4. Performance Intake Systems
If the performance gains from intakes are so easy, you ask, why don't they come equipped with them from the factory? Consider the overriding development mantra of "NVH" that manufacturers are working under today. Noise, vibration, and harshness are the supreme evils singled out by most new-vehicle engineers. Performance is often sacrificed in pursuit of providing the quietest, smoothest vehicle to the customer.

Although most of you reading this probably enjoy the healthy honk of an open intake under the whip, the manufacturers have surmised that 90 percent of the public finds this noise offensive, so they strangle the intake tract in the name of smothering NVH. Since the engine has to overcome these restrictions when inhaling, it often reduces the overall efficiency of the motor.

5. Performance Exhausts
The reason vehicles aren't equipped with performance exhausts from the factory follows the same rationale as with intakes. The mass market wants their transportation quiet and smooth, but most red-blooded enthusiasts would rather hear the melodious baritone of a well-tuned V-8 burbling through a free-flowing exhaust system.

There are many different systems on the market employing different construction techniques and engineering philosophies. Most factory mufflers are of the "chamber" type, routing the exhaust through multiple chambers before sending it out the tailpipe. A freer-flowing variation on this design has been perfected by several aftermarket manufacturers and provides a throaty sound that has made it a favorite among many enthusiasts.

Many performance mufflers also employ a straight-through design. Basically, the muffler is a straight section of perforated pipe surrounded by sound-attenuation packing. This design is well-suited for vehicles equipped with a supercharger or turbo because it reduces backpressure and lowers exhaust temperatures. Most of the better systems on the market have been dyno-tested to offer a performance increase in the most commonly used rpm ranges.

6. Premium Fuel
It is common knowledge that higher-octane gasoline increases fuel efficiency. However, from a dollar standpoint, the numbers may not justify filling up with "high-test." Premium fuel can be more than 20 cents a gallon more than 87 octane. On a 30-gallon tank, that's $6. If you fill up weekly, that's $24 a month. Probably not the difference between making the rent or sleeping in your truck bed, but it's enough for two large pizzas. Unless your owner's manual specifies premium fuel, or your vehicle is equipped with a turbocharger or supercharger, you don't really need premium fuel.

7. Lubricant Enhancers
This crowded segment is rife with competing claims and different manufacturers doing various "bearing" tests and pouring sand down the oil filler cap. Some of the more cynical sages in the industry have called these modern-day snake oils. Though it's unlikely you'll see an additional 3 to 5 mpg from merely pouring in a bottle of lubricant enhancer, none of them is likely to harm your engine. At $20 to $30 a bottle, you can afford to experiment with different products for best results. However, do not mix lubricant enhancers. Wait until the next oil change to pour in a new enhancer. Be careful not to exceed your engine's crankcase oil capacity when adding an enhancer. An overfilled crankcase can lead to foaming and inadequate oil pickup, which will cause far more damage than any good you might get from an enhancer.