Hey guys. It's time to fill up on new oil. I have no idea what oil the car is currently using, but i want to put some fully synthetic oil in, castrol preferably. (sounds the part) Is it ok to mix fully synthetic oil with a different oil? or if not, what oil would you recomend for my 1.6 driver (carb) 1989. Im looking for something which will add performance (i heard a decent oil adds up to 5bhp) and something that will lubricate my engine REALLY well seeing as i spend most of my time on the high revs. any recomendations??