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Old 06-09-2007, 06:13 PM   #1
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Default extraction hood

Inspired by http://www.rx7club.com/showpost.php?...78&postcount=9

Here are my plans. Areas outlined in black are the areas I plan to remove. Then I have to figure out the mesh. Will be used in conjunction with TSI's. Right now I have no front turn signals at all, I figure that's going to be a problem (ticket) eventually.

Comments welcome.
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Old 06-09-2007, 06:40 PM   #2
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Default what do you think about this?

I think a vent directly over the turbo will do the best job of releasing heat in traffic.
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Old 06-09-2007, 06:43 PM   #3
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Ben, the vent you have drawn on the passenger side of the hood looks to be right over the fusebox. I'm not sure i would do that for rain issues.
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Old 06-09-2007, 07:06 PM   #4
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For turn signals, wire your front parking lights to flash. Should be two butt-splices per side and some heat-shrink if you're feeling daring. I've been running with no blinkers aside from those for several months now with no issues.
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Old 06-09-2007, 07:21 PM   #5
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nice car ben why is it the real fast ones start off as silver yeah don't put a vent over the fuse box man that could be bad. Are you sure there will be enough area to flow the cfm you need to cool the setup?
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Old 06-09-2007, 08:24 PM   #6
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Good call on the fusebox. I should have thought of that. Glad I posted, I would have taken a hole saw to those areas to punch out vents for proof of concept.

One of the motivations for removing an area "inside the frame" is to assist me make the cuts. I am good at many things. Body work is not one of them. I think your concept is superior Rob. But I don't think my abilities are strong enough to make it come out looking right.

Richard, how affective they'll be, IDK. It's worth a shot. A hood was donated to me for the cause.
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Old 06-09-2007, 10:09 PM   #7
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Looks like a good project. Let me caution you on the TSIs (no turn signals in your case) as I have said it before, but someone actually took the time to pressure test TSIs and while they make your engine bay feel cooler, it is self defeating if you are doing the hood for heat issues b/c it actually pressurizes the engine bay (obviously less so with an extraction hood) which results in less flow thru the radiator (and IC for that matter) which kinda defeats the purpose of an extraction hood in terms of cooling/overheating. You might be trading radiator flow for engine bay flow which might not be the best thing. While your engine bay may feel cooler from the airflow, it certainly may worsen coolant temps. An extraction hood works the exact opposite by decreasing engine bay pressure thus creating more flow thru the radiator and more heat exhaust from the engine bay. YMMV.

As a solution that would make more sense if you are concerned about IATs would be something more along the lines of BEGI's cold air box with a NACA duct as you would get cool air to the intake without pressurizing the engine bay.
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Old 06-09-2007, 10:54 PM   #8
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Well Tom we will see. I have an AIT sensor and the ability to datalog it. Proof will be in the pudding. Or not.

Here's what I've learned so far early in the hot season. With default MSPNP fan control I would run between 205-211 F on the street. After boosted runs it takes a long time to cool down from 211 to 205-206. With the turn signals removed I run 203-207 and occasionally hit 211 briefly on boosted runs. The cool down from 211 to 203-205 takes a minute or so. With turn signals removed and the second fan coming on at 206 I run 203-207. Haven't seen 211 yet. My Peak IATs (130-133F) are the same after mods, but IATs return to "normal" (100-110) much more quickly with the turn signals removed.

Tells me a couple things.
  • Getting air flow across the motor is a good thing
  • The under hood area is definately pressurized because the cooling fan shouldn't make a difference when driving at speed, BUT IT DOES.
  • My CLT and IAT are lower with the turn signals removed. Datalogs show it
As far as a cold air source for the intake. That will be addressed. But what I've noticed after getting home is that my intercooler feels cool to the touch, as does the cold side pipe going towards the throttle body. However the throttle body up pipe is HOT to the touch, like the intake manifold. Getting airflow across the intake mani should help keep IAT down.

Now my plan is to place vents in two locations. First, a vent behind the radiator to hopefully facilitate drawing air through the mouth, various mouth located heat exchangers, then out the hood's first vent. The second vent location is to facilitate drawing outside air across the engine compartment while driving. I'm hoping that the cumulative effect of all the vents will more than offset the additional pressurizing caused by TSIs. If warranted, additional vents can be created, or the originals enlarged if possible.

