you might need to harden up your front end as when your front end drops under brakes and you turn the whole car pivots across the diagonally opposite wheels. back pressure with your exaust only saves your valves and deminishes power so you get more power out the manifold as apposed to a full system but your system might be a bit big. what size motor is in it? softening up the rear by removing the overload springs only softens it up after a certain amount of travel as they are only designed to work after they are carrying a load.