To decide if you need an inj.module is essential know what is it and how it work: on fz1 like on others bikes,the factory need a compromise between the respect of pollutions restrictions and the best engine's expression possible so the electronic injection's ecu is made to work with a catalyzer. When you change the exoust terminal,differently from other bikes(new z1000 for example),you loose the catalyzer and the exoust valve. In this situation(stock bike with after market terminal only),you can experiment differents sensations that are different from a fz1 owner to another 'cause every fz1 is different from another and the number of ex.term today is infinited..Is important understand this thing: 2hp ex.term,more 1hp with air filter and 6hp total with inj.module is NOT THE TRUE! The inj.module is necessary to optimize the work of stock module that you can't modify..loosing the catalyzer you are free from pollution restrictions so is normal looking to a performances improving but a lot of owners never find it!!PowerC like a rapidB or a bazzaz(but to optimize engine work with an after market ex.term there are cheapers solutions)consent you bypassing the stock module to work on inj e anticipo(I don't know english word)cylinder by cylinder free one from another. Another essential point is that if you want a good job,the map need to be created on a dyno board..the preinstalled maps are not dedicated to your bike so is very probably have a bike with ex.term and inj.module with a dirty engine expression..With sport air filter the bike breath better so the perfect team(inj.module+ex.term+airfilter)is ready to launch the bike on dyno board to create a perfect customap that give a better torque's curve with pic torque on lower rpm zone(!!!),improve max power but you'll find more hp on every rpm regimes and,incredible but true,the bike use less gasoline!! Inj.modules really consent you to make upgrades step by step..a shiftgear for example and(dimsport will present the new module for rapidbike at eicma 2011,I know for sure)traction/weeling control!Anyway I hope that I had explane how much important is understand what change on the bike with a part changing to have no delusions and to dont loose money..