How to Upgrade the Performance of a Subaru Forester

Clean out your car to get rid of any excess weight -- even the spare tire if you can do without it. Removing unneeded items decreases the weight of your car, which increases your gas mileage.

Get regular oil changes and when you do, use synthetic oil. Synthetic oil lubricates the engine better, allowing for better wear protection and friction reduction on the vehicle engine. Use a high-performance oil filter to allow for a higher oil pressure rate.

Use additives in your vehicle's coolant reservoir that keep the coolant cooler. A product called Water Wetter, for example, reduces the temperature of the coolant by 30 degrees Fahrenheit, which allows for better heat transfer and optimum engine efficiency. A coolant additive also helps prevent engine corrosion and rust.

Change your spark plugs to performance spark plugs. Upgraded spark plugs usually have a platinum tip that allows for a better spark. Switch to high-performance spark plug wires also for a stronger signal to your spark plugs. These changes will improve gas mileage by allowing your engine to create better combustion.

Install a cold-air intake kit and a high-flow air filter. Installing a cold air intake allows for smoother air flow into the engine, which increases engine power. Connect flexible intake tubing from the cold-air intake filter to an area behind your front headlight or below your vehicle's grille, where there is an opening that the tubing can be connected to. Install a mesh screen into the tubing to prevent particles from being sucked through while you are driving. Install a turbine into the air tubing between the intake tube and air filter. The turbine sucks air into the intake tube in a twirling forced motion, giving your vehicle added horsepower.