You will need the ecu(and maybe other modules and wiring) if you want the 3 stage shit to work correctly. I know that when youre at low rpms it runs in lean mode. Meaning that it only runs on 12 valves with a 20:1 air:fuel ratio. Then at some point in the rpms it runs just straight 16 valve, then at high rpms the vtec rocker kicks in. I don't know how that lean burn ish works. I would get a wiring diagram from the EK3(I think thats what it came out of it might be EK4) and see what else is involved. It could just be the ecu, but I know something has to control the extra vtec solenoid and there is no extra clip on the stock harness. If you have the engine harness the head came with, you could see if it comes with any extra clips for it if it has one.