cbrf4i1,

I purchased the precut and screened unit from Halltech, and hope to install it this weekend.

Does this do what you are referring to? Same two holes you mentioned, just a lot cheaper.

 

yes sir. the piece that you need to replace with the halltech unit doesn't have the 2 holes cut yet. so you are paying for the cutting of the holes and the screen plus and the ability to go back to stock appearance if you want to at a later date. i just got a screen at home depot 36" x 4" and grilled the entire area. (take a closer look of that link i provided) frankly, removing that piece is more pain then the schroud, so i am not sure too many people would be putting it back to stock if you want to save the stock piece.

 

Now that I see how easy it is to detach the bottom of the shroud--and don't have to worry about cutting the a/c condensor, I may do both. The hood seals the air filter chamber/compartment to some degree and will create a positive overpressure situation with air pushed into the compartment from below. Again, no ram air, but a huge improvement over the stagnant air in the chamber without the opening to outside from pushing or cutting the shroud. The engine is going to suck the air in, but the fact that there is overpressure and much cooler, denser air will give almost the effect of the Vararam, or at least it seems to me it will. Again, say 15 hp, which seems very likely, and for zero cost. Add in a better filter system, like the Halltech, K&N or SLP and the results are indisputable.

 

Are you sure there is a seal between the hood and the rad support?

It seems to me that the stock airfilters draw air that has traveled through the radiator, and flowed back over the radiator support to the nose compartment (the area above the shroud). There are no openings forward of the radiator support, in the nose compartment. The stock air filters also draw from the top, not the bottom which leads me to believe that they are catching the air coming back over the rad support. The placement of the air bridge over the radiator support also suggests that there in no seal between the hood and the rad support.

Without an effective seal, the only benefit you get is cooler air into the nose compartment. That is, by itself, a good thing, but I think it could be improved with the addition of an effective seal to creat the positive pressure you refer to.

 

I think that Vararam/Haltech cover/panel (or a variation on it) that Pipedreams over in the C6 general section sells could maybe help in sealing things off a bit possibly.

 

The way I thought out mine is that the outside air impacts the radiator shroud and creates a swirl away from the impact point. The cut I made is directly infront of where the air starts moving forward,away from the shroud, creating an ever increasing(as speeds increase) force of air for the K&N. While this will not show up on the dyno , it should help pull in cool air for the intake while at speeds.There is minimal areas for fresh cool air to enter as the car sits stock. I also "sealed" off the entrance to the engine compartment with foam weather stripping( to stop debris and other dirt) and the K&N still recieves the air from the other stock locations as well. The way it was made the intake feeds off of alot of the underhood warmed air. If I gain .05 at the track for this , i have $3.00 total in weather stripping, so thats a good gain. If I gain nothing, oh well, I burn $3.00 worth of gas sitting in traffic on the way to the track anyways....All in all, it appears to have a better flow of fresh air to the intake and still has no obstructions to the radiator.

 

there is a good 2 inch ish gap between the hood mate and the top of the radiator cover / support..by the air filter bridge area that gap is more like 3 inches. i made a foam that sanwich between the top off the radiator cover / support and the hood. so it does seal off the nose area from the engine compartment for the most part. area around the hood hinge is the only area hot engine compartment air could travel back to the nose section. problem is i can't seem to find any foam that is black, so this thing is an eye sore.

 

The shroud is between the condensor/radiator and the airbox/filter. With the bottom opened, it will only draw cold, outside air. The airflow will push any extra to the engine, not allow for engine heated air to come to the filters. That is the ingenious part of the free mod. I have an Aircharger, so no draw at all from the top, just the bottom with the venturied cold air coming up from under the car in what is a high pressure area.

