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Anyone done hood vents?

55K views 89 replies 1 participant last post by  Brad96 
#1 · (Edited)
As I've gotten more and more into open tracking over the past 10 years, I've learned a bit more about aerodynamics. Heat extractor vents in the hood have all sorts of benefits - reduce pressure under the hood (thereby reducing front end lift), improve airflow through the radiator, let some air out over the car rather than passing under the turbulent, non-aerodynamic underside, etc. The hood of the V looks like it wants to jump right off the car when you're blitzing down the straightaways at high speeds, so I'm sure some vents would be effective.

So, I've been planning to vent the hood of my Subaru for a while. I've done most of my track days in the Subie and I think it would benefit from some hood vents, particular for the improved flow through the radiator. I've accumulated a variety of OEM vents off Ebay and from junkyards as I looked around for a possible solution. In the end it looks like the Subie's going to get a '10 Mustang GT500 hood vent, but that leaves me with some other vents to play with.

In all the pics below the trailing edge of the painter's tape is about where the trailing edge of the fan shrouds is. No point in having the vents any farther forward than that.

Here are some vents taken from a 80s/90s Trans Am GTA. As you can see in the linked picture, the larger ones were actually run 180deg opposite of what I'm looking for, so I guess they must've fed the air intake rather than acting as vents. Whatevah!




Another option would be to put them so they're venting out to the sides. The shape of them doesn't really work out too well - they wouldn't line up with anything quite right.




And then there are the smaller, side-facing vents. I think these would be a nice, subtle touch mounted in basically the same place they were mounted on the GTA hood. Line them up with the character lines on the hood and I think they'd look almost OEM. The down side, of course, is that they're not very big.






An older picture with vents from a 80s turbo Lebaron:


And the biggest, baddest vents of them all, the Lumina Z34 vents.




On the Z34's hood they were mounted to vent to the side, kinda like the second set of pics I posted of the Trans Am vents. I could also do that on the V's hood, and it doesn't look bad, but for whatever reason I didn't take any pictures in that orientation.

Although I don't have them with this set, as installed on the Z34 they had rain drip trays beneath them. I would have to either get the drip trays, or make my own, otherwise the engine bay would get doused in the rain. But I could just pull the drip trays off for the track.

They line up almost perfectly - if I position the side of the vents parallel to the character line in the hood, the front edge of the vents lines up pretty well with the front of the hood. It's not perfect, but since they're set back almost 2ft I don't think it would matter.


In the more expensive, blingier realm, there's these CF vents from Anvil Auto. I don't have a pair of those handy, so I can't show you how they would look on the V's hood. :) Here's a nice shot of them on a classic Camaro:


They're about 8x12". In comparison, the Z34 louvers are about 7x20".
 
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#2 ·
I would like the first ones better if you switched sides, then rotated them 180 degrees, so they follow the lines of the hood better.

The small 2-vent ones look good up on the top sides of the hood as well.

The big ones on the bottom look good, but i think they would look best higher on the hood
 
#4 ·
I would like the first ones better if you switched sides, then rotated them 180 degrees, so they follow the lines of the hood better.
I agree that they would follow the lines of the hood better that way, but the louvers would be facing the wrong way if you flip them 180. (They would want to scoop in air instead of venting air out.)

The big ones on the bottom look good, but i think they would look best higher on the hood
Interesting - I would actually say the opposite. :) I'd like to see them moved forward a bit more. I wouldn't want to move them back much, as you then start to get into the area of the hood where air stacking up in front of the windshield creates a high(er) pressure area that would reduce the effectiveness of the vents.

Although that's a Volvo S80 rather than a CTS-V, it's pretty representative of what a typical production sedan airflow is going to look like.
 
#3 ·
The Z34s line up better than the units in the first photo. I know the OP is aware of this, but they would be most beneficial if they were placed just aft of the radiator, not further back. The drip trays are a very good idea. I would love to see a continuation of your efforts, esp final photos.

You can't rotate the ones in the first photo, the vents would face the wrong direction.
 
