Upgrades on 1990 horizon-omni?

I have a 1990 plymouth horizon with many omni part its looks great we re-did the entire car but i want more speed and power. I wish to not go as far as getting a new engine but just want to know what I should add to it for speed. The specs are 2.2L / 4 Cyl / Front wheel drive / Automatic (but i have the part to switch it to manual). It comes stock 93 horse power ,but we have changed some things.