By Staff Writer
Apr 8, 2009 | Mini | Posted in Shop Work | From the Aug. 2006 issue | Never miss an article

Story By Per Schroeder

The entry-level MINI Cooper has a lot going for it. You don’t need to go for the more expensive supercharged Cooper S to get a car that handles amazingly well, gets great gas mileage, and has a healthy aftermarket. In fact, we think the base Cooper is closer to the concept of the original Mini, since it uses its small size and light weight instead of raw power for giant-killing performance.

The basic MINI has been a favorite of ours since we built up a 2002 model as a project car a few years ago. Now we’re working on our second one, a 2005 model that our technical editor is autocrossing nationally. Using this car as an example, we outlined quite a few tricks and tips in the April issue of GRM to get the Cooper and Cooper S to handle even better. Now it’s time to upgrade the straight-line performance of the Cooper—without breaking the bank.

Since we’re running our MINI in SCCA H Stock autocross competition, we’ll be sticking with just those modifications that are legal under the class rules. Those allowed modifications include fluid changes, a different air filter element, and an aftermarket exhaust system after the catalytic converter. While these changes may appear mild, they are a good starting point for any range of modifications—whether the end use is street, track, autocross or whatever. Here’s what we found:

Baseline Testing

zero-to-60 mph: 8.5 seconds
horsepower: 106.1
torque: 102.3 lb.-ft.

The MINI Cooper isn’t the quickest car on the lot, but it accelerates very strongly in first and second gears—especially when you consider that it only has 1.6 liters of displacement.

The 2005 and 2006 cars have a new Getrag gearbox that has slightly tighter gear spacing than the 2002-’04 models, meaning that our later car requires a shift to third gear for the zero-to-60 mph sprint. Our average time for five starts was 8.5 seconds, which is slightly quicker than the factory spec of 8.7 seconds. Credit the cool, 60-degree Florida winter day or our extra-grippy asphalt for the two-tenths difference.

Once we had recorded baseline acceleration numbers, we drove to nearby Holly Hill, Fla., and strapped our MINI to the rollers at Projekt 7 Tuning for some baseline chassis dynamometer figures. The Cooper is rated at 116 horsepower at the crank from the factory, so once you figure in driveline losses, our starting figure of 106 horsepower at the wheels is within the normal range for a Cooper. This is actually very close to the baseline numbers that our 2002 model put to the ground when we tested it on another Dynojet chassis dynamometer.

Red Line Oil PowerPack

price: $85.95
horsepower: 107.7
torque: 103.9 lb.-ft

Red Line Oil recently started packaging its synthetic lubricants into combination packs that are easy to purchase and use. The PowerPack for the MINI Cooper (it also works on the Cooper S) includes five quarts of their 5W30 synthetic oil, two quarts of MTL synthetic transmission fluid, a bottle of WaterWetter cooling system additive and a bottle of SI-1 Complete Fuel System Cleaner. It also comes with a Red Line Oil embroidered hat and a collection of stickers. While this convenient package was created to market Red Line products to new customers, it does make it easy to completely switch a car to Red Line products in one fell swoop.

We were approaching 10,000 miles and our Cooper was due for its second oil change, so we drained out the factory-recommended Castrol 5W30 synthetic oil and poured in the four-plus quarts of Red Line’s finest. The transmission was also drained, and we then used a small hand pump to squirt in the two quarts of MTL. Next up, the WaterWetter was poured into our coolant expansion tank (we used a turkey baster to remove some coolant first so we wouldn’t have any overflow problems). The SI-1 was poured into a full tank of premium unleaded fuel.

The MINI was started and allowed to warm up on the dyno’s rollers. We covered about 30 miles on the rollers, going up and down through the gears to thoroughly mix in the new fluids. Once that was done, we sampled our horsepower and torque, coming in with an additional 1.6 horsepower and 1.6 lb.-ft. of torque. While that slight gain may lie within the margin of error of most dynos, it was repeatable and we’ve found in the past that the Red Line products offered noticeable improvements in shifting and engine performance.

ITG air filter

price: $65
horsepower: 108.26
torque: 103.86 lb.-ft.

Now it was time to test a different air filter. We used a small Torx bit to open up our air filter assembly so we could remove the stock paper element. We replaced it with an ITG foam air filter that we purchased from MyMini of Pompano, Fla.

The ITG air filter is made with three layers of foam, each with a different pore size. The filter is coated with a light oil to attract microscopic dust as air passes through.

