Far as I know mate, fans only really do anything well the car is bellow say 20mph so if you have no over heating problems well she is on tick over I wouldn't bother, also if you mean a slimline at the back of the rad between turbo and rad I would think it would be really tight and with one pushing from front and one pulling from inside I sapose they would have to have the same flow rate, I'm not really sure, one of the lads on here will know I would of thought tho, maybe two slimlines on the front would be better than one big one?? Cosmetically they look smarter just peaking through the standard bumper but that's just me, some lads like to keep it as standard looking as poss