I have a sick bike parts expansion pipe on my bike. I put a long header on it and it's great for increasing the low end torque. However, some of the dirt bike pipes are far superior for these engines. I wish I knew about them before I got mine. These dirt bikes pipes are awesome for these engines (KX65, KX80, RM80, CR80, KTM65). They are more expensive than the sick bike parts pocket bike pipe but I've seen bikes with them and they are far superior. However, if you don't want to spend the money, the sick bike parts one will give you a noticeable increase in performance.