Let's take a minute to understand how a base valve effects the shock and how it improves performance in the race car. First lets look at the base valve and see if we can understand how it works. As you can see it is a fixed piston with shims on both sides of the piston, one side to controls compression and the other side to controls rebound. The base valve needs to be fixed in the tube so it can control the pressure being built on the compression stroke of the shock. You need to understand that when a shock is moving it is making a hydraulic force greater than what you would feel by hand and it is this force that we need to control. Under normal conditions the divider piston and gas pressure would control this pressure, and as the compression pressure goes up so will the gas pressure in the shock. This is true in a normal gas shock, but in a base valve shock the base valve will control the pressure allowing for much less gas pressure in the shock.
In conclusion a base valve in the shock will head off the high pressure oil that is generated by the main piston and this will allow you to run lower gas pressure in the main gas chamber. When done correctly it will increase your feel and grip in the race car, but when done wrong it will make the car more ridged in the rough. Not all base valves are made the same and some only work on a really smooth surface so you need to do your research before buying. The old style twin tube base valves are not designed to handle what we are going to put it thru in order to race in today's market. So make sure you understand what a base valve is going to do and how I is going to work for you and your car.