Air Flow - The Critical Path For More Power From Your Car
One of the keys to more power out of your car is getting air into and out of the engine in the most efficient manner. You will want the maximum amount of air coming into the engine, because the more air in the combustion chambers mixed with the correct amount of fuel will result in the maximum power being developed. In the same fashion once the combustion has taken place you want the maximum amount of residual air/fuel gases out of the combustion chambers so that new air/fuel can come in.
So what can slow down the flow of air in and out of your engine? A variety of different designs and components go into a stock car that was not created with maximum power in mind. Remember that the car manufacturer is making a variety of trade-offs when they design and build a car. On one hand they must keep their costs as low as possible, which means that the parts they install might not be the best brands or designs available. They also must appeal to a wide audience in order to sell the most cars. One way is to keep the car as quiet as possible. Unfortunately many of the things they do for keeping sound down also keep the engine power down.
On the intake side of the engine the following things can slow down the air flow and decrease potential power. Starting with the outside air is the air filter. Paper air filters can block out air flow along with the particles you don't want in your engine. The next item is the throttle body. This device controls the amount of air being drawn in. If it is the wrong size or has restrictions, the air flow is slowed down. Following are the plenum, runners and intake port. Stock devices are usually not as smooth internally as possible and they can cause further restrictions. So on the intake side, have a very effective air filter, followed by the minimum restrictions in the path of the air flow into the cylinders will help maximize the power potential of your engine.
On the exit or exhaust side of the engine we find the exhaust headers, the catalytic converter, various pipes and mufflers and the exhaust tailpipe. The exhaust headers lead the exhaust gases out of the engine. If not designed correctly they can restrict the exhaust gas flow. This might leave some wasted gas in the engine cylinders at the time new fresh air/fuel is being brought in to the cylinders. There is only some much room, and any space taken by exhaust gas that remains means less incoming air and fuel, and hence less power. Because of environmental laws there is not much you can do with the catalytic converter, just kind of accept what you have. However, you can get mufflers and pipes that minimize the exhaust gas restrictions and increase the power of your stock engine.
Each one of the devices mentioned above can be replaced with more efficient products, and in many cases stock parts can be reworked to improve efficiencies and raise potential horsepower.