The Porsche PFM never really sold as only 41 units were built so I guess it must be considered a commercial failure. I think there was a lot of entrenched thinking in traditional aviation circles as this was a difficult market to break into for Porsche, and I believe Porsche headed up by Peter Schutz grossly underestimated this particular task.
Previously VW flat four cylinder “Beetle” car engines had been adopted for aircraft use, mainly in the “homebuilt” arena and the fact that these need a reduction gearbox and were in fact labelled a converted car engine, did not help Porsche move into this market.
My knowledge of Porsche over my life would lead me to think that the PFM was virtually a completely new engine and I doubt if many stock car parts if any were used in it. Perception is everything when marketing a new product. The Porsche PFM was labelled by aviation analysts as, “too complicated.” This was mainly due to the fact that it had a reduction gearbox and associated moving parts that could all go wrong. Porsche had also retained the main air-cooling fan, which competitor engines do not have fitted, which relied solely on the propeller to cool the engine. Also regular aviation piston engines turn at around 2,500 rpm as a maximum, and are usually very large capacity and slow revving, so taking a relatively small capacity engine that was designed to turn at twice the accepted revolutions, was also a perception problem and hard to overcome.
If I ever get the funding organised, I would love to build my own aircraft and I would not shrink from installing a PFM(s) in it, no matter what the economics or perception was at that time. One of my future projects is to build a replica Supermarine Spitfire or ideally a twin engine WW11 Mosquito, the Porsche PFM would be the power plant of choice for me irrespective of what others may say, assuming I can get hold of a couple.
I was one of the few pilots to have experienced this engine and it had so many benefits and Michael and Hans had proved it beyond doubt with their “Round the World” marathon!