well my ka puts out high pressure so the bigger the line the less pressure im seeing with better oil flow . garrett suggested the 6an line for such a big turbo . borg warner is also recommending 6an too now . def dont need 6an stuff for 300zx tt setups . I may try using the 40micron fuel filter for my oil feed . being i have a 6an and the filter having some restrictions i should be alright ,Rather than having a 4an with a filter . My turbo is journal bearing btw