I have datalogging capability and use it every time I drive alone. If the plan works or fails, I will have little invested in it. I can ride with and without turnsignals to see if there is a difference after the hood is opened.

I'm picking up the donor hood tomorrow morning. I plan on running the front vent, no matter where the rear vents end up. So I'll go ahead and take a hole saw to that area in the front and see what happens.

IMO, it's worth a shot. The worst thing that happens is I destroy a hood that was going to be thrown out anyway.

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Old 06-09-2007, 10:57 PM   #9
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nice i look forward to this if it works i might massage mine some more and get a cold ram air intake.
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Old 06-09-2007, 11:59 PM   #11
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I really like how this venting was done. I'll be doing similar on mine.

http://www.clubroadster.net/forum/viewtopic.php?t=9191
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Old 06-10-2007, 12:32 AM   #12
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Or.... my photoshopped variant....
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Old 06-10-2007, 12:54 AM   #13
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OK, how's this? 3 small squarish vents up front, 2 wider rectangular vents near the back of the hood. Thinking I'll try to 2 blue ones first, and if needed, go for the 3 red ones too. One of my thoughts was with a basic rectangular shape, I can use some body filler to make small lips on the leading edges.

I have to keep it simple. I'm not good with body work or metal fab.
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Old 06-10-2007, 01:00 AM   #14
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Why not just do one strip up front? instead of 3 little rectangles? Like the first picture I posted, but more towards the front and wider.

From the hunting around for ideal venting and such... I'll be doing the 3 ducts (could be one, I guess its the ricer in me wanting to do 3 in the space of one) in the hood as pictured and an undertray. Enough to develop airflow for the radiator/fmic etc.... and thats the focus.
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Old 06-10-2007, 01:07 AM   #15
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Like this? Possible. Just afraid of cutting the "frame rails" close to the hood support. What I do like about this is again I could build up a lip on the leading edge, that would not only create a greater pressure differential, but could look pretty pimp too.

Dave, bear in mind your fab skills are far more advanced than mine. Not that I'm bad with my hands, just no experience with this (and no proper tools)...
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Old 06-10-2007, 10:10 AM   #16
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From my hood modification browsing, I've seen a few people cut out all the webbing on the hood except for the frame around the edges. They've said it makes it flimsy while open, but no issues while closed. I had planned on no skeleton for mine... and also was thinking of the leading edge having a lip.

It should just require something like a dremel and a set of pliers and patience.
Plan was to tape it off, mark it up, cut a very wide H, with the lower side of the H being much smaller than the top. Then carefully starting to tweak the metal on both sides until its where I want. I'll be adding sides to mine, but I have a friend who can TIG... so thats kinda helpful
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Old 06-10-2007, 11:57 AM   #17
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So you're saying just cut the "H" and bend the hood at the slit to form a shape. Not just cut a big rectangle. Sounds like a plan.

I don't have a 'real' dremel. Mine is the rechargable battery kind, 12V IIRC. Not up to the task. My buddy has a JIG saw. Was going to use it with a fine metal blade, as recommended earlier.

Should I heat the metal up when I bend it? Or use something behind it to "curl" it in the shape of a vent. Hmmm...
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Old 06-10-2007, 12:16 PM   #18
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re: tsi - rather than contending with the tsi pressure issues, put a 3" hole under the driver headlight and build a box around the headlight and airfilter. The turbo doesn't need any pressure, just a cold air source. This way you'll get what you want/need - cold air source w/o the pressure.

I think a cutting wheel is the tool for the job- saw blades/teeth are a bit too rough for the thin aluminum. I did a bunch of cutting on a hood for engine fitment and it was all with a 4" grinder (wheel gaurd removed) and metal cutting wheel.

good article on shroud engineering for the mouth
Just like a turbo setup, you can improve the system without having to go "bigger" - scroll down to "the curves have it"

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Old 06-10-2007, 12:28 PM   #19
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On a different car with an aluminum hood, I had success using those small cutting wheels made for a handheld drill.
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Old 06-10-2007, 07:07 PM   #20
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I went to HomeDepot and picked up 36 TPI very smooth cut, thin metal jigsaw blades. I also got some 3" metal cut-off blades and a mandrell to use them with my cordless drill. I can give it a shot, and hopefully clean up the edge easily with a grinding point on the drill.

I'm going to try Splitime's "H" concept and bend the leading edge up a bit, and the trailing edge down a bit. If I screw it up, I'll just cut a big rectangle out.
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