For the latest G wagon model, what is the difference between the G550 4.0 liter twin turbo versus the G63 4.0 liter twin turbo?
The MB site says the G550 V8 has 10.5:1 compression vs the G63 V8 has 8.6:1 compression. I understand the G63 V8 is hand assembled.
Can someone factually explain what specifically is done to the G63 for the extra horsepower? Is it an ECU tune? Different bore and stroke? Larger turbos? Different fuel injection?
Wikipedia and manufacturer websites are vague about the differences, and I want to understand where the extra HP and torque come from.

 

The engine internals are different. Pistons, rods, crank. Different intake and exhaust manifolds, different turbos, exhaust, ECU tuning. Basically the only thing the 2 engines have in common is the block.

 

Typically there is probably quite a few differences in the internals. Lower compression ratio is one of them, usually due to a combustion chamber being a tad bit larger. Likely due to a different piston shape, or cylinder head shape where the valves sit. But the lower compression itself is not a power producing element usually. The increase in power comes from more air and fuel being pushed into the combustion chamber via more turbo boost, and tuning to keep it from blowing itself up. The lower compression helps from detonation with higher boost.

Both are 4.0L TT V8s, but if you were to take the motors with no turbos on them, the power differences would be negligible. So the majority of the power comes from more boost, more fuel, more air.

I know this may see like an elementary answer, however, thats the majority of it. The turbos themselves, and the engine it self don't necessarily create more power, larger turbos may have been necessary to reliably produce the 577 hp, but larger turbos alone wont create and extra 161 HP. Couple that with more free flowing exhaust, maybe better intake flow, may create a little. Like 20-50 HP (maybe higher rev limit?).

The large majority of the power bump comes from tuning and boost. The rest of the differences are usually needed to handle the extra boost reliably.

 

63 has higher bmep from higher boost pressure (larger turbos, more fuel into the chamber).