Improving Your MINI Cooper

You’ve probably already been impressed by how good the MINI is at what it does. It’s quick off the mark, fast on the highway, and can zip around corners at an enviable clip with almost no body sway or looseness.

What’s to Improve?

To be more specific, the stock MINI Cooper S can get from zero to 60 in just under seven seconds, which puts it easily in the middle of the pack of what are called “performance cars.” Top speed is north of 130 miles an hour, which also makes the car quite respectable in the sports car league. That speed is much faster than most of us should be driving, even on a closed course, though it does mean that at normal highway speeds the engine is right in the middle of its power band with lots of reserve power when needed.

Cornering is where the car really excels. BMW has a well-deserved reputation for suspension engineering, and it is really reflected in this car. Compared to even the best of the performance cars, this car chews up corners without looking back, leaving most of the rest of the pack at its rear.

However, there are still areas where the MINI’s performance can be improved. That’s not surprising, of course, since the design and development of a modern car is a balancing act. A wide variety of vehicle specifications are affected by laws and regulations. Fuel economy, smog emissions, and crashworthiness requirements all challenge designers by adding weight and putting limits on engine performance.

And all of this regulation-following and customer-pleasing has to be put together into a car at a price that will be competitive in the marketplace and still produce a reasonable profit. So automobile designers and engineers have to make compromises.

The great thing about the MINI is that the basic platform is well-designed and very well put together. So once you’ve decided what kind of a MINI owner you want to be, you can make the changes you want so that your car won’t be just some product planner’s package of compromises. And with some knowledge and care, you can make your changes without having any bad effects on the overall quality and reliability of the car.

So if you will all take your seats, we’ll start the first class in “Maximizing Your MINI 101.” In this first class, we’re going to focus on the principles of making the MINI make more power. We can do that because the steering, handling, and braking are all well above average, so we can save those factors for a later class.

The Basics of Internal Combustion

Let’s start at the beginning. Your MINI is powered by an internal combustion engine. Aside from some electric cars, nearly all cars on the road have IC engines. All this means is that the power is produced by an explosion—combustion— that happens inside—internal to—the engine.

 In contrast, in an electric car the combustion happened somewhere else, at a power plant or in the sun. The resulting energy was sent over the electric power grid to be stored in the car’s battery and then used by the car’s motor to produce power.

With a hybrid car, the power still comes from internal combustion within the car’s engine. However, what makes the car a hybrid is that it also has an electric motor that can be used as both to produce power and to generate power. Normally the car is driven by the IC engine, and any excess power is used to make the electric motor generate electricity, which can be stored and used by itself, or in conjunction with the IC engine. But we digress.

In an internal combustion engine, the power is produced by the interaction of three forces. Air is pulled into the engine, is mixed with gasoline, and then the mixture is compressed by the cylinder and ignited by a spark to produce an explosion which pushes the cylinder down, turning the crank, and producing power. Air, fuel, and spark. Once the explosion occurs, the only remaining task is to get the resulting smoke out of the engine as quickly and efficiently as possible, so a fourth factor, the exhaust, enters the equation.

In modern automobiles, to provide the fine-tuning needed to maintain performance while meeting emission regulations, the air/fuel/spark equation is controlled by an engine control unit (an ECU)—a computer which controls basic engine operations like fuel mixture and spark timing— linked electronically to the throttle pedal and to several sensors that measure engine performance.

The S Stands for Supercharger

In the MINI Cooper S, the engineers added another component, the Mini Cooper Supercharger, which is only used on high-performance cars. It is used on Jaguars and Bentleys, for example, but on few cars as inexpensive as the MINI. The presence of the supercharger is one of the few major differences between the MINI Cooper and the MINI Cooper S

 The supercharger is worth a few words on its own. As we mentioned, in order for the fuel to burn, we need air. If we want more powerful combustion, then we need more air.

This principle first became an issue back in the days when all airplanes used IC engines and the designers wanted their craft to fly higher. However, the higher the airplanes flew, the thinner the air became. With less air, there was less power produced by the engine. So engineers came up with the idea of using a little component with spinning blades, powered off the engine, to compress the air coming into the engine. With more air being forced into the engine, more power could be produced. They called it “supercharging” the engine.

