I own a 95 BMW 325i sedan. It has pretty good accelaration to me.. Also, the specs for my car are below, straight from Edmunds.com, not sure where u got the 22 mpg for highway, but it doesn't apply for my car. (reference 28 mpg below on hwy).. I'd say if you want a cheap way to increase HP, buy a cold air intake.. easy to install, and it'll make the engine sound bigger.. I did this on my Hyundai Tiburon 03 (Injen CAI RS) and it added about 12 HP plus it sounds like a meanier engine now.. cost me $199 off the net.. They make short ram intakes but I wouldn't waste my time honestly, get you the real deal.. But i dont think your going to find a sure fire way to increase fuel efficiency.. just make sure the car is tuned up.
Acceleration (0-60 mph): 7.8 sec. Base Number of Cylinders: 6
Base Engine Size: 2.5 liters Base Engine Type: Inline 6
Horsepower: 189 hp Max Horsepower: 5900 rpm
Torque: 181 ft-lbs. Max Torque: 4200 rpm
Drive Type: RWD Turning Circle: 34.1 ft.
Fuel Tank Capacity: 17.2 gal.
EPA Mileage Estimates: (City/Highway)
Manual: 19 mpg / 28 mpg Automatic: : 20 mpg / 28 mpg
Range in Miles: (City/Highway)
Automatic: 344 mi. / 481.6 mi. Manual: 326.8 mi. / 481.6 mi.