just read your edit and it makes sense.
the rx-7 looks good though, too good, i would NEVER be able to get holes to look that good.
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Old 07-27-2007, 06:14 PM   #114
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I hear alot about corky bell's recommendations...don't forget that he uses an air scooper for the rad, which moves a ton of air to the front of the radiator.
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Old 07-28-2007, 10:06 AM   #115
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Default and so it begins:

the future turbo hood vent. Just got through whittling from a block of wood.
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Old 07-28-2007, 10:56 AM   #116
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Quote:
Originally Posted by m2cupcar View Post
the future turbo hood vent. Just got through whittling from a block of wood.
did you whittle out a T/A too

What does that look like on the underside?
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Old 07-28-2007, 04:22 PM   #117
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I'll start a thread with some pics when I get it... from the NC countryside. It's fiberglass with a metal screen it and not overly large. Should do what I want position right over the turbo.
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Old 07-28-2007, 04:46 PM   #118
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the stage 21 hood is a really nice extraction hood

http://clubroadster.net/forum/viewto...highlight=hood

He, cut all but one of the rear vents to allow more air flow.
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Old 07-28-2007, 09:44 PM   #119
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That looks like a good solution- unfortunately none of these after market hoods take my engine swap into consideration.
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Old 08-03-2007, 10:19 AM   #120
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Next course of action:
http://cgi.ebay.com/ebaymotors/1981-...QQcmdZViewItem

PS, any of you ******* bid on that, and I'll ban you.
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