When you install a modification in a vehicle in a mod garages, and use any of the methods that can teleport you out (gyms are the most convenient method), every vehicle will have those same mods installed when you press the "exit vehicle" key. You can hold the handbrake to avoid exiting your vehicle when pressing this and have the modifications applied to it. Bass boost and hydraulics are useful modifications because after they have been installed once, you wont be allowed to install again on the vehicle you are using for the IL run.
Note: Be careful, installing nitros on Bikes will crash the game.
The GTA:SA community has been deteriorating over a long period of time. Many top runners are not currently present on the leaderboard. This issue has not been seriously addressed yet, but an attempt will be made to remedy it now.
As of this news post, the San Andreas leaderboard will function in