It wasn’t long before automobile designers were using the same invention on the ground to make race engines run faster without having to get bigger. Remember the “Blower Bentleys” that were raced at LeMans in the early 1930s? You probably don’t, unless you’re an auto history buff. They were probably the earliest well-known application of a supercharger in a racing car. But if you want to impress your car buff friends, just tell them you have a “blown” MINI and refer to your supercharger as the “blower.”

It’s that same principle we find in the MINI Cooper S today. A small turbine between the air intake and the engine is driven off the main driveshaft by a pulley and belt to compress air coming into the engine. More air means that more fuel can be added, and more power will be produced.

Incidentally, engines in some other makes of cars address the same problem of compressing the intake air by using turbochargers. The difference between a supercharger and a turbocharger is how the little vanes in the turbine are powered. In a supercharger, the power comes directly off the driveshaft, connected to the supercharger pulley by the main engine belt. In a turbocharger, there are two sets of vanes, connected by a shaft. Exhaust gas coming out of the engine spins one set of vanes, which in turn push the other vanes that push air into the engine.

The problem with a turbocharger is that you’ve got to wait for the engine to build up some exhaust pressure before the turbo kicks in—what the gearheads call “turbo lag”—which means that the added power isn’t immediately available. With a supercharged engine, the supercharger spins faster as the engine gains speed, so the added power is always on tap and ready for use.

A Shopping List of Basic Improvements

One of the great things about the MINI is the robust nature of the basic engine. It is capable of producing much more power than it does right out of the showroom, even with the supercharger. There are some good reasons why it doesn’t.

For one thing, an engine that produces better performance costs more money. Materials used in a high-performance engine are better and the engine is assembled with greater care, both of which add costs.

However, most people really don’t care enough about performance to want to pay the extra price. Also, with higher horsepower, the engine doesn’t produce as many miles per gallon, and is more difficult to tune to meet emission limitations, so the product designers, even in the MINI, simply had to make some compromises.

But you don’t have to compromise. Aftermarket suppliers (the companies that make products that are bought by owners after the car is bought from the dealer) have developed a number of products that will allow you to improve the engine performance in your MINI to get better pick-up, higher speed, and simply more driving satisfaction under all speeds and situations.

If we think about that basic air/fuel/spark/exhaust equation, we want to do four things. We want to increase the amount of air entering the supercharger and we want to increase the compression capability of the supercharger, both to get more air into the combustion chambers. Then, we want to have the ECU take advantage of that added air flow to by altering the fuel mixture and timing for performance efficiency, and we want to make sure that all the smoke from the combustion can get out of the combustion chambers quickly.

We can make those improvements by upgrading the throttle intake and supercharger pulley, reprogramming the ECU,  and upgrading the exhaust system. Since each of these components operates as part of the overall internal combustion cycle, you’ll get the best performance from each if you upgrade them all at once.

However, if you can’t do that, you can upgrade these components in any order that appeals to you and you’ll still notice the improvement that each component contributes to overall engine performance. And when you’re done, you’ll really have an engine you can brag about. We’ll discuss the upgrades in the order that they occur in the operation of the engine and describe the upgrades you should consider.

Mini Cooper Cold Air Intake System

Before we can have combustion, we have to have air. If we can increase the amount of air flowing into the supercharger intake, and keep it as cool as possible, then we’ll be helping the supercharger do its job by giving it more air to breath.

A typical cost for the parts for an upgraded Mini Cooper cold air intake system is about $200. The design is simple, and can be installed by anyone with the instruction sheet and the proper wrenches in a few hours or less. If it is done in a MINI service shop, it shouldn’t take more than half an hour of shop time.

Making the Supercharger More Super

As we discussed, the supercharger works by forcing more air into the engine. It seems logical to assume, then, that the more air you can get it to push, the more horsepower the engine will produce. In fact, this assumption is true.

