I am looking for 411 from anyone who has installed a K & N filter on a 1999-2001 Passat 1.8T. Looking to find out if there was a noticeable horsepower increase and if it had any effect on the exhaust note.

If you are really in tune with your car, then you might notice the slight HP increase the K&N stock filter replacement would give you. You might notice it is a little louder but it shouldn't effect your exhaust note. Their may be a tiny bit more engine noise too. For real gains, chip your car. That's when the filter really helps.