The Top Tech series is finely upgraded as it is. Its got heavier wiring (lipi ready 7.4 only) comes stock with a 6.03 tbb, m 115-120 spring, the famous G&G green bucking, steel gears and bearings. Its meant to be a cqb gun not a field rifle. I wouldnt upgrade the spring as the housing that surrounds the G&G gear boxs are the weakest of all the guns ive seen and break easily with more force knocking back and fourth. Bigger spring = broken gearbox housing. Keep it a cqb gun. It fuctions amazing just as it is
