Ok, I bought a 2002 525i. Went with smaller engine for better gas mileage, I commute 1000 miles per week in this car. Any upgrades (like K&N), etc. that I can do to increase performance without compromising mileage.

Well since it's a V6 first you can upgrade your chip which can give you anywhere between 13-35hp, changing the air filters can give you around 3-6hp and getting a good exhaust system (full not just the tips) which might cost a bit can give you around 8-12hp or even more not sure. So if you get all of them and they would work together and give you around 50hp plus. Your car is 195hp I think so you'd have a 245/250hp car now and it would make a hell of a difference I'm telling you. A 530 of the same year has 231hp and a 540 has 290hp so your car would be pretty fast!

Good Luck

i don't have a 5 but here are a couple sites to help you
andysautosport.com
cardomain.com

Actually as you know as the owner the car is an In-line-6 not V6 an the car has 184 HP not 195. The 530 has 225 not 231. You will gain power and MPG savings slightly by some performance modifications. The best would be a software download "chip". There are ones that give you more power than Dinan (dinancars.com) but not the MPG savings if you drive conservative. Jim Conforti's company with the Shark Injector will give you better horsepower upgrades but not the as good of MPG. Good exhaust companies are www.UUC.com, Active Autowerkes www.aa.com, Dinan www.dinancars.com. Many BMWCCA members don't like B&B because Billy Boat's company doesn't put all of their research and development into BMW like these others. They make exhaust for most brands and don't put the BMW specific effort that the others do.