The Total MINI Cooper 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.)
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Street and Touring Engine Upgrades for the Cooper S
(Approximate costs including installation)
Mini Cooper Cold Air Intake System $250
Mini Cooper Supercharger Pulley and belt $250
Mini Cooper ECU Upgrade $400
Mini Cooper Iridium Spark Plugs $ 32
Mini Cooper Cat-Back Exhaust $850-$1000

Typical Total Cost $1800-$1900
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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.

You MINI Cooper owners can also increase the power on your cars by installing a more efficient cat-back exhaust system. On these kits, a larger primary pipe and low restriction muffler will boost power, and get the bonuses of a little more aggressive exhaust note. At least one attractive system also sports a credibility-building four-inch exhaust tip peeking out under the rear valance. A “silent tip” is included that is easy to install and remove for quiet operation on long trips. These cat-back exhaust kits for the Cooper are available for about $700.

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.

MINI Cooper 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 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.

Reprogramming your ECU is a piece of cake. It’s just about as complicated as upgrading a piece of software on your computer. You plug the Shark Injector into the data port of your MINI and follow some simple procedures to download the remapped program into the ECU.

If for any reason you want to reverse the process and change your ECU programming back to the way it came from the factory, all you need to do is plug the Shark Injector into the data port again and you can swap the original factory program back into your ECU. You can repeat this process as often as you like, since the job takes less than an hour, and it can be done whenever you want.

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.

A similar ECU remapping system designed for your MINI Cooper has been developed by the Evotech company. Used in the same way as the Shark Injector is used on the Cooper S, it is plugged into your Cooper ECU and reprograms it to correct the air-fuel mixture and timing to provide optimum performance at all engine speeds and loads. The price is about $400. The Evotech system has been shown to provide better performance when starting off, improve mid-range throttle response, and increase peak horsepower.

Mini Cooper Racing 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.

One of the most popular such groups is the Sports Car Club of America, which organizes both track and autocross events throughout the country. A similar body exists in Canada. These organizations have several classes that allow cars to run in street-legal condition. Some modifications and upgrades are permitted depending on the class, but what is permitted and not permitted is spelled out in the group’s regulations in order to keep preparation costs to reasonable amounts amd allow drivers to compete against cars with roughly similar levels of modification.

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.

Making the MINI Cooper Supercharger More Super

As we discussed, the MINI Cooper 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.

A Shopping List of Basic Improvements for the MINI Cooper

One of the great things about the MINI Cooper 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.

We can do this by replacing the standard air intake system with an upgraded “Mini Cooper Cold air intake system.” The standard cold air intake system in the MINI is really not all that complicated. Air flowing into the engine compartment through the grille is channeled into an air intake box on the top of the engine. In the box an air filter removes dust and dirt that would create undesirable wear in the engine. From the air intake box, a duct directs the filtered air into the supercharger. In addition to capturing and filtering the air, the ducts on the standard air intake system have been tuned, like you might tune an organ pipe, so that the air flowing through it produces as little noise as possible.

The standard Mini Cooper cold air intake system easily can be swapped for an upgraded one that has been designed with performance in mind. Several aftermarket equipment manufacturers make replacement cold air intake systems for the MINI, but we’ll describe two typical designs.

The simplest way to improve the system is to replace the stock air filter and air intake box with a higher-quality filter that has been designed specifically to increase air flow while still providing the same filtering functions. K&N makes a high quality filter that is used in combination with high-velocity ducts in several of these kits to replace the basic system. Since it can be cleaned and re-used, we don’t have to buy a new filter every time the old one gets dirty.

An alternative approach that not only improves filter performance, but also provides additional air flow into the intake is now being manufactured by several companies. In this system, the entire air intake box and filter is removed and replaced by a conical filter surrounded by an L-shaped divider. This system helps increase power not only by improving filter efficiency, but also by increasing the flow of air into the system.

This system is designed to do a more efficient job of directing the air from the front Mini Cooper grille into the engine’s air intake. In addition, by being open at the top and back, it captures air from the grilles below the windshield, which are in an area of the body where air flow creates high pressure. By ducting some of that air into the supercharger in addition to the air coming in through the grille, the system naturally allows more air to enter the supercharger intake.

To make sure there is as little as possible to obstruct the air flow once it gets into the air box, the cold air intake system incorporates a reusable high-flow cone-shaped air filter. K&N’s popular re-usable high-performance filters are frequently used in this application. The design of the upgraded cold air intake system offers one other advantage. While providing a direct path for air from outside the car to flow into the supercharger, it blocks off the hot air swirling around the engine. As we learned in science class, hot air is thinner than cold air, so the cooler the air going into the supercharger, the more efficiently the supercharger can do its job.

Though generally similar in design, these systems do vary somewhat from supplier to supplier. Two features should be considered when deciding which one to buy. First, the best dividers are made of shiny stainless steel. As a result they will reflect engine heat back to the outside of the box, so the cool air coming in from outside the car doesn’t get heated up before being pulled into the supercharger. Second, the divider should have good space all the way around, so that air can flow into the entire surface of the filter without any restrictions.

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.

If you own a Cooper model, you can still make improvements in air flow into the engine. A less-restrictive reusable flat filter is available for about $50 to replace the stock filter. Aftermarket developers have also re-engineered the ram air intake duct and air box cover to improve air flow. Installing this improved ducting system in conjunction with a reusable high-performance flat filter will cost about $200 and make a measurable improvement in your Cooper’s horsepower.