A mate at work did a lot of work to his Patrol.
1st up, he cut the baffles out of the stock exhaust, then got a 3" system and couldn't give the old system away. I ended up chucking it in the recycling skip for him.
He then went a larger front mounted intercooler, modified air box and a chipped it.
It goes like a cut cat now, not as good as the BT50, but OK
, a lot more torque lower in the RPM range than standard. He is still having issues with it and it occasionally throws codes and has to be re-set, so it is a work in progress.