I lapped the one I borrowed (hollow type), but I did not do a "before" measurement. Sorry. Running a Tbird at 80W, using the 26cfm YS-Tech Fan (from my FOP-32), it delivered .30c/w. That was using a type T thermocouple in the base of the ThermoEngine, resting on top of the core. I would expect it to do better with a faster 60mm fan, or an adapted 80mm fan.