The supercharger blower is driven by a shaft connected to a pulley which in turn is rotated by a belt that is driven off the engine drive shaft. (This is the same belt that drives the alternator, and the water pump.) Every time the drive shaft makes a complete rotation, the belt around the supercharger pulley is moved a certain distance.

If you remember your basic geometry from high school, the distance around the edge of a circular object like a pulley—the circumference—is determined by the diameter of the pulley. The smaller the diameter of the pulley, then the smaller the circumference of the pulley. With a smaller circumference, less movement of the belt is required to cause the supercharger shaft of the pulley to make a complete rotation.

Or you can think about it another way. If we put a smaller pulley on the supercharger, then the supercharger will spin more times during the same number of revolutions of the engine. And the faster the supercharger spins, the more air is pushed into the engine.

That’s the basis for our next horsepower improvement. By installing a smaller pulley (and the shorter belt that will be required to go with it) we can increase the speed of the supercharger and the amount of air being pushed in. Tuners call this “increasing the boost.” Not surprisingly, since the principles are simple, aftermarket suppliers have developed smaller pulleys that you can substitute.

Of course, there are some limits to how much boost an engine can absorb without blowing itself to pieces, so there are limits to how small a pulley can be used effectively. For this reason, BMW may be reluctant to honor its warranty if you replace its very conservatively designed pulley with one that produces more boost.

 Most reputable suppliers supply pulleys that are small enough to make a difference in horsepower, but aren’t so small that they could blow the engine. As long as the pulley diameter isn’t reduced by more than 15 percent, there should be no problems, If the pulley is replaced by one that has a radius of less than 85 percent of the original, it will spin the supercharger in excess of its maxium rated specification, putting the engine itself at risk. Even if the engine isn’t pushed hard, if the pulley is too small, the belt angle will be so acute that the belt life will be significantly shortened.

Replacing the original pulley on the engine is not a simple job, since several other components have to be removed to get access to the pulley, and a special tool is needed to remove the pulley. Even with the special tool, an experienced mechanic may take several hours to do the job the first time. With a little practice, the job still takes about an hour.

So if you decide to replace your pulley with the smaller one, you should probably find a shop that has experience in replacing MINI pulleys. The replacement pulley and belt will cost about $200 and the installation about two to three hours of shop time.  In terms of horsepower improvement per dollar, this is probably the most cost-efficient change you can make to the engine.

RACING REGULATIONS AND ENGINE UPGRADES

There are several motorsports sanctioning bodies in North America that run competitive track and autocross events in which MINIs can compete. However, each of these groups has its own rules that specify the class in which a car may be run, depending on the modifications that have been made to the car.

Similarly, the BMW Car Club of America organizes competitive track racing events for BMW-manufactured cars, including the MINIs. For MINIs that will be run in “Spec” classes, some modifications and upgrades are permitted—some are even mandatory—but other upgrades are not allowed under the rules.

If you are now planning to enter your car in these competitions, or even considering the possibility, you should definitely read the last section of this book, and you should obtain a copy of the modification rules that apply to MINIs to make sure that the changes you make to your car will be legal in the group with which you want to run.

Of course, all of the modifications suggested in this chapter can be reversed if they violate the rules of the sanctioning group you want to join, should you make the modifications suggested in this chapter and then decide later that you want to go racing. But if you know now that you intend to race your MINI with a specific sanctioning body, check the rules to save yourself unnecessary time and expense later.

Electronic Throttles, ECUs, and Fuel

Until very recently, the amount of fuel that went into an IC engine was controlled by a needle valve in a carburetor, which was connected directly to the gas pedal. You pushed the gas pedal down, the needle valve would open, and gasoline would be mixed with the air being sucked into the engine. The further down you pushed the gas pedal, the more gasoline that would go into the engine, and the faster the engine would go.

With the engine speeding up, there was less time for the fuel to explode in the cylinders, so the spark had to occur earlier in the cycle to give the explosion time to really work effectively. This factor is called ignition timing. In most engines, a system of weights and springs inside the distributor would compensate for engine speed, changing the timing of the spark.

The process was all very mechanical. And you were the only brain involved in the system.

