What’s the Diff? Jun 8, 2010
One-wheel drive is a bummer, and a surprising number of cars are, essentially, one-wheel drive. As long as you're not breaking traction it's not a problem. However, in a higher-horsepower front-wheel-drive car that's constantly shifting its weight around a race track, an open differential is unforgivably bad. Our 2005 MINI Cooper S, though armed with a suite of John Cooper Works performance upgrades and MINI Challenge racing goodies in as-delivered form, was hampered by its mechanically open differential.
As a result, powering the car out of tight corners was an exercise in throttle restraint. It was far too easy to get the supercharged MINI to light up the inside tire, and the car was slower than it should have been coming out of corners. MINI did offer a limited-slip differential as an option on Cooper S cars, but this stock unit, while better than nothing, leaves something on the table in a full-race situation on very sticky tires.
OS Giken had our solution. Their Super Lock line of clutch-type limited-slip differentials uses many small clutch plates to ensure smooth power distribution to both drive wheels in a slip condition--up to 100 percent lock. And because it's a clutch design, the differential works even if one of the wheels is off the ground, unlike a standard Torsen design that becomes an open differential if one tire loses contact with the pavement. The Japanese manufacturer has expanded their lineup from brands like Toyota, Nissan and Honda to other popular track brands, including Porsche, the Chevy Corvette, BMW and, by extension, MINI.
Their Super Lock LSD for the MINI Cooper is not an inexpensive upgrade; prices from retailers are typically around $1700. However, the build quality is truly first rate. It's almost a shame to have to seal this thing away from the world inside the transaxle case. The reviews we've heard from racers using OS Giken Super Lock diffs have all been glowing, and a similar OS Giken diff won our differential comparo in a Honda S2000 in our February 2009 issue. Better still, our friend Ian Stewart won the NASA Performance Touring C championships in 2009 in a similar MINI Cooper S equipped with this exact differential.
Since we were going to have to take the transmission apart anyway, we decided to go whole hog and upgrade the clutch at flywheel using OS Giken components. Again, this is a higher-end kit and the price reflects this: another $1700 or so for the combined single-plate clutch, lighter flywheel and pressure plate assembly. Since our MINI Cooper S still has a reasonable amount of inherent value as a newer-model car, we don't feel these upgrades are out of line from a budget standpoint.
The tight packaging in the nose of the MINI means that transmission work can require a pretty comprehensive removal of components. In fact, the easiest way to do the job is to remove the entire nose of the car and pull the engine out completely. NASA TTC champion Ian Stewart's MINI and Volvo shop, Maitland Importers, is just down the road from us in Orlando, Florida. Considering the shop's MINI racing and maintenance expertise, we loaded our MINI on the trailer and headed west for Orlando. With time constraints this was a wise decision, as master technician Philip Cavagnaro had our MINI's block on the ground in about an hour.
Since we had the whole shebang apart anyway, we took the opportunity to install, refresh and upgrade our entire suite of bushings and mounts with Powerflex components. From engine mount inserts to suspension bushings, this is the kind of job you'd regret not doing while everything was apart. It's so much easier with the engine on the ground and a car on the lift. The Powerflex website has a great graphical breakdown of all the possible bushings for any given application, along with the prices. Expect to spend between $25 and $50 each for various sets and pairs depending on your needs.
In our winter downtime, we also installed Ugli Gripz on our Sparco steering wheel. Ugli Gripz is a do-it-yourself kit that allows you to put custom moldable grips on any steering wheel. First you apply silicone tape over the wheel to protect the stock material. Then you apply the grip material and mold it to the shape of your hands. Finally you apply a surface coating, which needs about two days to dry completely. The result is a rubbery, grippy feel that's about as firm as high-density foam. Naturally, the overall diameter of the wheel grip is increased with the addition of material, so this is a great option for somebody looking to thicken up a wheel.
