aftermarket aero for B8

B8 S4
#21

West, if you want to reduce lift, remove the rear bumper.
The bumper skin and how it curves down is actually catching a lot of air and causes rear end lift.
Removing it will solve for this. Even better if you can remove it and stick a diffuser under the rear diff so that the air is cleaner.

No need for crazy wings.

http://i1293.photobucket.com/albums/b596/GlobalTimeAttack/2014%20GTA%20Road%20Atlanta/Tony%20Parrish%20GTA%20Road%20Atlanta%202014/DSC_4657-3239565538-O.jpg

http://i280.photobucket.com/albums/kk178/futuretec/The%20Ones%20That%20Missed%20The%20Spot%20Light/MazdaRX-7FC3SR-MagicDemoCarBack.png

You’ll notice some drag cars have drilled out rear bumper skins too. It’s also done for this reason.
Though real talk - i havent gone under the car to look at how the rear bumper skin and diffuser hang downward from the chassis. Take a look to see how bad it is.

On some cars, like the current FRS, the rear muffer is designed to be an aerodynamic component so that the muffler itself acts like a ghetto diffuser and keeps air from separating and caught by the rear bumper.

#22

Yes, great points boro to further this discussion…and I didn’t know that about the FRS.

#23

http://images.tapatalk-cdn.com/15/09/07/a3045c5d36b98e7857a9425a7b85b530.jpg
I’ll have these guys make a diffuser and test it out

#24

Would adding a bottom cover to the back like you see in the front by the oil pan and transmission do the same thing if you made them meet at the bumper level

#25

So im assuming that a real splitter/aero runs from the front all the way to the back for the reason of not creating lift/drag underneath the car to the rear bumper correct? Thats why it should be one piece?

#26

Let’s make a distinction here guys.
There’s under body aero to reduce drag (ie: flat under trays - which the B8 has to a degree), and then there’s under body aero to create downforce (diffusers).

A flat under tray from front bumper to rear bumper is just that - it’s a flat panel intended to smooth out airflow under the car. It doesn’t have any significant downforce advantages. If you want downforce, you add a diffuser.
What’s the difference? A diffuser creates a pressure zone where air is accellerated out from under the car and sucked up to a higher area, thus pulling down the end of the car where this occurs. A proper diffuser must be at a specific length and specific angle in order to function appropriately. The type of thing you see today that most people slap on the back of B8’s don’t do anything meaningful.

pic of “real” diffuser:

https://s-media-cache-ak0.pinimg.com/736x/13/31/68/133168ce660a8ae0dc91d5bfe02eee95.jpg

The location of where the diffuser begins to kick up, the length of the kick up and where it is placed under the car all has affects on how much downforce it generates, and where the downforce is applied on the chassis. You can get some software to model this and estimate the affects

http://www.miataturbo.net/attachments/race-prep-75/65741d1359266985-miata-flat-underbody-img_2346.jpg

you pretty much have to cut the rear bumper skin to run something like this

#27

Cool. Thanks. I love learning about this stuff.

#28

I’ve been doing some reading on this topic. First, the mod bargains splitter will have the effect of removing the slope at the front of the car, properly damming up the air. This is still a street legal car and I don’t have a front axle lift system like the GT3 and the new 991.2, so I can’t be 3" off of the ground. I want the mild effect of beginning to create a high pressure zone in front of the car at 120 MPH.

I didn’t realize until now that the wheel wells are high pressure zones (that lift the car at speed). By directing air behind the wheel, you can turn it into a low pressure zone which actually helps evacuate heat from the engine bay. The driver’s side fog light hole and intake ventilates into that wheel well. On the passenger side, I may remove more of the blocked airflow. I realize this is optimized for low drag. I don’t mind trading off a small amount of drag for downforce on the front end. If I cut a vertical slit in the passenger side wheel liner, air will flow behind the wheel from the fog light vent.

The rear of the car is raked quite nicely for evacuating air as you can see in the photo below. The Milltek exhaust has no rear mufflers further streamlining what would otherwise be turbulent airflow.

The trunk spoiler is doing it’s job. A roof spoiler would just ruin that airflow and create drag, so we’re not doing one. The S4 has a small advantage over the S5 here, where the trunk creates a nice long surface for downforce. Of course the RS5 active aero is the best of both worlds - no drag at low speed and downforce (removal of lift) at high speed.

The canards on the front bumper of cars like the GT3 RS are pretty awesome. They are supposed to send air around and over the wheel wells. On most cars if you install them aftermarket they will spider the paint as the body work bends at speed.

