INTAKE / FILTER - One of the areas that most cars could use some improvement is the intake and filter, since manufacturers have noise restrictions and costs to consider. Many companies, K&N being the most famous, offer OEM replacements, as well as conical filters that replace the entire air box. For a little more money you can just replace the entire intake, however. The one pictured is a so-called "cold air" intake (versus a "short ram"), which relocates the filter lower in the engine bay for access to hypothetically cooler intake air (but be careful of standing water). The filter alone will help your engine breathe better over the stock (read affordable) paper filter plus give it a throatier sound. HEADER - Headers are a tubular replacement for OEM exhaust manifolds, primarily providing larger diamter tubing for higher air flow. There are two configurations for a 4-in-line engine: 4/2/1 and 4/1, with the numbers referring to the number of pipes leading to the collector. Each type provides better results depending on the type of engine and who you're asking. Working in conjunction with a cat-back exhaust will yield the best results. Many import four cylinder engines are already highly tuned, and therefore wringing more power out of them is not the easiest thing to do. An additional benefit is that you'll save weight over a typical iron OEM manifold (some OEMs are tubular however). EXHAUST - Most OEM exhaust systems are relatively restrictive, so replacing them is usually a good idea. There is a noticeable improvement in power to be had, plus the aftermarket units usually look better than stock systems. (Don't overdo it though. Seriously.) Exhausts can be had as muffler only, axle-back, or cat-back. Many people go with a cat-back system, meaning everything aft of the catalytic converter is replaced. A high-flow converter might be a good idea as well, as long as you don't mind dealing with an occassional CEL. Many aftermarket exhausts are noisy, so it's really just a matter of how much you crave attention and how easily you get migranes. And don't put loud mufflers on autos! HIGH FLOW CAT - Catalytic converters basically take the exhast gases from the engine and convert them into gases that are more acceptible to the atmosphere and liberals. They do bottleneck the exhaust more than a test pipe, for example, but don't get caught without your cat unless you enjoy paying fines (plus you typically only get a few horsepower anyway). A better solution is a high flow cat, which restricts the exhaust less than a stocker. Another reason to go with an aftermarket cat is if you upsize your header and/or exhaust, which can be up to 3" in diameter. Technically you aren't supposed to replace your cat unless it is defective, so be creative. Be sure to hold on to the stock unit just in case. UNDERDRIVE PULLEY - The use of underdive pulleys is a clever trick to gain horsepower back from the engine that is being lost parasitically. The pulleys are referred to as "underdrive" because they cause the item they are attached to, such as the power steering, alternator, or even the air conditioning, to spin more slowly via the pulley being larger in diameter than the stock pulley. Some supercharger owners use a similar trick, only in reverse, to make their supercharger spin faster than normal and produce more power (be careful). You might recover a few horsepower using this method, but installation can be a bit tricky. We suggest you consider calling your favortie shop on this one. SUPERCHARGER / TURBO - Superchargers and turbochargers are like brothers, or at least cousins. Both are called forced induction, meaning they force more air into the engine, resulting in a more powerful combustion stroke (both require additional fuel as well). How the two go about their business is fundamentally different, however. Turbos are driven by exhaust gases and must overcome inertia and spin up to speed as the flow of exhaust gas increases (turbo lag). The exhaust spins a turbine, which in turn compresses the incoming intake charge. Turbos can yield alarming horsepower increases but offer little low end torque, usually require engine oil for lubrication, and typically demand more of their owners in the way of tuning. Supercharges, or blowers, are connected directly to the crankshaft, allowing them to provide useful performance increases even at low engine speeds. There are three types -- roots, screw, and centrifigal (basically a crankshaft-driven turbo). Many blowers are sealed and therefore do not require engine oil. Blowers provide useful torque increases and tend to have better long term reliability. Intercoolers of various types are often used with forced induction to lower the temperature of the intake charge, which heats up as it is compressed. Stay off the rev limiter, though, as it will cause the engine to run lean and potentially cause severe damage (like an ejected