Nowadays, it is a wee bit more complicated. First of all, no one uses carburetors any more on street cars. Instead, fuel is added to the air going into the engine with a fuel injection system. A fuel injection system has fewer parts, and therefore is less expensive to make and easier to service, so carburetors have gone the way of crank starters.

A second difference is that, to help meet those increasingly stringent environmental and mileage regulations, engineers have installed a little computer, that ECU we mentioned. The Mini Cooper ECU is connected to your throttle with an electronic connection, so your throttle is more like a big dimmer switch than the lever it used to be. Auto engineers call this a “throttle-by-wire” system.

The ECU tells the Mini Cooper fuel injectors how much gasoline to add to the air flowing into the system and tells the spark plugs when to fire during each engine cycle, changing the amount of gas and spark timing, depending on a variety of factors. This little computer bases its calculations not only on how much you push the throttle pedal, but also on the speed of the engine, the amount of unburnt fuel coming through the Mini Cooper exhaust system and other factors.

Think of it as a little brain that not only breaks your decision—“I want to go faster”—into many smaller decisions about fuel and timing, but also decides sometimes that you really wouldn’t have asked for so much speed so quickly if you knew how much gasoline you were using, and how much exhaust you were pushing into the atmosphere.

In other words, the ECU modifies your decisions in order to help the engine achieve maximum gas mileage and comfortably meet 50-state emission restrictions.

However, within a reasonable range, you would probably want to overrule the computer if you could, or at least modify its decision rules. But for that, you would have to be not only an automotive engineer, but also a computer programmer, wouldn’t you?

Not really. The nice thing is that some good automotive engineers and computer programmers have designed a little computer that you can use to tell your MINI’s ECU to modify some of its decision rules in order to give you better performance. This process is called “remapping” the ECU.

These ECU reprogrammer computers modify the software in your car’s ECU to change the ignition timing and fuel relationships at different engine speeds to improve performance. They also change some other factors, such as rev limits, acceleration enrichment, and fuel mixture so that the engine will be more responsive when you push or release the throttle pedal.

One example of these little gadgets is the “Shark Injector ECU Upgrade”  designed and programmed for use on the MINI Cooper S. The Shark Injector is designed to change the program in your car’s ECU to optimize fuel mixture and ignition timing across the entire engine RPM range, but has been programmed to provide a safe margin in order not to risk any damage to your engine.

The Shark Injector is available in two versions, one to upgrade for use of 93 octane gasoline, and one for 91 octane gasoline. The one you use will depend on the quality of gasoline available in your area.

Technically, this is probably the easiest performance upgrade you can make to your MINI. ECU upgrades typically cost around $400. Since you do the change yourself, there isn’t any installation cost.

Performance Spark Plugs

To take full advantage of the enhanced performance that can be gained by upgrading the air intake system and remapping the engine control unit computer, you’ll also probably want to upgrade your Mini Cooper spark plugs. An expanded and more consistent spark flame will provide more sustained and consistent explosions within the cylinders. This in turn will give you smoother engine operation and more consistent power across the engine revolution range.

One spark plug that we can recommend from our own experience is the NGK Iridium IX, which features a 0.6mm iridium center electrode. The high-tech material improves ignition within the cylinders without sacrificing durability. The tapered ground electrode increases the expansion of the flame center as the spark plug fires, and the superior heat range afforded by the plug design is well-suited to high-performance driving. These spark plugs retail for about $8.00, adding less than $32 to the cost of your upgrades. That’s a small but sensible investment in engine performance on both the Cooper and Cooper S.

Mini Cooper Exhaust Improvements

Of course, the air and fuel going into the engine, and the spark that ignites it are only the beginning and middle of the process. Horsepower and torque are also affected by how easy it is to get the smoke out of the engine that is left over after the gas and air explode. After the piston has been pushed down by the explosion in the cylinder, as it comes back up it pushes the smoke from the explosion out the exhaust valve and into the exhaust system. If the smoke can’t get out easily, that puts pressure on the piston, making the engine work harder.

