[BrianMN]

**UPDATE 3/18/12****

See post 33 for Testing updates!

In summary, testing shows the downforce of this underbody system compared to stock are:
70mph- Delta of apx. 302lbs- tested and confirmed
85mph- Delta of apx. 473lbs- tested and confirmed
100mph- Delta of apx. 543lbs- tested and confirmed
140mph- Delta of apx. 746lbs- extrapolated projection

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Hey Guys, Since the Tracking section doesn't get much traffic, I figured I"d post here as well.

So my car has been a very reliable and fun daily driver and weekend track car...to the point I would say it one of the best platforms for a DD/Weekend Warrior.

This next year will be much more focused on Track events and less on daily driveability...I'm registered for NASA TT-A (unfortunately the fastest class..Ill likely get less-grippy tires to shed some points) and will be doing quite a bit more competitive events..(Red Line TT, Super Lap Battle, etc)

The car is a 2008 E90 335i...on the street it has 440hp/500tq; however due to heat and snail-sized snails, it is capped to 300/300 for the track. (which also keeps points/class down) Suspension is fully setup with ASTs, good control arms, alignment, etc. The main things that are seperating this car from being a full-on track car is 1) Full-on Role Cage/completely gutting the interior and 2) Complete Aero system.

Since it is still a DD and I don't intend on it being a dedicted track car, I'm not concerned about a roll cage at this point.
So that leaves the Aero system. I’ve done a LOT of extreme-learning over the past month or so and have a complete new understanding of the complexity of aerodynamics when applied to cars; sedans in particular.

In short, the goal with any track car is to:
1) Reduce drag… including making the front as concise and smooth as possible, limiting the amount of air that is allowed under the car, making the body streamlined, and reducing the Flow Separation/rear vacuum created by the car’s wake.

2) Increase Downforce…this is the fun part. Most of the downforce will be created by low pressure underneath side of the car; with the fine tuning of wings, Canards and air dams.
The underbody should be made up of 4 Pieces: Splitter, Undertray, Side Skirts and Rear Diffuser. The most important thing to keep in mind with all of this; is that everything works as a system. None of these pieces alone will achieve high results unless they are all in place and functioning properly.

Splitter- There are 2 benefits of the front splitter.
1) To split air. Duh. This is the lowest, level piece of the front of the car; the choke point for the air to get underneath. This reduction of air is noticed throughout the entire underbody. Not only does it simply reduce it…but because of the smooth undertray it is accelerated. According to Bernoulli’s Principle, Accelerated air = lower pressure. Lower Pressure beneath = downforce. The lower it goes; the better the car blows

2) To provide real-estate for the high-pressure air that is created by the front bumper pushing through the air. The airdam (piece right above the splitter) essentially blocks the air; and the high pressure pushes down on the splitter.

splitter3 by MDM Enterprises, on Flickr


splitter2 by MDM Enterprises, on Flickr

splitter1 by MDM Enterprises, on Flickr

Underbody Smoovness- This is pretty self- explanatory. Many cars today come with semi-smooth belly pans; but anything rear of the transmission is bare and bumpy. Any open areas, exhaust channels, subframes/control arms, etc. create turbulence. This turbulence slows down the air, creates drag and minimizes the effect of the system.
**It is important to note that the underside of the car does serve another purpose: To extract heat from the engine bay. There is very high pressure in the engine bay from the incoming air; and it can only go through the gap between the hood and windshield (also high pressure), or flow backwards around the transmission and out an opening in the underbody. Because of this I’ve left open the area behind the transmission and front of the exhaust tunnel. The extra low pressure of this whole system should also help extract more heat.

underbody3 by MDM Enterprises, on Flickr

underbody2 by MDM Enterprises, on Flickr


Diffuser- This puts the “rice” in “Hey, look at that ricer”. Whilst it may end up looking like KTran’s NSX, the gains to be had from it are incredible. The basic goals of a diffuser are to utilize the expanding area to slow down the air and not increase pressure, so that when the faster air under the car meets the slower air on top of the car, less Flow Seperation (Vacuum bubble) occurs…which reduces drag.
The angle of attack for the diffuser should be adjustable from 6-15*; with 9.5* being seen as “ideal”. Thankfully my design just happened to be adjustable in that exact range
The design of my diffuser was VERY much controlled by the exhaust muffler and tips hanging down. For practicality’s sake, It would have been ideal to have the rear diffuser flat across,and span the width of the inside of the entire car, and be fenced off inside of the rear wheels. If it weren’t for the large muffler; I’d be able to use a better starting height and slow down the air even more. So this forced me to do a 3-piece design, which has two static sides (behind the rear wheels) and one center section under the muffler which is adjustable.


diffuser4 by MDM Enterprises, on Flickr

diffuser3 by MDM Enterprises, on Flickr

diffuser2 by MDM Enterprises, on Flickr

diffuser1 by MDM Enterprises, on Flickr


Side Skirts/Fences. Now if the splitter, diffuser and complete underbody were setup, then that would create very low pressure underneath the car. …however that low pressure would instantly be balanced by the atmospheric pressure outside of the underbody… eliminating any real benefit of this aero system. Because of this, it is important to “fence” off the underbody so that the low pressure stays inside where it belongs.


