[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".

 

[Dan_Gurney]

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

 

[soflarick]

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.

 

[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:

 

[soflarick]

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.

 

[Dan_Gurney]

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.

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

 

[soflarick]

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.

 

[UnsafeAtAnySpd]

Don't use the TA vents. People use those on Fieros all the time and they're ugly.

 

[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).

 

[tweeter81]

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.

 

[shadybx7]

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..

 

[kirchbed]

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

Exactly...

AAIIIC - think the z34 vents are right for the build. I would definitely fab up on a junker hood before you proceed with your car though. Looking forward to updates. Curious how you sourced so many different hood vents. Locally?

 

[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.

 

[bneal1022]

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?

 

[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.

 

[MIAdragon]

Im already looking for a hood to try this out on, hope to find one this week!

 

[MO POWA!]

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.

 

[kirchbed]

You can't have it both ways. As you said, size is important...

So, any updates w/ the z34s?

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?

 

[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...