#7 ·
Yeah i was just commenting on looks... functionality... that is another story.

just remember that GM put a lot of engineering into shaping things the way that they did. (not to say we can't make it better) There may be some benefits to not having a big hole in the hood for higher speed aerodynamics
 
#5 ·
Oh, and I'm not sure I'll ever really have the balls to do this. I guess if I can find a cheap-ass donor hood to cut as a test before I cut into the "real" hood? I still haven't had the guts to chop the Subaru's hood yet, and that car is a beater compared to the V. :lol:
 
#62 · (Edited)
Oh, and I'm not sure I'll ever really have the balls to do this. I guess if I can find a cheap-ass donor hood to cut as a test before I cut into the "real" hood?
Fast forward a few years and I finally sourced a cheap-ass donor hood. Checked the local Pick-n-Pull's inventory this morning and saw they had a 2006 CTS - the first time I've seen them have a CTS. I wanted to look at a couple things for my other 2 cars, so I headed over. The CTS's hood was not only intact and in decent shape, but someone had already removed it, so all the hard work was done! $55 out the door! (I occasionally look for them on Ebay, and even considered buying one a month or so ago, but about the lowest I've seen them priced was ~$250. Usually they're $300+ and then another $100+ freight on top of that, with the risk that the aluminum hood is going to get damaged along the way.)

It's not the right color, and the paint is pretty beat up along the center ridge (dragged on the gravel in the junkyard?), but for $55 I'm pretty happy. This project is still not real high on my list of automotive things to do, but having a hood to play with is definitely a step in the right direction.

Edit: Stock hood weighs ~24# (24.2# using the "me+hood" - "me alone" on my digital bathroom scale). That's complete - washer nozzles, "chrome" trim, hood liner, but no hinges.
 
#6 ·
Find out what a local shop would charge to integrate it into the hood and paint. There's a shop in my area that has done excellent work for me at a good price, so when I saw this thread, I thought "I'll bet they can do this and it may not cost an arm and leg".

I've had heat extractor hoods on Mustangs and Miatas, and the performance improvement was always outstanding. Problem with them was that water would get into the engine bay and corrode things. I ran the Miata on the street with open cell foam jammed in the vents if I suspected rain. Specter's hood has drip trays. Unfortunately, it's rather expensive. If I needed to upgrade the cooling system, I'd probably put my money on their hood first. Everything under the hood runs cooler, in addition to the aero benefits you've mentioned.
 
#8 ·
I'm sure their engineers worked their tails off, then the bean counters pulled the carpet from under them.

A properly executed heat extractor hood would have added cost and complexity to manufacturing the car, which would have been passed to the consumer in the price, and most drivers probably wouldn't have known the difference, so GM decided not to bother. A comparison would be that OEMs use idiot gauges for oil pressure and coolant temp rather than an actual functional gauge. Regular folk not interested in cars like it smooth and easy.
 
#9 ·
Don't use the TA vents. People use those on Fieros all the time and they're ugly. ;)
 
#11 ·
I really like the last pic of your car with the Z34 vents, that could look really nice if done properly. When I get my light issue figured out, I will post some pix of my SW Heat Extractor.

As for the added aero benefits: I am really hoping for a bit more of a planted feeling from the front end on high speed road courses, or while doing a top speed interstate run.
 
#12 ·
best appearance thread in months... i like the look of the z34 vents, looking forward to seeing pics of the next step in the process..
 
#14 · (Edited)
Mostly sourced from ebay over the years. And I forgot another set I've got, from the '87/88 Tbird Turbo Coupe. As you can see, on the Tbird they were inlets (not sure if they actually went to anything or were just for looks), but you could easily turn them around to use as vents. The opening is about 1" deep by 5 or 6" across. No pics of those mocked up on the V, as I don't think they'd be big enough for what I want.
 
#15 ·
I do not believe placement matters as much as the size. Given fluid dynamics.....would these not simply work like venturis? The rushing air across the top will cause a low pressure and draw air up through the vents while in motion?
 