 

Just finished the install. I used those chrome rods with the plastic ball on one end, down about an inch or so that you use for the popup on a drain. The ball fits into the shroud opening perfectly, and the other rod end goes into the backside of the front clip, one on each side. They hold the shroud open 3-4 inches, equally, on each side. The great part is that the pushed back edge of the shroud now is into the slipstream that comes in thru the front grill, as well as getting air from under the car--both directly almost perfectly up into the K&N Aircharger with its huge swept area. For some reason, when cold, the throttle is much more responsive than it was starting out in low gear--seems like a smoother, higher rev so it's easier to launch. And at highway speed in 3rd or 4th: what a difference!! You can really feel the car open up--especially here in high elevation. 4th, which is a 1:1 ratio, is like a passing gear at 45-70 in an automatic! I doubt the Vararam gives any substantially better hp increase than this mod--at least with a huge air cleaner like the Aircharger, Blackwing, etc completely open to the bottom of the chamber and the leading edge of the shroud acting as a director of colder air than the Vararam would get with the shroud cutout. For a free mod, I am blown away by what it gives in sotp and real power adders. Plus, the rods and ***** look fine, not like some taped on crap, and they aren't going anywhere nor will they be damaged by exposure. And the car is also running 4 degrees cooler, 192 vice 196 cruising at 60-70. The computer still has to learn the new denser charge, so I'll be interested in what it feels like in a 100 miles or so. Anyway, I highly recommend this to anyone not having a cutout type of airbox. It takes 5 minutes of your time and can be put back to stock in 15 seconds.

 

whiterock, can you post some pictures? i am curious how you are able to put it back 3-4 inches. thanks

 

Yes-please post pics. I'm trying to imagine what the chrome rods with the ball thing is.

 

I never even thought to use two things to prop the shroud back, I merely have one prop in the center (a thin/flat piece of black plastic leftover from opening up of the airboxes, strategically placed to cut the air as it enters the area ) but it only hold it open about 3 inches and that's only in the center.
I might try two pieces to get a more uniform and larger opening.

 

does this mod need to be done from the inside of the engine bay or the outside? I have a racemesh grill on my car and cannot get in there from the outside.

 

It is far better than just the one prop in the center. I'll try some pictures--not great as a photog , tomorrow when the sun is out. Not sure how to post them, though. Perhaps I can email them to someone who knows how. The rods I'm referring to come with a drain kit for a bathroom sink. They fit into the drain and are what levers the popup that closes the drain up or down. About six inches long, chromed, with a white plastic ball about an inch and a half down on the rod on one end. The were the perfect size and absolutely secure when used as I said.

 

I think Joe's analysis is spot on. I just added an air charger (which comes through the shroud), halltech race filter and tune to my z06 and it's a monster now. That made a big difference over stock, and the weather is the poorest it's been da wise in dfw in many months (80deg/70% hum). Underood looks identical to stock with the factory airbox back in place. very stealthy and big bang for buck

 

question , how are we sure that the opening does not actually cause a vacuum as the fast moving air rushes past that newly created opening?

 

Air comes in through the grill opening and is directed by the angle of the shroud upwards. The underbody air is a high pressure area back to the airdams then up to the condensor. The lower high pressure area aids the air thru the grill to funnel up to the filter. Air flows from high to low pressure gradients and the airdams work as a kind of stop for the flow, keeping high pressure below the new open shroud and aiding the grill air to flow upwards. Or at least that's what my Fluid Mechanics PhD tells me...nice to have brainpower working for you The only low pressure area in the process is up top of the filter which also helps the air to flow in that direction.

 

Whiterock1 - How did you get those bits in anyways? I had one of these from our new house build that looks right but there is no way i could pull the plastic back enough to get that guy in there. Maybe shorten the 1.5" end? pull harder ?

Just adding a block in the middle was interesting though, it seemed to affect the idle in a positve way (smoother). Way to early to tell anything else but no real SOTP difference with that small opening.

Any luck with the pictures?
GPK

 

I just layed in front of the car (on the ground) and reached under the grill. A small, thin open end wrench fit in to pop the push pins out. I had to fuss around a bit with one of the rods to fit it, but it took less than 10 minutes total, and I was feeling my way through it. You don't have to worry about going in thru the grill, but you can really see what it looks like thru it after. Sorry, no pictures. Camera went tango uniform, but the link to the first site does show what it looks like from the top. Once you have the pins out, you can by feel see the holes in the back of the front clip, and the ones in the shroud are visible thru the grill. Really is an easy mod.

 

Good question, I've wondered as well what the potential downsides (other than the obvious underhood dust/dirt in the engine bay) could be as well such as sloppy turbulent air or air not getting where it's intended etc but I still did it.