A good way is to make the own little mod that does that thing. Download DeAR 2 from
here, extract the archive where you want and run the program. After, open the file mm2core.ar placed in the main game folder clicking on Browse button, then click on List files button, and then seek for the tune/vehicle/vpbus.vehcarsim file; select it, click Extract button, and close the program. Now go into the main game folder and there you'll find the folder named "tune" with the folder named "vehicle" with the extracted file in it. Open that file with Windows Notepad, look for the MaxHorsePower, Low and High values which are the responsible for the vehicle acceleration and maximum top speed. Increase these values as you want and save the file by closing Windows Notepad. As final things to do, go back to the main game folder, select the "tune" folder and create a ZIP compressed archive with WinRar or 7-Zip (this last is mostly suggested) calling it something like "!!!!!citybusmod.ar". As last, delete that folder, leave the created .ar file in the main game folder, and run the game to check your change done to the default City Bus.