As a result, performance improvements also can be made by improving the exhaust system. In the MINI, the exhaust system consists of “headers”—those pipes into which the exhaust gas flows after it comes out of the “head”—the top part of the engine. From the header pipes, the exhaust gas flows into a catalytic converter (sometimes called a “cat”), which is the essential element of the modern emission control system that captures contaminants rather than letting them flow out of the tail pipe.

The exhaust gas flowing out of the cat is piped through the muffler to reduce noise, and from there out the tail pipes. The muffler, and the pipes into it and out of it to the tailpipe are often referred to as the “cat-back” part of the exhaust system.

If we can make the exhaust gas flow more easily, we will increase the power that the engine can produce. This can be done by replacing the factory-designed system— which was engineered to a budget and designed to reduce exhaust noise as much as possible—with a more efficient Mini cooper cat-back exhaust system.

A variety of different types of cat-back systems are available for the MINI. The differences among them are cost, installation convenience, performance, and—very important to many drivers—the exhaust tone. Exhaust systems, like the curry in your favorite Indian restaurant, can be ordered in mild, medium, or aggressive form.

Three different systems are good examples of these differences. The least expensive we’ve found, at about $700, is a two-piece system designed by MiniMania with a single muffler and large-diameter tailpipe outlet.

Though this system uses factory-mounted installation points, it uses a different design than the original, incorporating two sequential mufflers, making it easy to install and weighing approximately 20 pounds less. The system produces increased performance, and has a nice medium-aggressive sound.

Borla, the well-known exhaust company, makes two different cat-back exhaust upgrades for the MINI. Both have a different and slightly more complex design that incorporates two separate mufflers exiting through twin tail-pipe tips at the rear, similar to the original system. The basic system offers good performance improvement, while maintaining a factory-like tone, while the “Sport” cat-back offers slightly better performance and incorporates different mufflers to produce a much more aggressive tone. Both are priced at about $800.

These Mini Cooper cat-back exhaust systems aren’t difficult to install for anyone with a good set of wrenches and a little garage experience. However, if you don’t fancy putting your MINI up on jack stands and crawling under it to make the changes, a good muffler shop can make the substitution in about an hour or two of shop time.

The Total Engine Upgrade System

Those are the four areas—Mini Cooper air intake, supercharger boost, the ECU-controlled fuel mixture and ignition timing, and the cat-back exhaust—where the performance from your MINI engine can be upgraded easily to go from very nice to wow, while still being street-legal. If you don’t want to go the whole improvement route all at once, you could install these four upgrades in any order you prefer, and with each upgrade you’ll notice performance improvements that will make your street driving and touring more fun and exciting.

However, since the components all work together, it would be nice to do them all at once. The total cost of the parts and installation should come to around $2000. The total system, based on performance tests, will significantly improve mid-range driving pleasure and increase peak performance to approximately 215 horsepower.

By comparison, the MINI dealer-installed John Cooper Works option brings performance to 210 horsepower and will cost about $6000 installed.

Of course, installation of the JCW option won’t affect your factory warranty, which is a good thing. On the other hand, the aftermarket equipment from some suppliers is good enough that they are confident it won’t affect the performance of your engine, so they are willing to offer their own warranty on the installed components.

With these aftermarket warranties, if something goes wrong with the engine after you install the components while the engine is still under warranty and the dealer won’t pay to repair it, their warranty may very well pay the costs of the repairs. (You’ll want to ask your supplier about the details of their warranty, of course, and read the fine print, but at least you know that you have an alternative to the dealer-installed performance upgrades.)

Street and Touring Engine Upgrades for the Cooper S

(Approximate costs including installation)

Improving the Handling

Having fun with a car isn’t just a matter of how quickly it accelerates or how fast it will go in a straight line. Really enjoying the driving is also a matter of how easily the car can be driven around corners and how stable it is at speed. We’ve been very impressed with those aspects of the MINI since it was first introduced. We certainly wouldn’t argue if you decide to wait until you’ve gotten some miles on the car and maybe had a chance to really push the car around a race track or autocross course before making any suspension changes.

However, if you’re looking at the car now and thinking you’d like to make some changes in its appearance to give it a more custom appearance, or if you’d like to make a few improvements in its handling right now, we suggest the first thing you consider is replacing those tires and wheels that came with it.

