There is no doubt in my mind that all the F1 PU's are utilising blowdown energy as well as pressure energy.
Blowdown energy is "free" in that it can be utilised without increasing backpressure on the engine. Blowdown energy is contained in a brief high pressure, high velocity pulse ejected from the cylinder when the exhasut valve opens and the cylinder pressure is still much higher than the exhaust manifold pressure. To harness this energy, the pressure pulse must be piped to the turbine without adding pressure to the exhaust of any cylinder that is executing its exhaust stroke. If that happened, the pumping work of that cylinder would be increased by the higher back pressure. To ensure this happens, each exhaust header must service a maximum of three cylinders and those cylinders must be evenly spaced in the firing order. The headers must then be kept seperate all the way to the turbine and the turbine must be designed so the blowdown pulses from one header cannot communicate with another header. One look at any of the F1 PUs shows that they are all utilising blowdown energy (including Merc). The clue is the turbine itself having two seperate entries with three cylinders plumbed to each entry.
In addition to blowdown energy, the turbine can extract additional energy (pressure energy) if the pressure in the header is higher than atmospheric during the "non-blowdown" period. This will require the pistons to work harder during the exhaust stroke - robbing the recip' of some power. This lost power will however be less than the power gained from compressed intake air pushing the pistons down during the intake stroke (MAP will be greater than BP in a F1 engine). I believe F1 PUs are using pressure energy in addition to blowdown energy for the following reasons.
1. The airflow required to achieve the most efficient AFR cannot be flowed by the 1.6 litre engine without significant boost pressure. This boost pressure cannot be generated using the turbine power generated by blowdown alone - especially if some turbine power is to be harvested in the MGUK.
2. The most efficient combination of expansion in the cylinder followed by expansion in the turbine occurs at a significant turbine pressure ratio combined with a moderate recip' compression ratio - probably between 9:1 and 12:1. I explained this in more detail here http://www.f1technical.net/forum/viewto ... 73#p536873