All,

pfunk's posting on this forum regarding new products from Japan has got me thinking again about potential improvements in MINI's aerodynamics. I know nothing and wonder if anyone has any knowledge about this huge topic, and would be willing to share with the rest of us. Am hesitant to post this question on the EXTERNAL MODIFICATIONS forum for fear that the performance oriented readers won't look there.

I know that aerodynamic modifications can potentially improve "down force" and the drag coefficient (efficiency thru the air) of an automobile. I also know that there are a few after market products out there that are purported to improve "down force" and such. But I don't have enough knowledge to separate the wheat from the chaff.

Specifically, I have been thinking for a year about building a smooth under the body panel for MINI that would enclose the bottom of the engine, exhaust system and related body hardware and maybe reduce the drag underneath the body at track speeds. Am reluctant to embark on such a project without a better understanding of what is actually needed and what is possible in terms of a performance improvement.

A bit of an experiment I had already built a version of the "wing" depicted by pfunk in his post. My logic was to extend the width of that stock little rubber "dam", the "L" shaped rubber piece that is bolted underneath the front subframe rearward of the engine, to the edge of the body. Don't know the purpose of the stock "dam" and cannot actually say what if anything my extension has added to MINI's aerodynamics on the track.

Can anyone help?

Regards,
John Petrich in Seattle

 

...John, if you can make the air pass under the car faster than above, down force will be aided, but as well, you'll need more power to over come this aero friction. I believe in this strategy more than air dams for example as these add down force while also adding surface area. Aero (cd) is defined by shape and surface area. Remember Collin's Lotus that was banned after its first race? Absolutely devestated the field!

I've also thought about a louvered hood as well as louvered front fenders. Lots of work...not all of it snow and salt worthy...outside rear view mirrors are also an insult to the wind...I wonder about the viability of the stock MCS rear spoiler; an aid or aero cliche?

Unfortunately, some of the aero subtleties are born from wind tunnel testing.

A big question in my mind would be, at what speed do you want these improvments to work? I would be willing to perform some research and talk with folks I know in the racing profession. This is a tall task my friend.

Michael

 

 

To my knowledge the Mini has the same drag coefficient as the S2000....which you wouldnt' think by looking at it...so..it's pretty good ....not that there isn't room for improvment on anything....just letting anyone whos interested know

the minis being .37

and on way to lessen drag would be those little carbon GT mirrors....they are not my thing but they would help quite a bit

 

From what I understand, drag coefficient doesn't really mean much. The drag coefficient needs to be multiplied by the frontal area in order to get a true apples to apples comparison. The G35 sedan has a drag coefficient of .26 with the aero kit. That is EXTREMELY low. Given that, it still has more drag than say an S2000 even though the S2000 may have a higher drag coefficient.

I think that magazines have just magnified this number and haven't given the true drag of the car. I have seen a few magazines that show the frontal are of the car as well as the Cd.

 

Thanks meb, Tuls, and D Nyholm for your input,

Specifically, I am interested in improving MINI's straight-a-way speed at the track and, maybe, improving MINI's dynamic stability in the higher speed track turns. Don't expect much improvement for street driving or improvement in gas mileage. Don't know if aerodynamic mods will help?

The obvious low hanging fruit could be front air dams, (to reduce lift at high speed), a smooth underbody panel (to reduce under the chassis air drag) and maybe some sort of a rear under body extractor system (to create a little down force), and aerodynamic mirrors.

Took a long look at the new Lotus Elise, yesterday, as a likely good example of modern auto aerodynmic engineering. I didn't see a front air dam on that model. The Elise did have a full body length smooth under body panel and did have two generous extractor ducts in the rear bumper, each side of the exhaust tips. The mirrors stuck out like two huge ears. Of course, the Elise presented a very small overall frontal profile. The MINI to me, by contrast, has all aerodynamic appearances of an outhouse. Okay, okay, the Cd numbers might be pretty good, but it sure seems clunky looking.

At my end, will work on the underpanel first. Am purchasing some aluminum this weekend.

Does anyone know the purpose of those 5 or 6 short stubby rubber pieces that are bolted to the undercarriage of MINI? I suspect that they are there to control underbody air flow; slow it down or deflect it ???

