Low-end: * High Performance Air Filter. K&N f.x. are good. (less resistance - In) * Look into OBC software tweak/upgrade. * New exhaust (less resistance - Out) * High performance spark-plugs * Run on 98 octane - if available * Upgrade fuel-filter > again: less resistance. * Oil-filter also. If you are up to it, look into Prolong Oil. It's the best I know of. *** High-end: * Turbo. * Aero-dynamics depending on power-output. * Brakes to follow if applicable. Not an easy nor cheap solution. The entire system needs to be upgraded to accommodate. Depending on your enthusiasm for the car (seeing it's age), and on your location, it's oft better to buy a new one. *** The first mentions above are a must in my book, and I pretty much add these to a new car regardless. Long-term: More power, less fuel-consumption. We're talking at least 10% on both. One example, I reduced fuel-consumption on an old (rugged) E28 by more than 25% by simply switching to Prolong, and adding some in the fuel-tank as well. (semi-bad example: the engine was whack. Needed a new carburetor.) And of course: service the engine from time to time, and make sure brakes don't hang (unnecessary friction).