the breakdown points of the oils are different, if you feel your driving is more aggressive then suttle, i suggest get the heavy. i run heavy in my turbo classic and have nothing but good to talk about. the heavy uses a red color oil and the light to the best of my knowledge uses a blue color, i dont think mixing would be a good idea. but then again i may be wrong. i say use the heavy to be on the safer part. and if you have to order it, it would be a good idea to order the gallon i think it is, it will be cheaper then buying 4 seperate quarts i think.