Some of the drag reduction effort is ridiculous as we run HPDE with the windows down in case the car rolls. But I’m not about to install wind deflectors (for people who smoke cigarettes in the rain) on the side windows.

http://i57.tinypic.com/axe0lc.jpg

#29

I’m basically 150 HP away from this outcome.

http://roa.h-cdn.co/assets/15/13/980x490/landscape-1427555426-screen-shot-2015-03-28-at-105151-am.png

Also, this is an extreme example of racecar aero on a concept car.

http://icdn4.digitaltrends.com/image/ferrari-f80-concept-024-970x548-c.jpg?ver=2

#30

If your lip is not bolted to the chassis, it isn’t doing anything meaningful. A real splitter creating the pressure zones that you speak of can support your body weight and then some. Stand on one of those cf ricer lips and it will simply crack. Sure, maybe a lip will get you 5lb reduction in lift. Maybe it’s a really good lip and can do a 30lb reduction in lift. Neither is something you will feel in a modern car, and will not have any affect on lap times. You want real aero, get some plywood and do this:
http://image.sportcompactcarweb.com/f/8994861/0707_sccp_16_z+project_miata+splitter_mount.jpg

Look at the e36 m3 ltw for a factory example of how true front end aero is achieved. The ltw splitter is adjustable in length for downforce tweaks and is bolted right up to hard points on the chassis. Not some double side tape job to a bumper skin

#31

With all due respect, I don’t think you need to be bolted to the chassis to negate lift at 120 MPH. I’m not trying to support meaningful downforce at that speed with this surface. Mostly I just want to push some air up into the front air openings or over/around the car, instead of under it. I’m not going to lower the car 1" for like 5 reasons, but I can afford to remove some ground clearance without scraping.

If you’re going to literally lever the car with an 10" lip, then yes it must be bolted to the chassis and it has to pass the test of someone standing on it. A lip must be twice as long as the car is high off the ground. The 991 turbo S has the active rubber lip on front. I’m doing the same thing but fixed.

https://scontent.cdninstagram.com/hphotos-xfa1/t51.2885-15/s320x320/e15/10467722_1439563809653333_1182325045_n.jpg

#32

West, I hear you on that.
That’s why I said a lip can even do like a 30lb lift reduction. But whether or not that is going to make any meaningful affect on lap times and driver confidence is up for debate (I am leaning towards no - 30lbs at 120mph makes no difference on lap times).
Comparing a mod bargains splitter to a porsche engineered solution isn’t really fair, but also, tacking on some form of aero to a car to cause a measured change also isn’t a crazy thing to ask for–so i get where you’re coming from. Simply tacking on a duck tail on the back of the car has meaningful affects, so a lip of decent size would make a difference too. But again, whether it affects how the car drives is a whole other matter.

Do it if you think it looks nice. But you’d be kidding yourself if you bought a $700 lip with hopes that it’d make a change that you can feel. I just doubt it really would–even if the change was a lift reduction of 30lbs.

If you were after some meaningful body work mods, I’d personally invest in an RS4 front end if I were you - and use the extra air opennings available on the front bumper to duct air to the brakes. That’s the biggest thing to solve for on the S4 IMO.

#33

^ Sound advice, boro92.

  • rep
#34

It’s really just fine tuning. The coarse adjustments have been made. The car is essentially done, unless I decide to use Brembo CCM-R ceramics when I need new discs about 14 months from now. Otherwise, not much is changing.

The only effect I want is to let the suspension do its work without the body being lifted higher than I set it, by air. I did make the car 350 pounds lighter than Audi engineers sent it to me. 120 MPH might create more lift in my car than a stock S4, because of the weight difference.

#35

Sliced out the bottom 1/3 of the passenger side front vent. Above that is the water pump. I’ll slice the wheel well felt in the back to let the air that goes in escape. The fog lights are out and the wires tied off. This should sort of make the front overhang into a lip spoiler, which is already well secured to the car.

http://images.tapatalk-cdn.com/15/09/11/e50ccf5e40bc58029a21b49c7fee3778.jpg

#36

Relevant

http://images.tapatalk-cdn.com/15/09/11/0d49a38d8ec0f786b61f15ebe9d763be.jpg

#37

Just saw this on Jalop:

http://i.kinja-img.com/gawker-media/image/upload/s--x0KbfBwn--/c_scale,fl_progressive,q_80,w_800/1427419447836423714.jpg

http://blackflag.jalopnik.com/an-aston-martin-with-a-dinner-table-hanging-under-its-r-1730267827

#38

Underbody vortex generators are cool.

http://blog.caranddriver.com/aerosmithing-how-the-ferrari-488gtb-makes-the-air-its-ally/

#39

The 991.2 has active front valence aero, where the flaps open at high speed (at 75 seconds into the video).

https://www.youtube.com/watch?t=75s&v=wx_YYgq0rvE

#40

350 pounds. Thats no small amount. and you added the roll bar