us the senthetic in every thing on the car all I use in mine is amsoil in the motor and gear lube rearend, t.c., and tranny. just make sure you get a oil flush kit when you change it over to get all the non senthetic broke down and totaly out of the motor
mark
at tkrPerformance

I had my gsx using non-senthetic mobil 10w30 untill it rached 50k then I switched to mobil 10w30 full synthetic I didnt do a flush havnt had any problems yet (84K now).

There is one possible problem that could result from switching to synthetic oil. When an engine uses regular oil for a long time the thicker regular oil forms a kind of seal on gaskets. If you switch to synthetic the thinner oil can seep through your gaskets and cause oil leaks but its not garanteed to happen also if your car has many miles on it you might get slight lifter tick from the thinner oil.

One more word to the wise
Never use synthetic oil on a new or freshly rebuilt engine until after the first 5k miles because it wont break in right and will take away from the life of the engine