A turbo won't change the gear ratios, but it makes it so you have a little more power so can stay in higher gears at 80KPH at lower revs and not have to change back to third. (depending on the type of turbo selection of course).
The down side is that the factory 4BD1-T engines are different to most 4BD1 in the Perentie 110, because the 4BD1 don't have oil squirters under the pistons. So while it's relatively easy to bolt on the turbo manifold and a turbo, there is increased risk of piston meltdown. Even Dinty experienced meltdown on a non turbo 4BD1.
