In my opinion one of the first major modifications you should do to make your quad race ready is suspension.  You can have the most built motor in the world but if you cannot get the power to the ground it is pretty much useless.  A good place to start for the more moderate racer is a +2” standard travel a-arm kit, with performance shocks or rebuilt stock shocks; as well as a performance or rebuilt rear shock.  This is relatively in expensive and a good place to start if you are new to racing.  When the time is right you will want to upgrade to a long travel a-arm setup as well as a long travel swing arm. 

When going to a long travel setup, there are many popular manufactures to choose from.  Walsh race craft, Leagers, Houser, Lonestar, ASR Fx are among the elite of manufactures.  Each of these manufactures has different options to choose from and require different shock setups.  Some of the top shock manufactures are Custom Axis, PEP, Elka and Fox.  These manufactures work hand in hand to create shocks that are setup to work with each suspension manufacture.   All you have to do is provide your machine make and model, rider weight, and riding style and they can build a shock specifically for you.