Do I remember that with the original Thielert 135, a converted PA28-161 compared to a Lycoming powered one:
1. Weighed 160lb more?
2. Climbed at a reduced rate to 2000ft?
3. Cruised 5 kts slower?
Add to the above the cost of overhauling the CS prop (note poorer performance despite the CS prop) and the sparse maintenance cover over a standard aircraft.