Aero question - vent wheel well liners?

[twistedneck]

Trying to lower the pressure around the tire so that it does not try to lift the car off the ground.

Usually you will see louvers on top of the fender or pathways and scoops in front of and behind the wheel well. On S197 front wheel well is plastic / sealed front and back and sealed up top by the metal bottom of the strut. see pic below. ignore the arrow.. pic credit to cjpony.

How about putting a vent in the rear plastic wheel well? goal is to reduce lift and drag.

http://www.superhachi.com/theory/downforce/

The wheel wells are another area where an undesired pressure differential can develop. Air flowing beneath the car stagnates on the tires, creating an area of high pressure. This effect is compounded by the brake cooling ducts that many teams use, which force even more air into the wheel wells. All of this air is also heated by the brakes, creating the same buoyant forces as in the engine bay. This high pressure area also exerts a drag force on the car. For this reason, many race cars and high performance road cars also incorporate vents at the top or rear of the wheel wells.

You can also see how the hood works in that same picture. I think its a good write up despite the homemade looking sketches.

 

[DGRacing]

Glad to see this. I've been thinking about this myself. I even bought some universal black fender louvers and might cut and mount them into the fender just behind the wheel well and in front of the mirror. Then create some kind of path from the well to the vent/louvre.

 

[twistedneck]

Glad to see this. I've been thinking about this myself. I even bought some universal black fender louvers and might cut and mount them into the fender just behind the wheel well and in front of the mirror. Then create some kind of path from the well to the vent/louvre.

Here is how Dave Martis solved it on the K&N S197 NASA Mustang.

http://www.motoiq.com/MagazineArticles/ID/3449/PageID/7575/Fully-Filtered-Dave-Martis-KN-Engineering-Ford-Mustang-RTR.aspx

I'm not willing to cut out the sides of my fender.. I'd like to put a grill in the front and rear plastic fender liners - not sure that would vent to anywhere productive, it seems the metal is directly behind the plastic so we would have to vent that also.

There is always the nuclear option of cutting holes near the strut to vent air out however that would compromise structural stiffness and could cause a major crack in the structure!

We could also add some sort of air duct to the top of the wheel well and vent that duct somewhere.

 

[ArizonaBOSS]

TBH I think you will do a lot of work for very little (if any) realizable gain.

That being said, one of the projects I'll be working on this year is making front fender "spats" that stick out around the front circumference of the wheel well to deflect air away from the 315 Hoosiers I'll be running soon.

 

[twistedneck]

TBH I think you will do a lot of work for very little (if any) realizable gain.

That being said, one of the projects I'll be working on this year is making front fender "spats" that stick out around the front circumference of the wheel well to deflect air away from the 315 Hoosiers I'll be running soon.

Those help prevent flow separation on the side of the car and that will reduce drag but it wont help the lift problem. However i do agree with you about return on investment since none of the world challenge teams seem to be venting their wheel wells or well liners.

 

[DGRacing]

Here is how Dave Martis solved it on the K&N S197 NASA Mustang.

http://www.motoiq.com/MagazineArticles/ID/3449/PageID/7575/Fully-Filtered-Dave-Martis-KN-Engineering-Ford-Mustang-RTR.aspx

I'm not willing to cut out the sides of my fender.. I'd like to put a grill in the front and rear plastic fender liners - not sure that would vent to anywhere productive, it seems the metal is directly behind the plastic so we would have to vent that also.

There is always the nuclear option of cutting holes near the strut to vent air out however that would compromise structural stiffness and could cause a major crack in the structure!

We could also add some sort of air duct to the top of the wheel well and vent that duct somewhere.

If you have the tiger hood you could maybe vent the well to the engine compartment somehow.

I agree that there is little gain here but with race cars I also believe every little bit helps. It adds up.

 

[DGRacing]

TBH I think you will do a lot of work for very little (if any) realizable gain.

That being said, one of the projects I'll be working on this year is making front fender "spats" that stick out around the front circumference of the wheel well to deflect air away from the 315 Hoosiers I'll be running soon.

I've been thinking of fabbing front fender lip deflecters that do this. Happy to compare notes. I want to design something that blends with the LS splitter.

 

[ArizonaBOSS]

I've been thinking of fabbing front fender lip deflecters that do this. Happy to compare notes. I want to design something that blends with the LS splitter.

Ditto. Probably won't get to it until April/May timeframe.

 

[twistedneck]

If you have the tiger hood you could maybe vent the well to the engine compartment somehow.

I agree that there is little gain here but with race cars I also believe every little bit helps. It adds up.

I'm wondering if a big hole covered by a louvered vent plate right behind the coilover front strut would do it? of course you would have to have the tiger hood to make that work.. The higher you could go with the vent the more it would work since there is not only a drag penalty from the high pressure air but the upward force vector from pressurized air.

 

[Grant 302]

Those help prevent flow separation on the side of the car and that will reduce drag but it wont help the lift problem. However i do agree with you about return on investment since none of the world challenge teams seem to be venting their wheel wells or well liners.

The spats that (I think) Drew is talking about should help kill a little lift too. Making the air follow around the top of the arch will have a downforce component along with creating a low pressure area that would suck some wheel well air out. These are some small ones I used to have on:


Many racers are restricted from doing such aero mods, or can be costly from a point count depending on the organization.

But back to the main topic...I think the more air you can vent from the fenderwell area, the better for killing lift and increasing engine and brake cooling.

One more effect that that *excellent* hand drawing is missing, is that air moved by the top of the wheel and tire is a turbulent mess and better off vented. Oh and btw, for those that didn't know, the top of your tire is moving at exactly TWICE the speed of your car. So when I round the ROVAL at 145+, the top of my tires is moving at 290+. So anything you do to help control the air moving at near 300 mph will help!

