$20 hour Cessna 172?

[jsstevens]

[snip] But didn’t Porsche make and certify an engine for Cessnas and Pipers back in the 80’s?

Close. It was for a Mooney: https://www.motor1.com/news/431982/mooney-porsche-plane-for-sale/

Although apparently there were many more models in Europe: https://www.porscheaviation.com/

They were not very successful though I think it had little to do with the engine's reliability.

 

[Capt. Geoffrey Thorpe]

but Rotax doesn't seem to have trouble. Do they have some magic,

Radial engines - pretty much all of the moderate to big stuff used gears. Often quite a few cylinders. Less than abysmal results.
The geared Lycomings - still had the big displacement, long stroke, relatively slow redline to beat up the gears. At low power settings the lumpy torque profile could result in a lot of torque reversals at the gear box banging the gears back and forth through the lash.
Rotax - it idles over 2000 rpm. Cruise around 5000-5500 Small cylinders, short stroke, not pounding the snot out of the gears. They also have clutches to ease sudden loads on the gears and limits on prop weights.

 

[AlphaPilotFlyer]

One of the experimental forums has a section just for auto conversions and the $20/hr sounds about right for the HP. There’s a C172 nearby that’s been in a hanger for years after a prop strike just collecting dust and thinking about seeing if they want to sell it.....maybe get a good deal, and put their V8 on it and fly experimental. Their website shows video of a 1969 Skyhawk way out performing a new stock Skyhawk.

I sent them an email about pricing. Their website shows a guy fueling from a car with a 12V pump. I’m not sure my $4.85/gal AVGAS FBO would allow that!