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Old 07-07-2010, 01:50 AM   #1 (permalink)
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2004 MINI Cooper S - Improving Aerodynamics

I've never posted here before, so this will likely seem totally out of left field, but I've been lurking for several months, and I finally started modding a few weeks ago.

The car is a 2004 MINI Cooper S (R53 - Supercharged) in British Racing Green, and for the most part it's completely stock. I replaced the ignition coil with an MSD Blaster, and I upgraded the plugs and wires at the same time. Aside from that, I've installed a PLX Kiwi MPG (about half the price of a ScanGauge), but I haven't yet gotten it calibrated properly, so the trip average mpg readout stays around 7.8 mpg, regardless of when I reset it and how I drive.

I removed the exhaust tips because they add weight (and possibly a little bit of drag) and serve no non-cosmetic purpose, and I replaced the long, wiry antenna with a stubby, rigid one. I also removed the rear spoiler, as the car is FWD and will likely never see more than 100mph (and that's only in case of emergency), so the downforce it might or might not actually provide at those speeds is pretty much irrelevant.

I started with the more radical mods a couple of days ago, and since then have achieved rough grille blocks for the upper and lower grilles (I'm leaving the hood [bonnet] scoop open), as well as extending the factory airdam a couple of inches lower (I decided on this instead of a full belly pan because it's way easier and AndrewJ went with the airdam instead of the belly pan and had great results). Anyway, I did all that with black coroplast.

I'm really terrible at fabrication, so none of it looks good at all, and I'm also very undisciplined about testing, so I'm sure I'm going to drive the hardcore aeromodders nuts. Nevertheless, I'm trying, and that has to get me a certain amount of credit.

I have a few more radical-esque mods planned, and ideas for a couple more:

The most significant area of drag for most hatchbacks seems to be the rear, which just kind of falls off, leaving a huge turbulent wake. While a full boat-tail is the best solution, this car is hopefully going to be a daily driver for another 2-3 decades, so I don't want to do anything TOO radical, and I definitely want it all to be pretty much reversible (I have a few screw holes that are permanent, but you'd have to look hard to find them).

That said, I'm planning a removable boat tail of some sort based around a strap-mounted bike rack (most likely a Yakima Megajoe). When we moved to Oregon, we drove from southern Illinois with the car completely packed, with a Schwinn cruiser on the back of the car. Those cruisers are massive bikes, and it stuck out on both sides of the car, as well as over the top, so the wind assault was brutal for a few thousand miles. Every night, we took the bike off and I checked all the straps, and none of them had loosened at all, which leads me to believe this thing is crazy sturdy, so it'll be ideal for mounting the tail.

Rear wheel skirts/fairings should bring measurable gains, considering the wheels and tires protrude past the wheel arches, causing all sorts of turbulence. I'm planning on mounting them directly to the body after removing the arch covers, and I'm thinking since there's hardly any bumper at all behind those wheels, I may make the fairings just a bit longer and create a slightly more permanent partial boat tail.

If you've ever looked at the front of a MINI, particularly a Cooper S, with its larger wheels, you've probably noticed that the wheels and tires poke out of the wheel arches just like they do on the back. If I can somehow extend the bumper to cover this, that combined with the rear wheel skirts should keep flow attached on the sides of the car significantly better than stock. The easiest way to do this might actually be the hardest, but I'm thinking if I have a large, curved piece to cover the entire front bumper, it can extend past the wheels, while serving as as an airdam, grille block, and front wheel fairing. Being that my fabrication skills are virtually none, I don't see this happening unless someone is willing to give me MAJOR hands-on help.

So, these are my plans. I'll have pics of the mods up once I've made enough posts, but pm me in the meantime if you want to check them out.


Last edited by iplaysdrums; 07-07-2010 at 02:10 AM..
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Old 07-07-2010, 11:02 AM   #2 (permalink)
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Well well! Very well written and well thought out! Welcome, enjoy your stay, and congrats on deciding to ecomod!

With wheels that stick out beyond the body, things get kind of feisty. The air dam is a great way to start off; with a car that low you may want to go to a belly pan later though.

