Brakes rotors come in 2 basic designs. Solid, and vented. All 320i's came with solid rotors after 1977. Grooving rotors can be done to either style, as can cross drilling. These are tricks done on race cars to help vent gasses quicker, and reduce fade. Very useless on a street car. Vented rotors are the way to go. 77 320i's had vented rotors. You can get the rotors, pads, and calipers from a 77, and bolt them on your 81. It makes a big difference. The adavntage of vented brakes is theat they dissipate heat much faster. HTH,
Al- 77 brakes on my 79

My 1981 320i USA model needs new front brake rotors (the first in 20 years). In Bavarian's catalog, I see several choices: solid, slotted, grooved. The latter two are more expensive. Please forgive me if this is a dumb question, but what advantages are grooved or slotted rotors? I examined the rotors on my 1999 Volvo V70, and it has solid rotors. Thanks for the information!