When we were giving suggestions on buying the car, we recommended that you not spend the money on bigger wheels or fancy tires, so if you did take our advice and took delivery of your Cooper S with the standard 16-inch wheels, and didn’t opt for the sport package, you’ve got at least $800 in your piggy bank to buy new tires and wheels.

If you bought the Cooper model before reading this book, changing the wheels and tires is one fast way to give the car a similar appearance to the Cooper S. Going to 17-inch wheel from the original 15-inchers will make a major change in the look of the car, immediately giving it that “performance” style.

If you’re ready to do it now, look at the wheel and tire suppliers, like Tire Rack or the MINI-specific suppliers and pick some sharp 17-inch wheels. Just remember that you want light wheels, so check those specifications. Look for a wheel that weighs 22 pounds or less, to get the greatest improvements in handling.

The same weight consideration applies to the tires. Those run-flats that came with the car may make you feel a little safer since you won’t have to worry about changing a flat tire on the interstate, but they just weigh too  much for good performance, and they aren’t as responsive as regular radial tires. They also give a rougher ride than regular tires, even the low-profile high-performance tires that you’re likely to buy.

Most owners upgrading their wheels are likely to prefer 17-inch wheels, mounted with low-profile tires, because the larger wheels offer more stability, ride more smoothly, and will put more rubber on the road. The larger wheels also are more likely to have the space to fit larger high-performance brakes should you decide to do that later. The low-profile tires also give less squirm in the corners, one of the factors that contributes to that “razor-sharp” handling the car magazines often go on about.

The specific brand of tires is largely a matter of personal preference. Kumho, Yokohama, and Bridgestone and other manufacturers all make tires with good performance reputations. Talk to other MINI owners about theirs and we’re sure you’ll get some good suggestions.  MiniMania mounts their wheels with Kumho Ecstas, a good all-around choice for street, autocross, and track use.

As an example of cost, a good set of wheels and tires for your MINI can be purchased for less than $1500. Of course, if you want to get into fancier wheels, the sky’s the limit, though much past $1500 you’ll be paying for looks more than performance.

As far as the risk of flat tires is concerned, modern tires actually have very few flats under any circumstances, so you don’t really have to worry about not having run-flat tires. Nevertheless, several accessory suppliers make a kit that will fill the hole in the flat tire and an air compressor that will plug into your car’s power outlet to inflate the tire. It certainly is a good idea to have one of those kits in the back. But we’ll bet that you’ll be much more likely to use the inflator to fill up your beach ball or air mattress than ever fill up a flat tire.

Other Upgrades for Your MINI

There are a number of other upgrades that might be appropriate right now to improve your MINI’s performance on the street. Some of these for you to consider include the following.

•  Mini Cooper Short shifter kit. Reduces shift lever movement required to change gears, which improves shifting performance and provides more satisfying shift action.

•  Improved Mini Cooper  brake pads. Better brake pads, such as Greenstuff pads, will reduce brake dust, decrease brake pad heat, and provide more brake bite.

•  Spark enhancement systems. Various products, such as the Plasma Booster, can improve spark to provide more efficient combustion, increasing horsepower and smoothing out acceleration.

•  High-performance Mini Cooper street clutch. Provides quicker and more positive clutch take-up, using steel-backed organic clutch disc, high-clamp pressure plate, and modified throw-out bearing. Reduces transition time when shifting gears, increasing acceleration.

We’ll review these additional enhancements in more detail in the next chapter when we discuss upgrades that are appropriate for drivers who occasionally use their cars on the autocross course or on the race track at club track days.

Right now, we’ll suggest that you wait until you’ve had the chance to take a driving course and have had the experience of driving on a closed course, before you think about changing brakes, shifter, or clutch. You may be quite happy with the car’s performance right now, and decide that you don’t need all the thrills that high speed and competition can provide.

However, if you find that you enjoy the time you spend on the track, want to hone your skills further, and are already finding that your clutch, brakes, and shifting aren’t quite what you want, then you can seriously consider these additional upgrades. 

Go to Advanced Street Driving Skills