#16 ·
You can't have it both ways. As you said, size is important - you want the things to be big enough to move enough air that they actually make a difference. But, the bigger they are, the less that venturi effect is going to work - you have some pressure difference between the relatively stagnant air underhood and the fast moving airstream on top of the hood, and the larger the area of the vent is, the smaller the differential pressure. You'll see on a lot of race cars that there's some sort of wicker on the leading edge of the hood vents to help generate a greater D/P.

And, just to clarify, placement does matter as far as where the radiator is. Going back to the Volvo S80 diagram I posted before, you can see that the light blue (lowest pressure on top of the hood) is towards the front. To maximize the D/P and make the vent more effective, I would want to put it in that light blue zone. But if I do that the vent is probably in front of or maybe right on top of the radiator, which means it's not doing much to help air flow. That's the mistake I made on my Mustang's hood - the hood vents I had added are too far forward, so I don't think they're as effective as they could've been a couple inches farther back.
 
#20 ·
So, any updates w/ the z34s?
I'm not sure when I'll actually get around to trying this. It's honestly not near the top of my list of vehicular projects, but I might get to it at some point this fall/winter.

Off topic question: any track days coming up w/in a 5 hour drive? I'm jones'n for a track day and since Luke had to cancel for November I can't wait until 2011. Also, how to you transport your track wheels/tires in the V?
I'm running Summit Point Main with the NCC BMWCCA on 10/16-17. Not sure if they still have any openings left (and no, I'm not a BMWCCA member). After that will be VIR Full in mid-November with the PCC Audi Owners Club - still need to actually register for that one (yes, I am an Audi Owners Club member, but Audi ownership is not required to become one). That may turn into a 3 or 4 day event, as Trackdaze is running the Mon/Tue after Audi's weekend event. Hmmmm...
 
#21 ·
Pat has it right with the Z34 vents. I picked up a complete set. Only problem is the drip pans are a no go. If you squint you can see them in my not so good dark garage picture. You'd need to be a bit creative to modify them.




The side mount vents just are not sexy enough.




Here's the best spot and I'm sure Pat agrees. My body guy can mount and paint for $500.00. A good value for an extractor hood that should really work.

 
#22 ·
Double post. Ooops.
 
#23 ·
I still have my set of vents, just haven't had a chance to do anything with them. I'd like to be able to find a used hood to butcher. And I'd need to find someone I trust to do the work, as this isn't something I'd want to give to any old body shop.
 
#24 ·
AAIIIC said:
I still have my set of vents, just haven't had a chance to do anything with them. I'd like to be able to find a used hood to butcher. And I'd need to find someone I trust to do the work, as this isn't something I'd want to give to any old body shop.
I got lucky and found a guy that's done quite a few. This is a popular mod with the off road guys and he's been doing Land Rovers and Jeeps. He's even done one on an STS.
 
#28 ·
Bringing it to the shop tomorrow for the Z34 extractor vents. I'll report back in about a week.
 
#30 ·
Its been done quite a few times in the Sy/Ty community with success. I think it would work...
 
#31 ·
Love Sy/Ty.... Would have bought one if i didn't buy the V.

Also would love to see how the hood turns out. I wonder if there are extractors similar to the Spectre Works ones that could be fabbed in.
 
#33 ·
The real challenge may be trying to work with all the structural bracing in the hood. I spoke to my body guy today when I dropped off the car and he said that sometimes areas of the hood need to be reinforced since it's a double panel and the thickness is variable. If you peek under the felt hood mat you can see that the V's brace panel looks a bit different than the BMW in AAIIICs picture. My guy has done it before several times but he says sometimes it involves more than just cutting out the holes. I'll try to get as many pictures of the process. The results will be interesting. I'll probably do some hood pins as well since the hood waves like a piece of paper at speeds above 130. My last track outing is October 13-14th at Road America so I can see if any of these changes work.
 
#34 ·
If you go that route, use the aero latches instead of the pins
 
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