Yeah its mainly a marketing ploy for the company's products, but typically Stage 1 is just EM (mainly Cobb users) and Stage 2 is EM and turboback. Stage 4 is a bigger turbo and supporting mods. Then theres wierd ones like Cobb Stage 2.5 adds a VF34. Its confusing. Especially since I dont know and havent ever heard anyone talk about "stage 3", so why is there a stage 4?