i have the greddy kit on my 2000 si im pleased with it and get good power out of it it's also very reliable, but if you looking for max whp gain than you want the drag kit. but remember with the drag kit you will need bigger injectors and some type of engine management that doesn't come with the kit. on the greddy you will need to buy an intercooler and bov that doenst come with the kit. The greddy adds about 70-80 whp with the intercooler at 7.5 psi and the drag kit adds around 100.