AVO Large hood scoop - with pics

[rc0032]

Paul – Can you give us a little info on what it takes to install this bad boy? What holds it in place? Can we get a group buy?

Thanks!

[apexjapan]

Without having one right in front of me, I have to go on what I do know. It looks to bolt into place via stock bolt-on points. I need to go look at my car to verify. A group buy is certainly possible, though I'd like to keep to my general conditions - 5 or more, and we'll just send them out individually because it tends to be the same cost/cheaper overall to do it that way.

 

Cheers,

 

Paul Hansen

[relhok]

Call me crazy....I like the way it looks. I don't like the fact that it sticks over the stock one.....seems like a silly add-on like a fake cell-phone antenna or fake side gills you see on Civics.

 

Those vents on Civics evacuate air pressure from behind the fender and keep the flimsy plastic fender liners from blowing out at high speed. Of course, you would have to drop a Civic from a plane to achieve such speeds.

[OCDetails]

Unless it is going to do something that the stock scoop isn't accomplishing, then I don't see the reason for it. Especially if its just sitting on top of the factory scoop. Wouldn't it just ackt like a bucket and actually hinder performace rather than help it? I'm all for appearance mods, but if it is hurting performance rather than helping it, then I don't think I'd go for it. Besides, if the Legacy had any larger of a scoop than it does right now then I likely wouldn't have bought it. I like the muted look of what we have.

[ellivnad]

Attached is a pic comparing the stock vs scoop "overlay". I think it will certainly be functional. The cross-sectional area of the scoop exposed to the air blowing on the front of the car as you are driving is increased quite a bit. Even though the actual opening over the intercooler hasn't increased, the air pressure due to the scoops larger x-section will increase, and therefore the air flow (cfm) as well. As far as looks go, I didn't like the look on the black car, but it looks hot on the red wagon IMO. Its a nice halfway point between legacy and STi.

[OCDetails]

If it is just overlayed on top of the stock scoop, then how is that increasing anything? To the intercooler the opening hasn't changed a bit. Unless this is a replacement for the factory scoop, then its not going to do anything useful.

[ellivnad]

It's funneling more air to the intercooler. Think of it this way. Its raining outside. The rain represents the air that would be flowing over your hood. You put a glass on the ground, this represents your intercooler, the mouth of the glass represents the size of the stock scoop. Now add a funnel to the glass, the glass is sure to fill up faster, there is more flow into it.

[OCDetails]

I can see what you are saying, but I don't think this is like a funnel. Its more like a glass in the middle of a bucket. Picture a bunt cake pan. If you held that up to a wind tunnel, do you think the velocity in the center hole is going to be greater because there is that larger opening surrounding it? That is kind of what I picture this to be like.

 

http://www.ballarini.it/prodotti_img/15515GF06.gif

 

Cut that bunt pan in half and you have what this scoop is. Its a larger opening with no exit surrounding the same scoop you have now. How is the velocity of air going to be greater in the stock scoop just because there is an opening around it? I'm not trying to argue... I just don't understand the physics of this I guess. To me it is like parking in your garage while the wind is blowing into it. The scoop doesn't get any more air just because there is a larger opening surrounding the stock scoop.

 

Here is an illustration that sort of shows what I'm saying. The extra size on the scoop doesn't have anything to do with how much air is going to go into the smaller one. All its going to do is increase drag because the extra air that goes into the larger scoop would have nowhere to go. Of course... if this just replaces the stock scoop then I can see how it would be helpful. Or if this one had some sort of way of closing off the back of it so it actually was shaped more like a funnel then it would work well. I guess my confusion is in not understanding if the lips of the two scoops somehow have something connecting them that actually enlarges the opeing of the scoop. I guess I can see it would be good if that were the case.

[OCDetails]

Hmmmm.... This picture doesn't make it look like this scoop is just sitting on top of the factory one. I don't see the factory scoop under there. I don't see it in this one either.

[ellivnad]

I think the scoop is more like my horrible picture below. The black being the hood with scoop opening, the red being the new scoop. The new scoop would seal against the lip of the old scoop (thats why it looks like the old scoop is gone to you) and the bulk of the new scoop that sits back farther is purely asthetic. We need someone who knows fluid dynamics to jump in. I think I might be filling you with crud on some of my assumptions in previous posts, and while I still believe it should make a difference, I think it may be less significant than I originally thought.

