Hello everyone I am an owner of Volvo S60 from 2011 with D5 engine 205hp and manual transmission. I really don't like how short the gears are and how high the engine's revs are on a motorway so I was thinking about changing the final drive ratio. Any advices would be appreciated. I checked the Volvo website and it looks like the manual transmission has 4.0 ratio, while the automatic transmission has 3.2 ratio. I am wondering if they are interchangeable? I made some calculations and it looks like with that ratio it will suit my needs. I was also thinking about swapping the 6th gear I don't really use 5th gear at the moment, so basically was thinking about making the current 6th gear to become 5th gear and a modified one to be 6th gear so I can cruise at lower RPMs and get a better fuel economy. I don't know which option should be easier to achieve and which will be cheaper.
Any advices if someone has done something similar are appreciated. The car is FWD I know it is way easier on a RWD cars.