Chris has explained things well, but just to be clear with what happens with these 'Stage 2' maps that an Unlocked ECU can have. As explained above, an engine that has had improvements made to breathing ability etc (Exhaust, Induction, Cams) will require revised Air:Fuel mixes and Ignition Timing applied to them to get the best from the upgrades. The stock, locked Morgan ECU has some ability to adapt to changes in running parameters (to accommodate varying quality of fuel, temperature, humidity, general engine wear) but these have limited boundries as to how far they can adapt. A Stage-2 engine (ie: one that has all 3 elements mentioned upgraded) needs a new base configuration that better suits the fact that the engine can now breath properly (the standard engine is heavily restricted). Not only will this keep the engine working at its best, but the same adaptive process can continue to do its magic but with the revised boundary parameters that it needs. That's all well and good.
Both G56 and KH will know what map is needed for the typical Stage-2 engine setup and will supply an Unlocked ECU containing that map, running paramters and ability to adapt. Think of this as a 90-95% perfect solution. Most Stage-2 engines perform the same so a G56/KH Stage-2 ECU will do a perfectly acceptable job. If however you want to maximise the benefit of your hard-earned upgrades, then you can elect to have the now Unlocked ECU setup to PRECISELY match your specific engine and environmental conditions. A qualified and experienced Dyno operator will be able to put YOUR engine under differing loads and adjust the 3D Fuel/timing maps to suit that specific engine. The result is that you then have an ECU setup that 100% matches your engine, rather than 90-95% hit. Will you notice the difference? If you're into your engine setups big time, then yes, but plenty wouldn't notice the difference for what might be a £200-300 dyno and setup session. Are you missing out if you get your Stage-2 ECU by post and simply plug ity in? Err, no, not much in all likelihod.
Hopefully that makes sense for those comtemplating Stage-2 ECU-ness in distant lands and without access to the experience and ability of a local S&S specialist with a dyno that fits a tricycle.
