My 24 year old plane with inefficient wings and low tech, gas guzzling IO540 engine is more fuel efficient than a VW Golf TDI 1.4 at high speed. The Golf has about the same curb as my airplane. At very high speed drag becomes the overriding factor for fuel efficiency. In other words a fair comparison.
My airplanes consumes about 14 mpg at 170 mph, at 2500 feet altitude where the effects of lower drag due to thinner air are insignificant.
The Porsche Cayenne Turbo S at 168 mph has a fuel flow of 3.5 mpg.
The other thing is that at the high speeds, the car ECU throws away most of “engine management” and just feeds the fuel in as fast as it can pump it, well ROP, whereas your TB20 can be doing that speed at peak EGT.
The only thing which beats an IO540 running at peak EGT is an engine with a much higher compression ratio – a diesel.
Watching the fuel:air ratio in real time on my 2000 vintage ECU it doesn’t seem to go anywhere near well ROP, regardless of load.