Interested in people's input,

John Petrich in Seattle

 

Well, the underbody pieces are probably some sort of diffuser to get some of the air out from under the car. I haven't looked at them though so I can't be sure. Going back to the G35, there is a few underbody pieces that come with the aero kit that are just plastic panels that bolt up underneath the car. They redirect some of the air and help reduce lift at speed. With teh kit, the G35 has zero front and zero rear lift at speed. Without the aero kit, the car has zero front lift, but not zero rear lift.

I think a flat underbelly will really help the car out at speed. Making it more stable. The only thing I am thinking of is that you will make the car more of a 'wing' (airplane) that way. Just the way I am thinking that lift works....the air over the car will have to move faster in order to meet back up with the air that went under the car creating less pressure at the top of the car, in turn causing more lift. Is that the correct thought process?? I would assume you'd lose enough drag that a rear/front wing will help with the downforce while still not adding as much drag as the underside would create.

 

Yeah you got the correct line of thinking concerning lift. I was puzzled too as to why people put flat underbody panels to increase downforce. This is just like an airplane wing, actually creating lift! Basically flat underpanels creates smooth airflow to reduce drag. The smooth airflow also benefits other aero bits that create downforce (front splitter, diffuser etc).

Also wondering if anybody has done this. Intersted in doing this myself and just want to see what is involved.

 

Smoothing the underbody flow increases the flow speed, but don't forget about the ground below the car. If you get the back end right, you get a Bernoulli-type flow, which creates some suction and draws the car down. That's why you usually see some sort of diffuser at the back end. You're not going to get much "wing" effect.

I noticed the little deflectors just ahead of the wheels. They're there to create a vacuum, which helps efficiency somehow (not sure, but all the exotics are doing it). I added them to my last car (a WRX) and felt some improvement at highway speeds, in that there was somewhat less turbulent action and the car tracked a little better.

We could probably benefit from a good front splitter. There's already a little bit of a diffuser at the back end, but it would benefit from being a bit bigger all around.

 

to keep the air out from under the car. But remember, the IC scoop puts air into the engine compartement, and the only way out is under the car. Making the bottom smoother and excluding air are good, but you want extraction out the back, as someone posted, to "suck" the air out from under the car, and also give a way for the air from under the hood to get out.

I read that the GP used some underbody stuff.... But I don't know for sure....

Also, for those of us that have modified the exhaust system (one ball or straight back exhaust), there are different flow constriants out there.

Also, the dams in front of the tires are to keep air from the tire wheel area, that is very turbulent....

Matt

 

Barnabas,

Here is a photo of my front and rear underpanels. Just large sheets of 0.060" T-6061 aluminum that I trimmed and shaped. The front underpanel attaches under the front air dam lip and terminates at the front sub-frame. The rear underpanel starts just behind the CAT and terminates infront of the rear wheels. No data as to what impact the aero underpanels have on MINI performance. Just have faith that a smoother undersurface reduces drag.

Regards,
John Petrich in Seattle

 

As luck would have it, the July issue of Sport Compact Car magazine has published the first in a series of articles about practical automobile aerodynamics. Those interested in this topic might start looking into these tech articles as they get published.

I feel that a number of their tech series are quite informative and authoritative. The magazine went thru a complete reorganization earlier this year and they haven't always delivered on their promises in the past on the tech series of articles. But, I will eagerly anticipate what ever they manage to publish.

John Petrich in Seattel

 

I'll have to check out that issue. The June issue was somewhat of a dud for me.

Here are a couple of links that I like for basic aero stuff:
http://www.mulsannescorner.com/
http://www.geocities.com/skoshiracing/Aerodynamic.html

I applied the "air boards" on the Skoshi racing site. They do show some of the cool old-school ways to check out your air flow, like tufting and gel.

 

"D",

Thanks for posting those sites. I'll spend some time reading them and doing some additional research. After I digest the Sport Compact Car article I may post some thoughts. Hope that you do, too.

Regards,
John Petrich in Seattle

 

You may want to angle the trailing edge of the front panal down a bit, and the leading edge of the rear panal up a bit, to keep air from getting above the rear panal and making a pocket.....

But this looks good. Also, you may want to put some dams on this (with a pop rivit too) that are angled that would shove some of the air out the side, and result in less drag under the car as well.

Matt