Unleaded avgas AVAILABILITY is one thing. Satisfactory testing and certification on hundreds of GA aircraft/engine combinations (seals, gravity-feed heads, etc.) may be another issue. 2018? Suuurrre. . .

You are comparing apples and oranges.
160HP-180HP? At what speed? Show me one modern car engine (even V12...) which can do 180HP at 2000rpm. They can do that at 5500 or even higher, at that speed the Lycomings can produce 350HP or more (ask the Reno-Guys...)
Going 120 kts (220 km/h) with a modern SUV is barely possible with 18.3 l/100km.

Compare comparable numbers please, but as stated before, SFC numbers for cars are hard to come by. Even l/100km values which are not just possible on special test stands with special tires, no A/C etc. but in real life are hard to come by.

Pistons may have the size of saucers, but look at their actual shape and contact area. It took the car industry up to the late 90s to produce pistons which are not just the shape of a tin can and optimized for cheap production, but optimized for weight, contact area, oil distribution, heat transfer etc. Modern car engines are now further advanced, even with some non-metallic anti friction coating in the highest contact force area, but that is a thing of the last 15 years.

Taking into account the typical speed of propellers, turbo charged direct drive diesels are most probably the way to go, but these machines are real propeller murders. The torque peaks ruin every blade root bearing... So unless we design some Propellers with elastomeric roots (similar to what the helicopter folks do) we will not get very far. Reduction gearboxes have also not proven too reliable yet, so modern high speed turbo charged direct injection petrol engines are also not that easily made.

There is not much doubt that the aera of high octane fuel is over. So somehow we must find a new way to power piston aircraft. Fast.

Maybe the club/flying school business will very soon move into electric aircraft, then the market for high performance long range aircraft will become a real challange, because it will be very, very small. And no market to develop a new engine for.

It certainly seems a pity that we have failed to modernise our light piston engines since WWII and have been running essentially the same dinosaurs since then, virtually unchanged.
This is roughly equivalent to modern cars being powered by the engine from a grey Ferguson tractor on the sole basis that it is reliable and there was "no call" to modernise it.

The white heat of technology went cold in the late '30s as far as light aviation propulsion is concerned, and is only now beginning to warm up again.

If Honda can build utterly unbreakable, utterly reliable, lightweight 150BHP engines for motorbikes it seems a shame they haven't done the same for aircraft.

er...Jaguar XKR for a start. There must be more as the Jag is far from an extreme engine, though blown.

As I've posted previously, the figure of interest in any piston engine is the SFC.

One ex car engine at least has been certified by the FAA, and used the Toyota Lexus V8 as the base. See here if you want a max power of 360HP at 5,200RPM,

http://rgl.faa.gov/Regulatory_and_Gu...E/E00052en.pdf

It quotes a maximum best economy cruise SFC of .382 at 4,400RPM, though how much HP that is is not stated. By comparison Lycoming have engines that will make a SFC of .4 at 75%. Found it interesting that it has a dual channel full authority digital engine control, but only one plug per cylinder.

There is always a downside, the FV4000 was tested in a Malibu and found to be heavy, had some exhaust problems and would have been expensive to manufacture, on the order of $100,000 per unit (2002 dollars).

The factory says that B2N2's DA-42 at 60% power has a SFC of .338 as an example of diesel economy.

To reiterate, the Lycomings etc don't do too bad, given their simplicity.