it takes a GSR p72 ecu and a GSR manifold to get the duel stage vtec. the first one you hear is your vtec oil pressure switch the second sound you hear is the butterflies opening up on the inside of the manifold witch gives more air and with more air more power and sound if you dont have this manifold you dont get duel stage i switched to a skunk2 and it made more power and vtec hit loud and hard 4800 rpms