piston). COMPUTER - It would be great if cars came tuned for performance from the factory. The fact is they typically aren't, and once you start monkeying around with modifications, being able to tune your engine will provide more power and, more importantly, extra security against expensive failures. Units range from simple air/fuel mixture adjustment to variable valve timing adjustment to boost control. Some people have even been known to use them to help pass emissions, but we wouldn't know anything about that. The best way to go is to dyno your car when it is new/stock to get a baseline. Then add your modificationss, take it back to the dyno, and have it tuned by someone that knows what they're doing. CAMS - Cams are what open and close the valves inside the head. Variable valve timing (such as Honda's VTEC system) provides multiple cam lobes for low and high rpm, which is what allows the car to idle so innocently yet go like stink at high revs (evolutionary setups that are continuously variable are becoming the norm). Several companies offer aftermarket cams, or you can simply raid the corporate parts bin. Basically cams control the lift and duration of the valve opening, and the hotter the cam, the more air and fuel the engine can digest. Depending on the application, it's a good idea to also replace the valvesprings and retainers as well to make the valvetrain bulletproof at high rpm. ADJUSTABLE CAM GEARS - The cam gears are what connect the crankshaft to the cams via the timing chain or belt (that thing you should never ever let break on an interference enginebecause if the timing belt breaks, the pistons crash into the valves). By making the gears adjustable, it allows you to either advance or retard the timing and fine tune the engine for your setup, whether it's all motor or boost. Be careful though, because if the cam gears slip at all, you'll potentially be rebuilding or replacing the engine (back to that interference thing again). The K series Honda engines, among others, now have continuously self-adjusting cam gears, making this something of a moot point. OIL PAN - The idea behind a performance oilpan is to prevent the oil pressure from dropping due to oil shifting during high centrifugal forces. Long, high speed, high rpm corners at the track can easily cause this. Oil pressure is especially critical in the high revving motors typically found in sport compacts. Another goal of an aftermarket pan is using baffles to keep the crankshaft free of excess oil (or windage), which allows the engine to spin more freely and achieve its full power potential (also very important with high revving engines). No horsepower gains here, just some insurance against engine damage or failure. Some worthwhile modifications can't be shown off at local meets. THROTTLE BODY - A nice compliment to an aftermarket intake is a larger bore throttle body. The throttle body is what sucks the air into the engine via the intake. The larger the bore of the unit, the more air it is able to provide. The combination of the two can get pretty loud, though. The harder you step on the gas pedal, the more the butterfly opens up. This, in conjunction with the hot cam in a lot of sport compacts, means lots of decibels at full throttle. Then again if this bothers you, you probably should have bought something else. Getting the ECU to cooperate with the additional air flow can sometimes be tricky, but you can expect to see a few horsepower in the meat of the powerband. SHORT SHIFTER - Some cars are known for having precise shifters with short throws (snick-snick); others are known for having rubbery shifters with long throws. A simple fix is a short shifter, which not only shortens the throws between gears, but also stiffens up the feel of the linkage. As one source puts it, "Any time that you spend shifting is time that you aren't on the throttle." Plus there is something to be said for the tactile experience of changing gears for yourself, which should be enjoyable and rewarding. And don't forget a sweet new shift knob to go with your shifter. We suggest a direct replacement - no allen screws! A short throw shifter can't take the place of a well designed transmission, however. CLUTCH - If you haven't yet smelled the lovely odor of your clutch when you mistreat it, don't worry -- you will sooner or later. Like the other OEM parts, the clutch in many sport compacts is designed to handle the normal every day stresses of the stock engine. As you add more and more power (and likely drive it harder and harder), some of these stock parts start to complain, and in the case of the clutch -- slip. You have a couple of options: an aftermarket clutch or back to the corporate parts bin. Aftermarket units vary widely, with some feeling pretty close to stock and others requiring several reps of leg curls at the gym to operate. While the engine is apart you might try a lightened flywheel as well.