When you are trying to get more horsepower out of your engine there is one key thing to remember. More air = More power. Your engine takes in air and fuel (Either gasoline or diesel) then uses a fixed percent of air to fuel ratio then uses a spark to light it and give you power. There are several ways to add more air to your engine that I will talk about. And other ways to add power also.
Cold air intake. Cold air is more dense than hot air. Therefore you get more air into your engine. A cold air intake takes the intake out of your engine. After your engine has been running for a while it gets hot, very hot, and when you take it out of the engine you get more air. This also adds to your gas mileage.
Supercharger, or Turbocharger. Both a Supercharger and a Turbocharger do the same thing, only in a different way. They both force air into the combustion chamber above atmospheric pressure. The supercharger is powered either mechanically by belt or chain drive from the engine's crankshaft. A turbocharger is powered by the mass-flow of exhaust gases driving a turbine this causes a lag where you get little to no boost while your waiting for the exhaust to exit the engine. Both of these can have horsepower increases from 50-100%. But when you are getting boosts past 10psi you are probably going to have to add an intercooler and use higher grade fuel. And you will want to enforce your engine with stronger parts.
New spark plugs. Next time you get a tune up, see if you can get some performance spark plugs to put in your car. Some platinum or iridium spark plugs will light all the fuel in your car faster and more efficiently so that you have more horse power.
Aftermarket cat-back exhaust. Reduces back pressure of the exhaust in your car increasing horsepower and improving fuel efficiency. If you do not want your car to sound a lot louder then do not go with glasspack exhaust or anything like that.
Aftermarket headers. This also has to do with reducing the back pressure of the exhaust. If you already have a cold air intake and an aftermarket cat-back exhaust system then you will feel the power this gives you.
Performance tires. You can have all the power you want coming out of you engine. But if you don't have any grip from your tires then your not going to feel the power.
New chip. Watch out this is where a lot of people get scammed. Engines are having more and more to do with electronics. Your stock chip in your car is made for the average driver and it isn't using the right fuel to air ratio. This will show best results when combined with a cold air intake.
