While there is no way to increase horsepower without spending money, there are a number of ways that a car owner can increase horsepower. This includes changing the computer chip in the car, installing polished intake manifolds, allowing exhaust to exit the car easier and changing the heads and cams of the engine.
Changing the ROM chip in the engine control unit often increases the performance of a car. Chips for most cars can be purchased from aftermarket dealers. Reading independent reviews of these chips are important before installing them, because some offer little-to-no performance enhancements compared to factory-installed chips, according to HowStuffWorks.
When a piston moves down during the intake stroke, air resistance reduces power from the engine. This is why some modern vehicles use polished intake manifolds, which reduce the amount of air resistance the pistons have to work against. Polished intake manifolds can be installed on cars that do not already have them. Buying new piston heads and cams for the engine can also improve airflow in a vehicle.
Air resistance from the exhaust system of a vehicle, also known as back pressure, can rob engines of power. Back pressure is caused by small exhaust pipes or mufflers. Installing big tail pipes or free-flowing mufflers reduces or eliminates back pressure altogether.