[OCDetails]

That is what I'm thinking. The lip of the new scoop would somehow have to seal against the old scoop to be at all functional. If that is the case, then it just comes down to the appearance factor. I still don't like the look of the bigger scoop, but if it is functional then I won't laugh at the guys who put one on.

[ChE Outback XT]

Warning: Geeky argument ahead. Read at your own risk.

 

I've done quite a bit of research in fluid mechanics and, as a chemical engineer, took an entire course on heat exchanger design (an intercooler is an air-air heat exchanger) so I'll take a stab at this discussion..

 

1. The amount of fluid, air in this case, pushed through the intercooler is a function of the pressure difference between the front and back of the intercooler.

 

2. The area of the intercooler inlet doesn't change, so we are really talking about increasing the force placed on the air at the inlet. (The inlet is represented as the dotted line on my diagram.)

 

3. The force at the inlet is directly proportational to the force applied at the scoop opening.

 

4. The force applied at the scoop opening is based on slowing the air from its original velocity (force = mass x acceleration). The more air you slow down (more mass), the greater the force. Scoop B will slow down more air, and will thus apply a greater force and greater flow to the intercooler.

 

Notes:

 

- There is back pressure at the scoop from the intercooler and the engine behind it. (It's easier for the air to flow freely around or over the scoop than through the maze of the intercooler and everything behind it.) This means that not all the air heading towards the scoop will go through it (indicated as red flow-lines).

 

- Fluid mechanics assumes a no-slip boundary condition at the surface of the hood. This means the air molecules directly adjacent to the surface of the hood are not moving... hard to believe, I know, but it works in the math. This stagnant air pulls on the air above it and that air pulls on the air above it and on and on... This leads to a velocity profile where air is moving faster and faster as you move up away from the hood until you reach the edge of the boundary layer where air is flowing at the same speed as the bulk-air not affected by your car. This amplifies the effect of a large scoop as it gets taller, but not wider.

 

 

- OCD's example correlates to situation 2 in my diagram, where no air would enter the intercooler through scoop B that wouldn't have with scoop A. I contend that scenario 1 is actually what would happen. Of course increasing the size of the intercooler would allow even more air to flow, but the size of the scoop opening contributes, as well.

 

- Finally, it must be said that this is an almost purely academic argument. The amount of cooling air fed to the intercooler simply controls how warm the cooling air will be when it leaves the intercooler. (Cooler exit temperature means a higher temperature difference in the intercooler and more energy (heat) removed from the air heading for the engine.) Once there is enough cooling air flowing to keep its temperature constant through the intercooler, pushing more throught won't help at all. At that point, the only way to increase the effectiveness is to make it bigger (increase A in the q=UAT equation), make the intercooler transfer heat more efficiently (increase U, the overall heat-transfer coefficient, in the equation) or decrease the temperature of the cooling air (increase delta-T, only possible by making it colder outside). I would argue that our stock scoop already feeds enough air to reach this threshold and increasing its size is an aesthetic difference.

 

 

I hope this helps a little bit. Let me know if you have any questions on the geek stuff... believe it or not I love this crap.

[ellivnad]

Nice write up! Thanks for taking the time.

 

I would argue that our stock scoop already feeds enough air to reach this threshold and increasing its size is an aesthetic difference.

 

I would tend to agree with that. I believe that subaru probably did a bit of engineering to maximize the profile of the stock scoop and matched it with the efficiency/size/shape of the stock intercooler. This overlay is more likely to produce functional gains when you switch to an aftermarket intercooler like perrins. Then the additional cfm airflow will have energy to remove (assuming the aftermarket intercooler is more efficient thermally and not just more efficient flow wise internally).

[ChE Outback XT]

ellivnad - I agree with you that Subaru probably knew what they were doing, but I don't think any intercooler that fits under the GT/XT hood would benefit from a larger scoop (unless, of course, everything from intercooler to hood opening to scoop was wider). If we have enough cooling air flowing that it's not significantly as it passes through 4 or 5 inches of intercooler, an additional inch or two of thickness won't make much, if any, difference.

