Both nitrous and fuel is introduced in the rubber intake bellow about 3 inches from the throttle body. A few tips for anyone who is interested, install a capacitive discharge ignition (MSD 6A) to burn the extra fuel, install an RPM window switch so nitrous and fuel is only introduced between a specific RPM range (3000rpm - 6500rpm below and above these could mean an engine rebuild) and a bottle warmer to keep bottle pressure within 900psi - 950psi (jettings are calibrated using this value) for those of us in the colder states. Email me for more details.