There is another HPA enginer on the block and it is the SPECTRE HPA engine from Scalar Airsoft and the company shows how to assemble it in this video... "SPECTRE is a new, high performances electropneumatic HPA drop in engine kit. It replaces internal parts inside the gearbox shell of AEG replicas, with Tokyo Marui standard V2/V3 dimensions.

• Powered by electromagnetic actuators instead of MAC valves, SPECTRE is simpler and cheaper than any other existing engine on the market
• Up to 20% more shots on your air tank compared to other engines
• Put your favorite AEG nozzle on your SPECTRE engine and print your own cylinder head for extreme modularity
• Get the same performances and functionnalities as the best engines on the market."