If you own a BMW 325i and would like to increase the horsepower output of the vehicle, there are a number of ways you can achieve that. The BMW 325i is equipped with several performance parts when it is manufactured; however, the car will follow factory specifications unless the owner makes aftermarket changes on his or her own.
Use additives in the coolant. Certain products, such as wetting agents, will reduce the temperature of the coolant before it enters the engine and thus further decrease the temperature in the engine, allowing the car to run at higher horsepower.
Hire an auto professional to upgrade the spark plug wires on the car. The stock wires, while fine for normal day-to-day activities, are not meant for high performance. Performance spark plug wires help lower resistance within the engine, minimise electrical interference and allow the engine to put out more power.
Replace the air filter. An aftermarket product will block more engine heat and keep the engine cooler at all times, allowing the engine to run harder. As with the spark plug wires, hire an auto professional to do the upgrade.