If you don't want to go to a full tail right away, you can always start out by trying for a Kammback off the roof - that'll help quite a bit.

Do you have any measures of your current MPG?
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Old 07-07-2010, 11:23 AM   #3 (permalink)
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Time for before and after pics:









I think these are pretty self-explanatory, but if there are any questions, please let me know.
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Old 07-07-2010, 11:36 AM   #4 (permalink)
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To make rear wheel skirts you'd definitely need a stabilizer/shaper bar at the bottom of the cover, so that you can bow the skirt around the wheel. does the cladding/trim come off easy? I bet you could go right underneath it for mounting points and not have to put in extra holes.
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Old 07-07-2010, 12:39 PM   #5 (permalink)
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With the exhaust in the center like that you can fill in the low pressure wake by flooring it
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Old 07-07-2010, 12:58 PM   #6 (permalink)
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Switch the front grill cover to the inside instead of the outside of the grill.

You will get about 90% of the effect you have going right now but wil look 200% better (like stock). Thats how I did it in my Mazda to keep it clean looking... and you have a Mini Cooper it has to be clean looking!

BTW racing discs would look amazing on your car (very retro) so you could get away without making rear wheel skirts and again keep it looking clean and "cool"
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Old 07-07-2010, 01:39 PM   #7 (permalink)
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At the risk of belaboring the obvious, the Mini with its
plastic wheel arches looks to be a perfact candidate for
the water heater pan rear wheel skirt treatment.
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Old 07-07-2010, 01:51 PM   #8 (permalink)
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You're only an hour and a half away from me. If you want some fabrication help, just let me know!
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Old 07-08-2010, 11:16 AM   #9 (permalink)
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Thanks, everyone, for the positive response! I'll try to address everything:

I'm still having to calculate MPG the old-fashioned way (from my refueling receipt), because the Kiwi is thoroughly unreliable just yet. Supposedly I can calibrate it to make it more accurate, but finding the time and the inclination to get two people out on a straight where I can drive back and forth for a while, adjusting numbers... It's difficult, and I'm not looking forward to it. Like I said previously, I'm not much for rigorous testing, but I will get around to that soonish. Long story short (too late), The past couple of tanks have averaged in the low 30s, and that's mostly city driving. I haven't had a full tank testing the aeromods yet, and my mileage on the current one is ruined thanks to making sure the grille blocks won't cause the car to overheat.

I definitely agree that the wheel skirts will need a stabilizer, and the arch covers come off quite easily, providing access to pre-drilled holes, so that shouldn't be terribly complicated. I hadn't seen the water heater pan thread before, but I'll definitely look into it.

My wife agrees that we should keep a clean look, so I took the upper grille block off last night and replaced it with tape behind the grille. It's heavy-duty high adhesion tape used in an optical lab (I make glasses for a living), and this particular tape is from a different type of lab, so I can't actually use it in mine, which makes it perfect for use on the car. I haven't had a chance to test it yet, but it certainly looks 1000% better, and it's much more airtight than the coroplast block I had on there yesterday. I'll try to get some updated pics up in the next couple of days. As far as the lower block is concerned, I'm thinking about using the same tape and just covering the whole bumper. It'll still look pretty clean, as it's clear tape, and that will cover the foglight openings as well. That will probably happen tomorrow.

I don't think I'll ever go to a full belly pan or a traditional full boat tail (permanently attached to the car like many I've seen on the site), but the bike rack is sturdy enough that I should be able to build something big enough to make a really decent gain. I'm actually thinking if I can get a really big piece of sturdy, but flexible, clear plastic, I can make it cone-shaped, and I won't have to move taillights or worry about installing a window. I've yet to look into that in any way, but if anyone has thoughts, I'd love to hear them.
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Old 07-08-2010, 05:55 PM   #10 (permalink)
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Drums, be careful with the grill blocking on an MCS. Your engine is supercharged, and the area you are blocking not only houses the radiator, but allows some additional air to make its way to the intercooler (which is primarily fed by the hood scoop). Your climate in Portland in your best ally in keeping your engine cooled with a blocked radiator, but that engine tends to run warm, so keep an eagle eye on your coolant temps. Good luck with the mods, can't wait to see more pics!

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