Traction in Action Jul 20, 2010
With our new OS Giken limited-slip differential, clutch and flywheel in place, it was time to do some real-world testing. Our friends at the NASA Southeast region had a full race weekend slated at Roebling Road Raceway, one of the closer tracks to our Holly Hill, Florida, headquarters. With about 10 days left before the event, we decided to attend. That gave us only one weekend to go over the car and ensure everything was in good order--and it's a good thing we did.
Our first step in checking things over usually involves putting the car up on jackstands and removing the wheels. Our first snag ended up being a pretty serious one: the left-front wheel had a frozen lug, and no amount of convincing seemed to loosen the assembly.
The lug was fused to the stud securely enough that applying massive torque only spun the stud. We figured at first that we'd simply unscrew the stud from the hub, as we've done on many other BMW products, but the stud refused to come free. We attacked it with a huge lever, impact tools, a drill, a Dremel--the whole arsenal. All we got was a free-wheeling stud that wouldn't come out and a properly stuck wheel.
We hypothesized--correctly, it turns out--that the stud had some kind of flange or spacer that was keeping it trapped behind the massive rotor hat of our AP brakes. Rather than continue hammering away and ending up with an car unable to even roll back on the trailer, we cut our losses, admitted defeat and put the wheel back on the three good remaining studs.
We were sure that we'd done some serious damage to the hub, so we loaded the car back onto the trailer and did not pass go as we went directly to Ian Stewart's Maitland Importers shop in Orlando. With just a few days to prep the car, we didn't have time to guess at a solution. Ian's shop would have a replacement hub in stock and the know-how to fix the problem in a hurry.
Sure enough, they found that we'd stripped the threads on the hub completely in the affected stud mounting hole. The flanges on the studs that were preventing us from pulling the stud out past the hat were revealed as well.
We needed some extra-long, race-worthy studs in a hurry, so we called our friends at BimmerWorld. Since our MINI has but four studs on each hub, and we're planning on moving up to an even wider tire in the near future, we figured quality and strength were of the utmost importance. Owner James Clay told us that their Premium Race Bulletnose Wheel Stud is the same part they use on their Grand-Am Continental Tire Challenge BMW race cars, and at $9.99 a piece, they're not terribly expensive. We ordered a set of eight to take care of both front hubs. The studs are shot peened and double magnaflux inspected, and the bulletnose design makes starting the lugs on the threads a breeze. They've even got pre-applied threadlocker on the hub threads. We opted for the 92mm variant, but an 82mm option is available.
We lucked out with our timing, too, as Ian's MINI computer guru, Jan Brueggermann of Revolution Mini in California, happened to be at the shop. He couldn't resist plugging his laptop into our MINI, and he found that our JCW ECU flash was a much older version that was causing the car to run rich just about everywhere. He gave us the latest factory JCW flash and found that it leaned things out considerably; he said he wouldn't be surprised if it were worth 15 or 20 horsepower.
Ian had the car ready with a day to spare, so we loaded up and headed to Roebling Road. The race weekend went without any major incidents, and the improved out-of-corner traction that our OS Giken differential was striving to provide was impressive. We say "striving to provide" because our old BFGoodrich R1 tires seemed to be at the end of their lifespan. The MINI was particularly twitchy on the back end, so we lowered our running pressures from about 39 psi to 35 psi in the rear, which seemed to help matters. (We kept the fronts at around 39 psi). We were uncontested in Performance Touring C, so we even came away from our weekend with a shiny trophy.
Our tires are toast, so it's time to make the switch to a set of brand-new BFGoodrich R1s before our next race. We've also got a Sneed Speed Shop front splitter to see if we can't get more grip on the nose of our front-wheel-drive beast. Look for another update from our HyperFest weekend soon, or check out a bit of a video teaser here:
The Fast Airbender Oct 19, 2010
Aerodynamics is a mysterious art, and it's not surprising that many racers shy away from that which they don't understand. Our MINI Cooper S came equipped with a cool JCW adjustable rear wing, but the front end was unaltered. A bit of rear downforce at speed can be a nice confidence builder, but what a front-wheel-drive car really craves is front-wheel grip.
