There is one, not that small, difference between R-3350 and road car turbocharger - size. Tip clearances are not scaling down linearly, and they are big source of losses in efficiency.WhiteBlue wrote:Have a look at the famous Wright_R-3350 aero engine with single stage axial turbines used for turbo compounding. That application is now 65 years old and it probably was the commercially most successful application of turbo compounding ever done to piston engines. F1 will not be too far behind 1945 technology when they start their own lead application. This is why I'm confident that the F1 designers will at least look at axial turbines for efficiency reasons. If you set your objectives too low you will not be successful.
And there is also problem with finding matching compressor, within the rules defined by FIA, which were set to prohibit already existing technologies.
However, to be clear, I have no doubts axial turbine will be (or rather was/is) taken into consideration. I just do not see it as the preferred way to go, but that's just my opinion.
As for sub-system efficiencies used in estimation(s). You can have compressor with peak efficiency ~80%, MGU having 96-97%. Overall I think 90-100kW is what can be expected as max compounding power in 2014.