 

One more note from my geek-analysis above: The overall heat transfer coefficient, U, is proportional to the square root of the velocity of air flowing through the intercooler. Velocity is a function of flow volume which, as argued above, is a function of hood scoop size (regardless of hood opening or intercooler size). This means that, in order to double the heat transfered, q, you would need 4-times as much air. That would be one big honkin' hood scoop. (And doubling q won't even come close to doubling the effectiveness of the intercooling as the delta-T term will shrink as q grows.)

[slip304]

it better do a whole lot for $560.oo! You can buy whole c/f hoods for less than that. Not for a legacy of course but you get my point. I dont care how much air it flows for that silly price. I probably sound cheap to some of you but honestly that alot of money for a scoop that we cant even agree improves anything. Just my opinion.

[apexjapan2]

Unless that scoop has been butchered from the original test pieces that I saw ages ago, then it is a full replacement scoop, not just an overlay. By virtue of the larger intake area, it should increase flow through the IC when the car is moving.

 

They do a version for the BE/BH too, based on the S401 intake. Subaru claimed that the larger intake increased flow through the IC by about a factor of 2 IIRC. Of course SoJ won't sell you an S401 intake, so the new one being discussed is the only option BE/BH owners - but I digress.

 

In short, for the BL/BP owner, the intake being discussed should provide more air flow to the IC too. The S401 look alikes were well made, and I would think the new ones are of similar quality.

 

HTH

[PGT]

Why the exorbitant price for a non-Subaru part? I could almost understand the U$350 cost of the JDM sport grille given OEM quality, but almost $500 for a hood scoop from a third party?

[03Indigo]

I agree, WAY expensive for a small part. I have friends who make carbon fiber stuff, and even plastic molded stuff is not that expensive, for such a relatively small part that sticks on with tape.

 

for example, here is an entire carbon fiber hood for a MINI Cooper S, $849. Not bad considering the engineering that went into it, and the size of it..

 

http://www.m7tuning.com/products/cfmcsbonnet2.htm

 

http://www.m7tuning.com/cf_hood_400forpp.jpg

[DeepFreeze2]

It's not bad, but IMO just the scoop alone would throw the looks of the car off. If I were to do it, I'd do a body kit as well.

[IwannaSportSedan]

Have you guys looked around at http://www.k2k2.jp?

 

I have to admit, I really don't like the add-on scoop.

 

However, some of their other stuff it quite nice, but probably still expensive. I do strangely really like their M5 ripoff bodykit for the new Legacy. I usually don't like such blatant plagiarism.

 

Personally, I hope they, or better yet, someone who deals in the US would come up with a version of this rear window lip spoiler for the new Legacy sedan. This would look kickin' with an STi or other good trunk lip spoiler.

 

http://www.k2k2.jp/img/ef506.jpg

http://www.k2k2.jp/img/ef504.jpg

 

I do wonder if this peice hurts or helps laminar airflow over the rear window. There is a certain angle, like 27 degrees or something, where airflow becomes unstable going up over the roof and back over the rear glass. Shallower than that certain angle, and it is fine, but steeper, and the airflow just separates from the surface cleanly, with low pressure underneath it. (like off the back of a pickup cab) But at that transition angle, the airflow gets turbulent, and a spoiler like that one can actually help maintain airflow.

 

There seems to be some other tasty bits on their website, too. I don't like headlight eyelines in general, but they have a wagon taillight eyeline kit that lowers the tail light upper edge to the body crease line, which actually looks quite good.

 

HEHE, they even have a kit that changes JDM BL Sedan tail lights to have the tail markers on the bottom, with brake lights only at the top, basically turning JDM taillights into USDM tail lights with amber signals in the chrome center section, with the reverse lights.

[wayne53]

I wonder what spoiler is on there in that pic? I don't think it would look goot with the stock spoiler, though.

[fbi012]

this looks like the old legacy to me, is it?

[IwannaSportSedan]

yep it is a BE(? previous generation) JDM Blitzen sedan.

 

I think it would look great if a current generation version of that roof spoiler were made, and paired up with the STi rear trunk lip spoiler. I don't think it would go so well with the USDM wing spoiler, but I am not the biggest fan of that one, anyway.

[CJC]

Definitely like it. The first one looks good, but doesn't look like it would grab much more air. Any more information available for this one? I'd jump on it if they're available in the States.

 

I agree--this body kit is really sharp. Anyone know where it comes from??

 

CJC

[panamajack]

I belive that spoiler is from the Blitzen edition. It was co-developed by Porsche