Side skirts1 by MDM Enterprises, on Flickr

side skirts4 by MDM Enterprises, on Flickr

side skirts2 by MDM Enterprises, on Flickr

side skirts3 by MDM Enterprises, on Flickr


*One important note is that the car will be roughly 1-1.5" lower in for the track; so whilst the side skirts don't look low now..they'll be much lower when it comes time for them to be useful.

To test this I"ll be working with a local Audi guru, who happens to be an Aerospace Engineer with access to some pretty cool [expensive] testing equipment. This will be able to accurately determine where pressure is dropping and where the air is flowing best/worst.

All in all; I am hoping this aero system will convert the ~150lbs lift into 500lbs of downforce at 100mph. I will definitely update this as I collect data and have some experiences on the track!
Thanks for reading,
Brian

[catch]

interesting...

[N0OS3]

^ i agree... interesting... i was thinking about picking this old '91 Camaro and making that my track car... i like fast bimmers, but i don't see myself putting my DD on the track more than a few times.

[TurboBimmer]

Very interesting!

But IMO there's no way you can get 500lbs of downforce on this car. The M3 GTS with its huge spoiler on the bootlid gets merely 30kg of downforce in the rear (7kg in the front) at 200km/h, as measured by german magazine SportAuto.

[BrianMN]

Originally Posted by Autobahn335i

Very interesting!

But IMO there's no way you can get 500lbs of downforce on this car. The M3 GTS with its huge spoiler on the bootlid gets merely 30kg of downforce in the rear (7kg in the front) at 200km/h, as measured by german magazine SportAuto.

?? I find that very hard to believe that a GTS that little downforce. A good wing alone will provide 1200nm/300lbs/136kg. I believe I've read that a stock M3 has zero lift and zero downforce; so any improvement in aero will be significant.

In any case, an M3 GTS with little downforce is quite hard to believe...do you have the link?

Cheers,
Brian

[TurboBimmer]

Originally Posted by BrianMN

?? I find that very hard to believe that a GTS that little downforce. A good wing alone will provide 1200nm/300lbs/136kg. I believe I've read that a stock M3 has zero lift and zero downforce; so any improvement in aero will be significant.

In any case, an M3 GTS with little downforce is quite hard to believe...do you have the link?

Cheers,
Brian

Here's a link, in german:

http://www.sportauto-online.de/bilde...toshow_item=16

Under the picture they mention 64 newton for the front and 290 newton in the rear.

Maybe there are different methods to measure downforce?

[BrianMN]

Originally Posted by Autobahn335i

Here's a link, in german:

http://www.sportauto-online.de/bilde...toshow_item=16

Under the picture they mention 64 newton for the front and 290 newton in the rear.

Maybe there are different methods to measure downforce?

Ohhhhkay; I had a different car in my mind. That is just a regular M3 with a little front lip and a tiny wing. I'm surprised it even created that much, to be honest.

-That wing is not in a place to do anything significant. Whilst the E92 coupe does not have a steep rear window, it is still suffering from detachment and that wing is by no means in clean air. Plus, that wing is ridiculously small.
-The front lip won't provide a huge gain over stock.

Like I said; this needs to be a complete system; and the M3 GTS in the above article has 1 of the 4 pieces....the small lip on the front bumper. The REAL downforce comes from under the car; which is practically untouched on that car.

In reality, changing 150lb of lift into 500lbs of downforce really isn't that big of a goal; however I won't get my hopes up until I see the numbers for myself

[Syndicategt]

Good luck with the project. May I also suggest some real brake ducts to cool those puppies off, as our "brake" ducts do practically nothing other than blow air over the tire. You should get with MFlow, appears his car has some aero work done.

[BrianMN]

Originally Posted by Syndicategt

Good luck with the project. May I also suggest some real brake ducts to cool those puppies off, as our "brake" ducts do practically nothing other than blow air over the tire. You should get with MFlow, appears his car has some aero work done.

Thanks. I do have real brake ducts setup; however I don't have the nice rotor hats like these:

http://www.stealthauto.com/Products/...205_f1227_2208

Right now the aeroduct hosing is just pointed towards the center of the rotor; and simply ziptied to the LCA.

I must say, these brakes are quite phenomonal for stock.

With DTC70 Pads/Motul 600 fluid, I never got [significant] fade with Nitto NT01s, NT05s or Yoko Advan R888s. It was only once I went up to Hoosier R6 and now the Continental Non-DOT slicks that I actually have more tire than brake.

