Tuesday, November 20, 2012
When Going Faster becomes a Passion: Competition Upgrades for Your MINI (Part I)
When you get to the point that you want to take your MINI driving to the next level and get seriously involved in auto-crossing and track events, you’ll need to add some safety gear to the car to meet most organizations’ requirements. Also, as you reach a point in your driving ability where you’re starting to reach your MINI’s limits of acceleration, handling, or braking, you may also want to make some mechanical upgrades to improve the car’s performance.
Either way, the aftermarket suppliers have just what you need. In this chapter, we’ll discuss means of further increasing your horsepower and response, gaining stopping power and improving the MINI’s handling. We will also discuss how you can meet the safety requirements of your racing organization if you have decided you want to take your MINI out onto the track for some serious competitive motoring.
Finding Even More Horsepower
By now, in your desire for more power, you have changed out the air intake, remapped the ECU, replaced the Cat-Back exhaust system, and replaced the supercharger pulley if those changes are permitted by the group that organizes the events in which you participate. In addition, you may have replaced the spark plug wires, added a spark booster, and installed a water-to-air inter-cooler to increase your net horsepower for enthusiastic driving.
Be assured, there are still more parts on the shelf that will help you get the maximum available horsepower out of that sturdy four-cylinder engine under your hood. You can substitute a high-performance camshaft and if you’re really serious, replace the cylinder head to improve the engine’s ability to breathe. If your car is going to be used just for track or autocross competition or you’re willing to do a little work before big weekends, a high-flow exhaust header and catalyst can give you a solid boost in performance.
The MINI engine has what is called a “single overhead camshaft” (abbreviated SOHC). The camshaft is the component on the engine that is connected to the drive shaft by a roller timing chain (it looks like a bicycle chain) and rotates with the crankshaft to cause each of the intake and exhaust valves to open and close at the right times. The MINI uses a single camshaft to control both intake and exhaust valves on all the cylinders, and it is mounted in the top of the engine, so it is called a single overhead camshaft.
The actual camshaft consists of a shaft that runs from the front to the rear of the engine. On this shaft are mounted twelve cams, three for each cylinder. As these eccentrically shaped cams rotate on the shaft, they push on two rocker arms for the two intake valves and a dual rocker arm for the two exhaust valves on each cylinder, causing the intake and exhaust valves to open and close. A high spot on the cam pushes the valve open, and then as the cam continues to rotate, the lower spot allows the spring on that valve to push the valve closed.
As the intake valves open, they allow the air/fuel mixture to enter that cylinder. As the intake valves close, the exhaust valves open, allowing the combustion gases left after the explosion to escape from the cylinder.
By changing the size and shape of the cams, it is possible to change the points at which the valves open and close, and the time during which they are open. Consequently, changing the camshaft is a standard way of upgrading the performance of an engine. A camshaft that causes the valves to stay open longer is said to be “hotter”—producing more power—than one that does not allow as much time for the fuel/air mixture to enter the cylinder, or the exhaust gases to escape.
The trade-off here is that additional horsepower can only be gained by negatively affecting the smoothness of the engine operation, especially when idling, so a hot cam is often said to be “lumpy.” To some extent, the design of the camshaft also has a negative effect on gas mileage, since more fuel is allowed to enter with each rotation of the engine.
As one might expect, there are several different variations of cams available, with the hottest being very good on the race track, but totally unsuitable for street use. However, there is a middle ground with several aftermarket camshafts that have been engineered to provide better engine performance without noticeable negative effects on the smoothness of the engine. These camshafts are ideal for the MINI that is used primarily for street use by an owner who would also like improved performance for occasional track days and autocross events.
To select the one that’s right for you, rely on the advice of an established supplier and tell them what your objectives are in replacing the camshaft, as well as what else you have already done to the car. It’s possible they may be able to recommend other changes that you can make to increase performance and horsepower before going to the expense of buying and installing a new camshaft. If they think a higher-performance camshaft is the right answer, they should be able to recommend one that will meet your goals.
Replacing the stock camshaft with a high-performance camshaft is an effective way of improving engine performance while still using stock valves and valve springs. This way, engine performance can be improved without the expense of disassembling the motor and changing the cylinder head.
A high-performance camshaft typically is available for the Cooper S for about $500 and for the Cooper for less than $600. In both cases, there is generally a core charge of about $100 which is refunded when the original camshaft is returned to the supplier. Installation should only be undertaken by an experienced professional shop.
Next Installment: Competition Upgrades for Your MINI (Part II) - High Performance Cylinder Heads
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