Problems with C18 engine
1. 1250 hours on turbine overhaul
2. Above about 25 degrees C the engine will TOT out before torquing out
3. More expensive to overhaul, parts havent been made for years
Advantages
1. No cycle count
2. about 15 to 18 gals an hour
The C20 engine in a c model is the hot and high version of the 369HS (C18). Basically all 4 bladed models have a max transmission limit of 275 shp of which both engines give at 15 degrees. Hence stick a c20 in and she will take off at higher temps as she doesnt tot out
High skids will slow you down a bit and you will have to pay about $ 20k as you have to change the dampers as well as legs and skid tubes !
The C20B engine was used in the D and E models as the transmission went to 350 cont and 375 for take off ( C20b about 420shp)
Hope this helps