It's alot of lightweight actions but really it's the sum of the parts that gets the weight out. The engine itself is certainly a big chunk but other things contribute such as no LTR, no SC pump, no coolant lines front to rear for the SC, No HVAC, no wipers, no air bags, no RCM, no stereo or speakers, no amp, no subwoofer, , no NVH materials, minimal heat shielding, no mastic, no catalysts in the exhaust, lightweight flowmaster mufflers, polycarbonate rear clamshell and bulkhead windows, no AC compressor, no condenser or lines, no accelerator cable or metal pedal, no parking brake system or PB calipers, no carbon cannister, etc etc.