Tommy Cookers wrote: ↑07 Aug 2017, 10:48
don't we need far more than 40 kW to drive the compressor (eg electrically) for 4 bar MAP ? even with the trickle of blowdown power making a mechanical contribution to said driving but a small reduction in MAP will give a big reduction in the compressor power required and the blowdown power's contribution will significantly increase if the cooling rate is not increased and there's no internal distress in this brief excursion from race condition the ICE power won't fall so the PU power and the amount of K motoring will be maximised
Compressor power at PR=4 is about 100 kW.
I believe they would run the highest MAP possible during "balls out" operation. Running an extra 1 bar MAP will cost some electrical energy, but the ICE output will increase by approximately 1 bar BMEP (pumping gain with zero exhaust back pressure) so a decent chunk of that electrical energy gets to the rear wheels. This is a de-facto method for getting ES energy to back wheels to get around the MGUK limits of 120 kW and 2 MJ/lap.
Interesting note. This "air-motor" technique loses efficiency as intercooling is increased.
Edited to acknowledge TC's allowance of 2% ICE power gain from "forward pressure" - sounds about right for 1 bar MAP increase. I don't think electrical energy is all that precious in a qualy lap - the potential for "hot blown" MGUH harvesting is quite large and they can only use 2 MJ/lap in the K.