One other thing that many have not notices is that our fenders have a piece of foam/batt insulation/bulkhead thing toward the back just in front of the door. I pulled both of them out. Strangely, they aren't fastened by anything an they can be pulled out by hand intact. This allows some of the air to escape between the fender and the door and at the top of the fender by the cowl and A pillar. I'll try to find a pic of them later.

 

[302 Hi Pro]

One other thing that many have not notices is that our fenders have a piece of foam/batt insulation/bulkhead thing toward the back just in front of the door. I pulled both of them out. Strangely, they aren't fastened by anything an they can be pulled out by hand intact. This allows some of the air to escape between the fender and the door and at the top of the fender by the cowl and A pillar. I'll try to find a pic of them later.

I too have found this foam/batting liner in the rear of the Boss front fenders. The inner front fender plastic wheel well is also a two piece unit with front and rear sections. So, would removing the rear section of the front inner fender well liner as well as removal of the foam/batting liner help?

There is a weather strip that I remove for Track Days that runs along the bottom rear edge of the hood that hopefully helps to vent under hood air. It seals the cowl to hood area at the base of the windshield.

I also remove the small splash guard in front of the rear fender well opening at the rocker molding.

A few years ago, didn't Shelby American campaigned a 2012, (?), GT500, (1000 ?), for a 200 MPH run? I wonder if they felt the need to address this issue on their car. Anyone have knowledge of this SA 200 run project?

Just a few thoughts,
Regards,
Dave

 

[TMSBOSS]

You have to be careful when allowing air to enter at the rear of the hood.

Sounds strange but there is positive pressure at the base of the windshield. Removing the seal on the hood should add air to the engine compartment. Adding air at the windshield area when we are trying to remove air may be counter productive.

 

[Grant 302]

I too have found this foam/batting liner in the rear of the Boss front fenders. The inner front fender plastic wheel well is also a two piece unit with front and rear sections. So, would removing the rear section of the front inner fender well liner as well as removal of the foam/batting liner help?

There is a weather strip that I remove for Track Days that runs along the bottom rear edge of the hood that hopefully helps to vent under hood air. It seals the cowl to hood area at the base of the windshield.

I also remove the small splash guard in front of the rear fender well opening at the rocker molding.

A few years ago, didn't Shelby American campaigned a 2012, (?), GT500, (1000 ?), for a 200 MPH run? I wonder if they felt the need to address this issue on their car. Anyone have knowledge of this SA 200 run project?

Just a few thoughts,
Regards,
Dave

I wouldn't remove that complete back half. Otherwise the rear of the fender would become more of a parachute. I plan on making louvered/slotted holes and covering with wire screen to help keep the clag and gravel out.

I have the sides of the rubber seal out and left about a foot in the center to help stabilize the hood! Just don't leave it off all the time...I think the heat from the vented air is ruining the lower windshield rubber trim that's attached to the two plastic cowl halves.

You have to be careful when allowing air to enter at the rear of the hood.

Sounds strange but there is positive pressure at the base of the windshield. Removing the seal on the hood should add air to the engine compartment. Adding air at the windshield area when we are trying to remove air may be counter productive.

I've tested that it vents rearward, but that's with relatively open grilles like the 302S and Steeda. Not 100% sure how it would do with a stock grille but I suspect it would still vent.

I think the pressure at the cowl has always been a bit overstated. With the bulb seal in place, the cowl area has a lot of stagnation an is probably mostly turbulent to slight vacuum/drag at the rear facing surfaces.

 

[ArizonaBOSS]

The spats that (I think) Drew is talking about should help kill a little lift too. Making the air follow around the top of the arch will have a downforce component along with creating a low pressure area that would suck some wheel well air out. These are some small ones I used to have on:

Yep, that's what I'm going for, but probably an inch or two wider to meet up with the ends of the splitter.

Is there a product page that sells stuff like that already?

 

[Grant 302]

Yep, that's what I'm going for, but probably an inch or two wider to meet up with the ends of the splitter.

Is there a product page that sells stuff like that already?

I didn't find any for the front of the wheel wells.

I got some small sizes of black 'pebble' or textured finish ABS sheets from *bay. The one in the picture is 1/16", IIRC and I've been meaning to cut a set from 1/8" stock that I picked up which better matches the rear splash guards. Other thicknesses are widely available like 3/16", 1/4" etc. It's also not difficult to 'mold' a little bit into curved shapes in the oven if you need to.

I used sheet material like this:
http://www.ebay.com/itm/271491779238

 

[DGRacing]

Yep, that's what I'm going for, but probably an inch or two wider to meet up with the ends of the splitter.

Is there a product page that sells stuff like that already?

I looked high and low for a universal part that could be fashioned to work. No luck. But I'm going to contact a carbon fiber part maker that claims one week turnaround on smallish custom orders. We'll see!

But yeah. Wider.

 

[ArizonaBOSS]

I looked high and low for a universal part that could be fashioned to work. No luck. But I'm going to contact a carbon fiber part maker that claims one week turnaround on smallish custom orders. We'll see!

But yeah. Wider.

Let me know what you find out regarding sizing and cost.

 

[Roadhouse]

I made this splitter and wheel spat combo last year. It wasn't too hard to make but I've since cut it down and scrapped the spats since it seemed like a little too much for my car at the moment.

 

[Grant 302]

I made this splitter and wheel spat combo last year. It wasn't too hard to make but I've since cut it down and scrapped the spats since it seemed like a little too much for my car at the moment.

Too much for your car? Nah. If you weren't lifting the front tire, then maybe.

 

[ArizonaBOSS]

@roadhouse Yes, that is exactly what I'm envisioning.

How did you attach it to the fenderwell? Just use the existing two screws on each fender, plus the splitter attachment? Any other pictures or notes?