At last year's Redline Time Attack, we met a friendly fellow MINI racer by the name of Chris Sneed. Chris is the head honcho at Sneed's Speed Shop in North Carolina. Chris had recently returned from some wind tunnel testing on his own car, where he'd been playing around with splitter designs in anticipation of releasing his own product. Chris swore up and down that a front splitter was a revelation on these cars, adding palpable levels of grip to the nose and simultaneously reducing drag. He sold us on the concept, and we were delighted when a Sneed's Speed Shop splitter arrived at our office. The kit runs $500 and includes all the necessary mounting hardware plus a really nicely machined thick plastic splitter element. It weighs less than 25 pounds all told.
Our buddy Matt Smith, a car fanatic and engineering student at Embry Riddle Aeronautical University in Daytona, dropped by to lend a hand with the installation. The job required a few specialty items, notably a stepped drill bit for making large holes in the back of the aluminum bumper to allow a socket access to the front element. Nylock nuts hold the majority of pieces in place, and the splitter element is predrilled to attach to existing bolts on the MINI's underside, evening the load. On the leading edge, four adjustable aluminum stanchions and two wind-blocking endplates for the fenders require a bit of drilling, but nothing scary. The MINI's bumper cover is easy to remove, as is the aluminum impact structure underneath.
Our first step was to tentatively locate the splitter using the predrilled holes; this gave us an idea of its final location. Then, we mocked up the stanchion locations and drilled small pilot holes through the bumper to mark the aluminum underneath for the stanchion mounting studs. With our measurements double-checked, we removed the bumper cover and structure and mounted the four threaded studs into the aluminum bumper. We drilled the plastic bumper holes to accommodate the newly installed studs, then confirmed that reassembly was possible. On a second mock-up attempt, we realized that our MINI's stock plastic leading edge was bending the splitter down too far, so we took a Dremel to the bumper plastic to promote a more horizontal splitter position.
When we bolted everything in place for the last time, we were very impressed with the quality and robust mounting of the Sneed's Speed splitter. It's secure, and the threaded stanchions allow easy adjustability of the leading edge angle. A locking nut holds everything in place once the angle is set.
We must have mounted our two outermost stanchions a bit too high, as there were only a couple of threads of engagement available for a high angle. A trip to Lowe's for some threaded steel bar provided a cheap solution and a longer, happier stanchion angle. Alternately, we could have been more aggressive with the Dremel on our front fascia's lower edge, but we didn't want to cut into the shape of the nose too dramatically. With the slightly longer threaded rods in place, we've got solid engagement and a good range of adjustability.
To minimize stress on the piece, it's important to detach the stanchions whenever we load or unload the car from our TrailerWorld trailer. With the stanchions disconnected, the Sneed's Speed splitter has adequate flex for loading and offloading; it bends up a couple of inches as the splitter glides along the aluminum ramps, and there's no drama. Since the install, we've loaded and unloaded a dozen times with no issues.
Before our first race with the splitter on the car, we also removed our worn-out 225/45ZR17 BFGoodrich R1 tires for a set of fresh 235/40ZR17 R1s. Though the listed width differential is just 10mm, the new rubber seemed a bit wider than that in a side-by-side comparison. (Keep in mind, however, that the 235s were unmounted at the time.) Our favorite local tire mounting shop, Orlando & Sons, did the tire busting.
Armed with extra mechanical grip and our new Sneed's Speed splitter, we hit the track at HyperFest. The increase in grip was undeniable, both from a purely mechanical standpoint and in higher-speed corners. We were honestly astonished at how much grip the car had on its nose at higher speeds; it was simply glued to the track, and it begged us to go faster. Our times dropped throughout the weekend, culminating in a 1:27.880 fast lap and a Performance Touring C class win in Sunday's race. We ran toward the front of the Stinger group for nearly the entire session and came out of the car with a huge grin.