[will.c]

Wow.. Very enlightening! Thanks for posting this. How did you study this? By yourself?

[Eric335]

very very awesome(: im jealous

[ichi_ban]

Looks amazing! I was wondering when there would be a real diffuser installed on a E9x

[BrianMN]

Thanks for the kind words, everyone

Originally Posted by wonho

Wow.. Very enlightening! Thanks for posting this. How did you study this? By yourself?

I have a good knowledge base of aerodynamics (and studied a LOT before building this) and am now working with a local Audi guru who just happens to be an Aerospace Engineer with a bunch of [crazy expensive] testing equipment. The information we're able to get will almost be better than 100mph windtunnel testing.

Originally Posted by Eric335

very very awesome(: im jealous

You might not have to be jealous for long if the production plans actually happen

Originally Posted by TeamSoloE93

Looks amazing! I was wondering when there would be a real diffuser installed on a E9x

I was quite surprised as well that nobody makes a 'proper' diffuser for these cars...it isn't tremendously difficult. As mentioned in the first post, much of the design is determined by the exhaust system.

My next steps with this are:
1) Make the a 3-piece mold of the rear diffuser out of carbon fiber (entire diffuser, mounts and strakes will be made of 3 pieces: 2 sides and one center)

2) Lower car to track height (Splitter being 3.75" off the ground) and conduct extensive pressure and airflow testing to determine how much downforce is created where.

3) Build underbody system (splitter, side skirts, underbody, diffuser) for another local E90 335 with dual mufflers

4) Build underbody system (splitter, side skirts, underbody, diffuser) for another local E92 M3 with dual mufflers

If this all goes well; I might be looking at marketing this to the E9x enthusiasts First I need to get hard facts and figures to show this actually does make a substantial difference.

[datbimmerdoe]

holy fuck'n shit in my pants!! this's epic! i commend u sir, wow.

[BrianMN]

Originally Posted by the infamous...

holy fuck'n shit in my pants!! this's epic! i commend u sir, wow.

Haha thanks; I'll hopefully have some pictures of the updated versions I'm working on soon

[royalblack888]

im in the process of DIYn my own :P

[tanginaglaz]

Amazing! any updates? I would like to do something similar.

[Doyle]

Very interesting.

I wonder if with some rear exhaust work you would be able to get a more integral diffuser of the m-sport "diffuser". Similar to what platte forme did with the e92 m3 rear diffuser.

I've been toying with the idea of grabbing the front bodywork off a junked e90 m3 and grabbing a platte forme or apr pre-manufactured splitter/under tray. That way I get the additional benefit of running wider front tires. If this works out, I may be persuaded otherwise.

Keep us updated!

[BrianMN]

Funny timing, as I had the chance to borrow a Stock (lowered) E90 335i last weekend for baseline testing. Not only does this underbody system show [much] lower pressure rear of the transmission, it also shows practically no turbulence compared to the stock E90. I learned quite a few interesting facts about the underbody aero of the E90 and will be making a comprehensive post after this weekend when I complete the testing on my car.

I've posted below simple screenshots of the *summarized* data collection from 90mph (in mexico). I originally anticipated doing all testing at 100mph, but Johnny law is out in full effect, and choosing to run hours at 100mph is just an option where I cannot afford the potential consequences. I do have quite a bit of data from 70mph- 130mph for specific data points, but the sample rate is too low to publish them as conclusive.

In any case, here is the summarized data from the test cases where there were ideal conditions.
-Windspeed 0
-Both E90 Pre-LCI, at same ride height, same wheels, same size tires.
-Stock E90 = Stock exhaust and stock control arms
-Mod E90 = M3 front control arms, stock rear control arms

*This data was taken from 26 data points from the first couple test sessions. I now have over 45 data points on my car for this weekend


Underbody Aero- MDM System Design2 Data2 by MDM Enterprises, on Flickr

Underbody Aero- Stock by MDM Enterprises, on Flickr

Without going into deep deep detail and long explanations of equations, I'll suffice it to say that the Underbody system is producing the following characteristics.
Rear of the Car- Delta of 350lbs of downforce at 90mph
Front of the car- Delta of 300lbs of downforce at 90mph

Cheers,
Brian

[cole92]

When I tracked my evo, I had a very similar looking setup. Looks great and numbers look good too!

[just4kickz]

you b needing new wheeels

[BrianMN]

Originally Posted by cole92

When I tracked my evo, I had a very similar looking setup. Looks great and numbers look good too!

Thanks! My buddy owns/drives the Gates311 EvoX and we built a diffuser for that car for it to run the Texas Mile last year....however that diffuser looks like crap compared to this one haha

Originally Posted by just4kickz

you b needing new wheeels

Haha yes, this was my winter setup. Here's a picture of the summer (non-track) wheels:


M3 wheels7 (1024x683) by MDM Enterprises, on Flickr