With the car buttoned back up, we reran the dyno test. This time, we saw only a small improvement, just half a horsepower with no gain in torque. These numbers are probably within the realm of statistical noise, so we’ll chalk the filter up to one of those modifications that didn’t hurt and will make our lives easier, as we can just clean and re-oil the filter when it gets dirty.

Borla exhaust

weight: 25 pounds
price: $550
horsepower: 110.2
torque: 106.4 lb.-ft.

Next we crawled under the car and unbolted the factory exhaust system. The 31-pound factory system is nicely built with smooth mandrel bends, 2-inch stainless tubing and a rather attractive, subtle exhaust tip.

The Borla system, in comparison, is made out of 2.25-inch stainless steel tubing with a large resonator and rear muffler. The system wraps up with a 4.5-inch polished tip. While beefier than the stock system, the Borla setup tipped our scales at 25 pounds, about six less than the factory part. Weight loss is one of the more important improvements that a racer will make in stock class autocrossing.

All of the required clamps and hangers were ready to go, so installation of the Borla exhaust went pretty easily. The Borla system is constructed in three pieces, instead of the factory’s one, so it does take some adjustment of each piece to get the tip centered in the rear valance.

We started up the car and were greeted by a throaty rumble from the exhaust as we accelerated through the gears. To get the car’s computer acclimated to its new exhaust system, Jerry Baggett, Projekt 7’s dyno operator, ran the car on the rollers for close to 45 minutes, with several start and stop cycles to allow time for the computer to get its bearings. At the end of this session, we shut the car off and allowed it to cool back down while we grabbed lunch.

After some tasty Krystals, we started the MINI back up and allowed it to return to operating temperature. This time, the MINI rumbled its way up to 110.2 horsepower and 106.4 lb.-ft. of torque. That’s about 2 horsepower and 2.5 lb.-ft. of torque more than we made with the stock exhaust.

While well built, the Borla system was a bit on the loud side for our tastes. It droned quite a bit in the mid-range, and we decided it was better suited to those interested in a more noticeable exhaust note.

MagnaFlow exhaust

weight: 24 pounds
price: $580
horsepower: 110.1
torque: 106.1 lb.-ft.

The MagnaFlow exhaust system has proved to be very popular among autocrossers. At 7 pounds lighter than stock, it’s one of the lighter aftermarket systems available; it also reputedly produces some of the better horsepower figures.

Like the Borla, the MagnaFlow exhaust system is crafted out of polished 2.25-inch stainless tubing and features both a resonator and a rear muffler. In this case, the rear muffler is more of a bullet-style with a large 5-inch exhaust tip. It’s a little racy (ricey?) for our tastes, but it came with a lot of recommendations.

Constructed out of just two pieces, the MagnaFlow system was one of the quickest installs. We snugged it down and started the car back up for its next pulls.

The MagnaFlow was clearly the loudest exhaust system of the bunch. Not only did it have the mid-range drone that plagues many aftermarket MINI exhausts, it also had a very raspy bark at anything more than half-throttle. Much like racing Minis of the 1960s, the MagnaFlow-equipped MINI sounds a lot like a swarm of killer bees on the rampage. Music to some….

As for horsepower, the MagnaFlow posted very similar numbers to the Borla, producing 110.1 horsepower and 106.11 lb.-ft. of torque.

MyMini exhaust

weight: 21 pounds
price: $399
horsepower: 110.2
torque: 106.9 lb.-ft.

When compared to the other systems we sampled, the MyMini exhaust system for the MINI Cooper is unique: It is available in several different configurations, and it’s made with the smallest diameter tubing (just 2 inches across). You can purchase it as a Sports system or a Touring system, and each can be purchased with or without the center resonator. The Sports model is aimed at racers who are more interested in power and weight, while the Touring system is geared toward those enthusiasts who want a more subdued tone.

We tested a Sports system without the resonator. This was the lightest system that MyMini offers; at 21 pounds, it weighed 10 pounds less than the stock setup. Surprisingly, the MyMini Sports exhaust system was also one of the quieter exhaust systems of the bunch, with just a burble at idle and a bit more thrum under acceleration. The Sports version does have some drone while cruising under throttle, but it’s noticeably less than the Borla or Magnaflow. If you like even less noise, you can choose one of MyMini’s quieter versions.

The MyMini Sports system produced our highest performance numbers of the day, 110.23 horsepower and 106.9 lb.-ft. of torque. The smaller-diameter tubing was obviously not a detriment to performance on the MINI’s 1.6-liter engine, and may even have helped the peak torque somewhat.

