I could get rid of another 80 pounds and hit 3499 for an on track weight of 3699 with me in it and fuel, but it would be costly and noisy inside. Ceramic brakes up front -20. Rear door panels -16. BBS FI-R -28. Rear bench -16.
80 pounds is another big drop but that is a lot of money. The brakes might be worth the investment. As for the others the car still seems very usable right now. If you dont have too much noise inside thats more worth it.
I know I need a real diffuser, but in the mean time I hacked away some excess plastic where the mufflers used to be that was disturbing air flow or trapping it. Then I vented the rear bumper cover. Not really noticeable it’s so low.
http://i60.tinypic.com/155goj7.jpg
This part was squared off and sort of just hanging there, so I triangled it.
It actually might look pretty good if you cut that whole center section out from the stock rear valance and put some rs4 style mesh behind it.
This kit from Enlaes is probably the best in terms of eliminating rear lift. It’s pretty extreme for most people as it goes for that DTM look on a street car. But it’s very functional - it has the proper ramping and air guides. It extends a few inches beyond OEM to achieve this. The OE setup is too vertical and seems to be optimized for lowest possible drag, which makes sense.
http://i64.tinypic.com/wuo2l3.png
I think filling this front section with sculpted foam or whatever would actually help reduce drag and force air where I want it to go. With the OEM supercharger heat exchanger which was short and on the bottom, this design element was more important. Now that I have the APR heat exchanger that is really tall, it’s not necessary.
I wonder if covering the area between the bumper cover and the spare tire well would improve airflow out the rear.
I could probably remove the heat shield and reverse it to cover the gap. Logically this would form a 3 sided box against the rear wheel liner, which is just hanging there.
Without a big muffler in there filling that cavity, it’s likely just generating turbulent air.
at what point would it just be easier to remove the rear bumper on a track day. Took me 15 min to take mine off the first time, its amazing how simple it is.
I don’t think the whole cover has to come off as there’s still a rear bumper under the shell. Two questions:
1/ Should I use a utility knife to remove part of the rear fender liner pictured above?
2/ The spare tire well is sort of useless to me. I could relocate the lithium battery, weld that whole thing off, and install a flat plate on the trunk floor.
u can do all those things. and they will make a difference.
the question is what crazy high speed track you are going to where this is going to matter.
Mosport is the fastest track in the ALMS series and if memory serves, is the 3rd fastest track in the world.
I frequent there and even then on a street audi, I’m only avging 93mph.
But anyway, FWIW, if you are going to cut away the wheel liner…yes, it makes sense to do. You should weld the floor flat and per previous recommendations, straight up remove the bumper cover. Because once you remove all those things, your cover is still catching a whole lot of air.
AND if you’re going to make it so flat, you may as well do a proper diffuser (read: not enlaes). AND, if you want your diffuser to work, you will need to drop your ride height substantially…which is going to require firmer front spring rates to keep the travel in check.
I’ll start with the wheel liner and consult my shop about the best person to do the spare tire well, if I choose to go that route. The bumper cover is obviously sitting on top of the metal crash bumper beneath it. This appears to be structural to me. It doesn’t seem it would be necessary to pull the bumper off, rather you can just vent it below and possibly above. It’s actually set up pretty nicely right now with a flush tire well and bumper cover bottom, except for that trim silver piece on the rear valence which seems to be there to optimize for low drag instead of letting the air travel up. I agree the Enlaes piece doesn’t make sense after looking under the car.
My goal here is to 0 out rear axle lift on 90 MPH - 130 MPH pulls. While I could technically fit an off the shelf diffuser between the exhaust bends, I’m unclear that is necessary for reasons you mentioned. I’m not changing the ride height of 25.5 fender to ground.
On a side note, I realized the rollbar is acting as a rear tower brace because of the V shape that ends at the trunk floor and wheel well joint on either side. Will be good to get the front firewall brace in.
[quote=“westwest888,post:50,topic:7794”]
You don’t have rubbing problems up front at the track being that low? Mine’s 1/8" higher in the front than yours with non-aggressive 19X8.5 ET38 wheels with 255 tires, and if I take a fast sharp turn on a bumpy road, it will rub. This made me think this was too low for the track.
https://c1.staticflickr.com/1/593/21550628290_35b66ea85f_k.jpg
No rub on this. Just run a ton of camber.
http://i67.tinypic.com/1z3osk5.jpg
looks good west
Thats actually a great idea. If you can make it look right that would be a big help. Wonder if it would show too much under the car
Nice West! Maybe its just the camber, but it looks higher than 25.5" FTG.
Your instinct was right. I just found the sheet. It’s 26 5/16 in front both sides, and 26 1/4 both sides in the rear.
IMO, this is the perfect height for this chassis.
https://grassrootsmotorsports.com/articles/downforce-sorcery/
This seems kind of lol but is actually close.
Had to take the rear diffuser off Dad’s F430. Curb damage by the old guy. Notes…
it’s really strong and heavy, 15-20 lbs, FRP construction
if the entire flat bottom is made of this it must be 70-80 lbs total (the front FRP for sure)
It definitely takes a lot of space in the area. And a very nice wing profile.
http://images.tapatalk-cdn.com/15/11/09/e1148d14077d7e097e64dcab80630131.jpg
http://images.tapatalk-cdn.com/15/11/09/1f28a9724e1f851a3ab714a9d9bcc509.jpg
http://images.tapatalk-cdn.com/15/11/09/e30922cc7be9dab4ffdc04c90dd14236.jpg
http://images.tapatalk-cdn.com/15/11/09/5f8afd79400e5e890b3323655808e1e0.jpg
Wow I bet thats not a cheap part to replace.
Yup there we go. That’s what a legit diffuser looks like 
Not that enlaes stuff!
I like the nike swoosh on the diff cover hahaha