[AAIIIC]

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".

 

[AAIIIC]

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.

 

[AAIIIC]

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:

 

[AAIIIC]

There may be some benefits to not having a big hole in the hood for higher speed aerodynamics

Highly unlikely. I can't think of any way in which the car would not see the benefits I mentioned in my first post. Obviously every car has its own aerodynamic peculiarities, but the fact that the area under the hood is at higher pressure than the air above the hood, thus generating lift on the front end, is going to be true of every sedan. Now, if the V was very light in the rear at high speeds, such that it was prone to spinning at speed, then reducing front end lift (adding more front end grip) would be a bad thing. But I don't think the V is that unstable at high speeds.

There's a reason that the cars in every sedan-based racing series have vented hoods (assuming the rules allow it, of course).

 

[AAIIIC]

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.

 

[AAIIIC]

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?

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.

 

[AAIIIC]

Any updates on this? im looking forward to your results im sure i'm not the only one. I really like the z34 vents. I need some vents on the hood to dissipate some heat.

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...

 

[AAIIIC]

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.

 

[AAIIIC]

Cool! Obviously, lots of pics are appreciated (including work-in-progress pics, if possible).

 

[AAIIIC]

I wonder if there are extractors similar to the Spectre Works ones that could be fabbed in.

As I mentioned at the beginning of this thread, you can find all sorts of vents and louvers if you search around. A pretty random example that I saw recently over on corner-carvers.com - the intake louvers from a 1970s snowmobile were used on an LS-motored E36 (they flipped the louvers around so they would vent out the back rather than act as scoops).

One of my saved searches on ebay is for louvers and vents (I haven't bought anything in years, it's just one of those things I look at). There are hundreds and hundreds of things that pop up. A lot of them are garbage that I haven't figured out to filter out of the search results, but there are all sorts of things that one could be creative with.

 

[AAIIIC]

IMHO, a much better use of time and money would be a ram air hood that would allow you to feed air to the intake through a straight pipe, doing away with that horrible 90 degree bend we have.

I'd rather have the aero, handling, and cooling benefits of a vented hood than the few extra HP one would get from a ram air setup.

i was thinking more along the lines of this:

:vomit: To each his own, of course, but I've seen a couple of those Challengers in person and I think the scoop looks ridiculous. On a classic muscle car the same thing looks awesome (the 60s Mopars, for instance), but on a modern car it just looks completely out of place to me.

Even a lower profile version (think WS6 TransAm or the GTOs) would look goofy IMO.

 

[AAIIIC]

Not even a sneak peek shot? C'mon!!!

 

[AAIIIC]

Looks pretty damn good, and once the shop figures out getting them level they should look great! Whoever came up with the idea is a frickin' genius.

I will say that I think my mock-up fitment looked better with the vents moved in a couple/few inches from the character lines on the hood. Does the underhood structure not allow for that placement, or did you just think it would look better with the outer edge of the vents lined up along the hood crease?

 

[AAIIIC]

This is what it would look like cut /modified/ frenched in.

Photo is of my v hood as a mold

That looks pretty badass. Any provisions for rain trays of some sort for those of us who are still using the car on the street?

 

[AAIIIC]

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.

 

[AAIIIC]

Yeah, I was planning on the Lumina vents. At some point since this thread started I found a set of the rain trays; they would have to be modified to be used, but they at least give me something to work with.

I'm all ears on the CF - shoot me a PM.

 

[AAIIIC]

Link to the ad? Were they selling the hood, or the car, or the D3 windshield banner ? (If it's the windshield banner, I'm guessing that goes for $225 new from D3. )

Edit: Found it - http://www.ebay.com/itm/CADILLAC-CT...es&hash=item339592b26a&vxp=mtr#ht_3231wt_1105. $325 for a hydro-dipped factory part. I haven't been able to find a part number for the factory part to look up what it costs without the hydro dipping..

 

[AAIIIC]

Fast forward another few years... I will probably be drilling and cutting within the next week or so. Got things mocked up on the spare hood I picked up way back in 2014.

The tape stripe across the hood corresponds to the trailing face of the radiator fans. I laid a big sheet of thin (somewhat see-through) white craft paper that I picked up at an arts-n-crafts store on one side of the hood, then used a cardboard template of the Z34 vent to mark about where the opening would need to be cut into the hood. Marked the 4 corners on the hood on that side. I then made some alignment marks on the sheet of paper and the painter's tape, then flipped the paper over to the other side of the hood to allow me transfer the 4 corners. Using the reference marks on the painter's tape, plus some reference points on the hood itself (the corners of the holes for the washer nozzles made for convenient measuring points), I made sure both sides of the hood were the same. They're not perfect, of course - I'm just eye-balling all this with a tape measure and a Sharpie - but close enough for government work.

These initial openings are actually going to be smaller than the Z34 vents would need. My intention is to try to test the difference at the track. By making a smaller opening, I've got ~1/2" around the edge so I can drill some holes and bolt things in place. My plan will be to have flat plates (to block off the openings = stock hood), tripper fences (just a fence along the leading edge of the openings), and rough louvers (some aluminum sheet that I'll slice and bend to make ugly louvers to approximate the Z34 louvers). Should be fun to play with.

 

[AAIIIC]

If you look back to post #21, the Z34 louvers do have rain trays. However, as shown in that pic, when you flip the louvers to mount them the way I want to, the trays aren't oriented correctly. I'll have to figure something out for that.

 

[AAIIIC]

Put my new HF 4-1/2" angle grinder to use for the first time Friday after work, go the driver side opening roughly cut out.

Now that I've got the first opening cut, I have a better idea of what's going inside the hood. I knew there was an inner and outer skin, but I wasn't sure how they were joined together to provide support. The inner skin has kind of a giant golfball pattern to it (as seen here), with each of the dimples being about 6 or 8" in diameter. It appears that the peak of each dimple has that foam adhesive to bond it to the outer skin. Cutting the opening leaves big gaps:

My initial thinking is that I can cut a series of slots perpendicular to the edge of the opening, and then bend the inner skin up to meet the outer skin. Probably seal over where they come together with foil tape to make it "air tight" and prevent air from getting crammed into that gap at the trailing edge of the opening.