Here's a video recap of the weekend:
Velocity in Virginia Nov 12, 2010
Our MINI Cooper S worked really well at Hyperfest, but we ended that event with some additions to our to-do list. The wider tires in the rear were rubbing against the lower control arms, so we needed to address the spacing. Our brakes were just about toast. And we had bloodied the car's nose in an attempt to avoid an accident in Saturday's race. Next on the calendar was one of our favorite events of the year, the NASA Mid-Atlantic Summer Slam following the Ultimate Track Car Challenge at Virginia International Raceway in July.
To remedy our rubbing tire, we found a quick and easy solution at Pep Boys: some 5mm spacers. It's important to have a long enough bolt on the hub when using spacers, but the bolts on the back of our MINI were just long enough for full thread engagement of the nuts. Since the wheel was in maybe 1 to 2mm too much, the 5mm spacers would be plenty to prevent rubbing of the inner edge.
Our MINI Came with some decent brake pads, but after a season of racing they were at the end of their operational life. The car's unconventional setup includes massive John Cooper Racing-branded AP Calipers and discs up front with the stock discs in the rear. Jeff Ritter, the manager of the high-performance division of Essex Parts, was eager for us to try out one of their newest products, the CL RC5+ sintered brake pad. This pad actually has a lower coefficient of friction per unit pressure than CL's angrier pads, but it wears gently. The high metal content means good bite even when cold, and the pad has a very flat friction curve from ambient temperature to over 2000 degrees Fahrenheit. In the rear, Jeff recommended the Ferodo DS2500, another moderate-bite pad with a very even friction coefficient across its operating range, up to about 1300 degrees Fahrenheit.
Compared to the pads that came with our MINI, the CL/Ferodo combination had noticeably reduced initial bit, but that's not necessarily a bad thing. We're used to pads that grab really hard at tip-in once they're warmed up, but at temperature the CL/Ferodo combo liked a firmer foot before reaching threshold. That said, after a few laps we were really starting to dig the increase in pedal feel and modulation sensitivity. Instead of a brick wall of force, the new pads encouraged some nuance under braking, and at the end of the first test session we were really enjoying the setup. The pads were absolutely consistent for both days of racing on an insanely hot weekend, and we didn't even need to bleed the brakes for day two. There was as much bite on the last lap of the 35-minute race at the end of Sunday as there was on the first lap of Saturday's race. We got ours from Essex Parts. Our front part number for our huge AP calipers is 07 5004W50T17.0 RC5+ and the rear part is 11 FCP1676H-N.
The last item on our checklist: taking a closer look at the bumper crack and nose scuff we picked up at HyperFest. The expensive fix would have meant sourcing a new bumper cover, but that seemed excessive considering the minimal extent of the damage. An approximate 6x9-in. decal would be more than enough to cover the wound. We had some old windshield banners lying around our garage, and the end bits were essentially plain white decal material. The white is a good choice, as its high contrast against the dark blue body of the MINI would show up as a simple white square from any distance and any speed on track. Up close you can see a few wrinkles, sure, but the on-track photo shows how the stickers meld into the overall package. We had a couple of die-cut helmet decals in black in the same pile of spares, so we threw them on to further increase the contrast and busy up the section. We mirrored the job on the unscuffed side so it looks more intentional. Plus, it would protect the remaining lens.
From a racing perspective, this was the most fun we'd had in the MINI to date. It's quite well sorted at this point, and the car was dead-nuts reliable all weekend. Thanks to Jeff Williams in a Performance Touring C Toyota Celica, we had a great battle on Saturday. We earned second place after a frantic race-long chase: Watch the video below for details. On Sunday we qualified a rewarding third overall in the Stinger group with a 2:20.249--a new personal record at VIR with the MINI--and drove to a fifth-place overall finish and a win in Performance Touring C.