About the code which _Ro posted above, it controls how fast each of the 3 Mini-Turbo types is charged, separately.
(I could swear that there's a thread in the site which teaches how to port codes to other regions)
NTSC-U
048B1400 vvvvvvvv
048B1404 xxxxxxxx
048B1408 yyyy0000
048B1278 zzzz0000
vvvvvvvv = The lower the value, the faster the blue Mini-Turbo charge.
0x00000050 is faster than vanilla, but it looks balanced enough.
0x00000000 results in an instant charge.
xxxxxxxx = The lower the value, the faster the red Mini-Turbo charge.
0x00000050 is faster than vanilla, but it looks balanced enough.
0x00000000 results in an instant charge.
yyyy = Probably a MT/SSMT charge multiplier, the higher the faster.
It works in tandem with vvvvvvvv and xxxxxxxx, in case these 2 values are set too high.
0x0001 is the minimum value
0x0000 keeps the drift mechanic, but disables both blue and red MT charges, effectively disabling Mini-Turbo.
You can do the above if you want to make a Super Mario Kart-styled distribution, for example.
If you want, you can delete the entire line 3 (048B1408 yyyy0000) and only use xxxxxxxx and yyyyyyyy to set the MT/SSMT charge speeds.
zzzz = The lower the value, the faster the Stand-Still Mini-Turbo charge.
0x0014 is faster than vanilla, but it looks balanced enough.
0x0001 results in an instant charge.
0x0000 causes a bug, you can solve it by re-starting the race.
if you want, you can replace zzzz0000 with a 60000000 (nop), doing so keeps the burnout mechanic, but disables the SSMT charge
The above effectively disables Stand-Still Mini-Turbo, you can do this for balancing purposes, for example.
That's it, have all a good day