The final part of this complex LS600h puzzle is the advanced drivetrain. Here at TrustedReviews, we're not in the business of arguing the toss over the merits of V8 engines versus V12s. But the techie nature of this car's hyrbid propulsion does merit an overview. The broad picture starts with a 5.0l petrol V8 cranking out 389bhp. This is supplemented by a 221bhp electric motor built into the combinated gearbox/differential casing. Together, these two power plants make 439bhp available to all four wheels. That's correct, the sum is much less than the parts. However, the shortfall is by design - the idea is that the electric motor supplements both power and efficiency. Using both to the maximum simultaneously would compromise the latter.
Electric power is stored in a 240-cell Ni-MH battery pack capable of 6.5 Ah and charged by both the V8 engine and regenerative braking. Now, we could tell you that the overall result is extremely impressive, delivering weighty, linear acceleration that feels much the same beyond 100mph as it does at 60mph. We could also regale you with the fun and frolics possible when using the drivetrain status monitor in the instrument binnacle to juggle power between the electric and petrol motors. But all of that is really beside the point. What really matters is how well the 600h delivers on its green credentials.
Officially, the 600h returns 30.4mpg on the combined cycle and is rated at 219g/km in terms of carbon emissions. That compares with 25.4mpg and 261g/km for its purely petrol-powered sibling, the LS460. During our time with the LS, it returned averages in the mid 20s, no doubt thanks to what we might euphemistically describe as enthusiastic driving. Still, that's a pretty impressive achievement given that the LS460 sports a smaller, less powerful 4.6l V8.
It must be said that the system is also extremely well integrated. Virtually zero driveline shunt is detectable as the petrol engine cuts in and out during stop start traffic. Our only significant criticism of this specific hybrid implementation is that the Ni-MH battery runs out of juice rather rapidly in heavy traffic. While we cannot be entirely sure, we suspect this may eventually have an impact on fuel efficiency.