Affordable ways to increase horsepower include upgrading the vehicle's cold air intake, adding a throttle body with a bigger diameter, changing the exhaust header and using high-flow catalytic converters. Employing a high-flow cat-back exhaust system is another way to increase a vehicle's horsepower.
The most affordable way to increase horsepower is upgrading the cold air intake. Engines are powered by a mixture of fuel and air, and aftermarket cold air intakes have a larger surface area that allows more air to pass through. Similarly, changing the throttle body to a larger diameter gives the engine more access to air and increases horsepower.
Changing stock exhaust headers can increase the horsepower of a vehicle for a relatively low cost. Headers come in two styles. Short headers are best for increased horsepower in a car that is driven daily, as the rpm range associated with these headers is low. Long headers increase horsepower the most, but they often present problems with emissions and cause the check engine light to deploy unnecessarily.
High-flow catalytic converters speed the reduction of emissions. They also increase RPMs, so horsepower increases as well. However, these are not legal in all states.
High-flow cat-back exhaust systems are on the pricey side but are still an affordable way to increase horsepower. This replaces stock mufflers and exhaust pipes to improve air flow.