At the end of our first day of testing, we had gained more than 4 horsepower and about 41/2 lb.-ft. of torque. That’s a healthy improvement on an already well-optimized car that competes in a very restrictive racing class.

We drove around for about a week with the MyMini exhaust and competed in an autocross with it, noting the improved mid-range that helped our MINI pull out of corners with more authority while the improved top end helped our speed at the end of each straight. Performance-wise, there was no downside to our first modifications. Looking back at the dyno charts, we can see that the performance exhaust added close to 5 horsepower and 6 lb.-ft. of torque at 4000 rpm, right where we were noticing our gains.

Milltek exhaust

zero-to-60 mph: 8.0 seconds
weight: 25 pounds
price: $540
horsepower: 108.2*
torque: 105.0 lb.-ft.*
*note: revised baseline

The Milltek Sport exhaust system is widely regarded as the system to get if you want an improvement in power without any real increase in noise levels. Like the other systems, it’s a quality piece constructed out of stainless steel and features a resonator and polished rear muffler. A subtle 4-inch exhaust tip is used to attract little attention.

About a week after we had concluded our initial exhaust testing, a Milltek Sport exhaust system for the Cooper arrived from Webb Motorsports. Through no fault of theirs, the Milltek for the Cooper S had been shipped first, so we had to wait an extra week for the correct one to arrive. This meant that it missed our first round of testing and we’d have to schedule another session in the dyno shop.

We drove back down to Projekt 7 Tuning for another crack at the Dynojet rollers. While we had originally planned to get all of the systems tested in one day, the Milltek had come so highly recommended that we couldn’t ignore it.

As can sometimes happen with dynamometer testing, once we got the car on the Dynojet we found that our baseline was considerably different from our previous one. With the MyMINI Sports system in place, our car now pulled 106.1 horsepower and 102.3 lb.-ft. of torque; this was approximately 4 percent off our previous readings. While a week had passed, the weather was very similar, with high-60-degree temps and low humidity. Our only guess is that either the car had a bad load of gas or the dynamometer itself was having issues.

We quickly bolted on the Milltek system and retested the MINI. With the newer exhaust in place, the car put out 108.2 horsepower and 105.0 lb.-ft. of torque, with considerable gains in the low- to mid-range areas. The exhaust note with the Milltek system was as quiet as promised, with just a touch of extra rumble here and there. (We appreciate the lack of drone at highway speeds, as that makes our long drives to autocrosses that much more pleasant.)

We retested our zero-to-60 mph standing start acceleration to get a real-world comparison to our baseline, and found that with the Milltek exhaust, ITG air filter and Red Line fluid changes, our car turned consistent 8.0-second times. This was a full half-second quicker than our baseline. Not bad.

Bolt-On Mods for the Cooper S

In addition to prepping several “standard” Coopers, we have also set up the supercharged Cooper S for competition duty. The Cooper S actually responds to bolt-on modifications much better than the normally aspirated Cooper.

Typical intake modifications that do away with the factory airbox are good for about 5 horsepower, while exhaust system changes can yield big numbers depending on how much noise you’re willing to tolerate. A street-friendly exhaust system from Borla, MagnaFlow, Milltek or Supersprint can give the car an additional 10 horsepower pretty easily while not causing deafness.

The next step for many owners is a smaller pulley that spins the blower faster, equating to more boost for the 1.6-liter engine. These are inexpensive (less than $150 from many vendors) and extremely effective. Aftermarket pulleys are usually 15 percent smaller than the stock piece, and can yield about 15 additional horsepower and 10 lb.-ft. of additional torque. We would caution that HPDE and track-day competitors shouldn’t go with a pulley that’s more than 15 percent smaller than stock, as extended levels of high boost can lead to a failed head gasket.

After increasing the boost and performing typical intake and exhaust modifications, your next logical step would be to reflash the ECU to optimize the air/fuel ratio. Larger intercoolers can allow for a more efficient cooling of the intake charge, while aftermarket cams are also available and effective. The end result of these more extensive modifications can top 190 horsepower to the wheels with little real effort. This can make a MINI Cooper S a real scorcher on track.

What Next?

While that wraps up the modifications that we’ll be doing to this Cooper, it’s not the end of possibilities for MINI enthusiasts. Intake systems, reflashed ECUs and headers are all available for the car, while drivers of the Cooper S can take advantage of all of these modifications and start playing around with smaller supercharger pulleys and more efficient intercoolers.

Like the original Mini, almost anything is possible when it comes to modifying these cars.

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