dirty drive tuning provides a increase of the optimal mutliplier, which translates directly as a percentage increase of speed.
top speed of an unmodified FDL is 302 m/s straight line speed and 406 boost speed.
fancy secondaries aside, that optimal multiplier increase of DD G5 tuning caps out at 29%.
302 * 1,29 = 389,58 m/s
406 * 1,29 = 523,74 m/s
i personally got drives with fancy secondaries resulting in a 33% increase, if you get those for your FDL, it wold go
302 * 1,33 = 401,66 m/s
406 * 1,33 = 539,98 m/s
for comparison, my cobra mk III does 579 m/s boost speed with dirty drive tuning, and my courier with clean drive tuning 712 m/s