I'm a new KSPI user, and so I am stupid about these things. I was recently surprised to see that my 3.75m Thermal Engine was also maxing at 2997.1 Isp . I expected it to be either: 2582, because the tooltip for the thermal engine suggests it will be 17 * SQRT(Core Temperature), and the Core Temp of my 3.75M fusion reactor is 23078. 17*Sqrt(23078)=2582 6825, because the LSPI wiki page for the thermal engine says this is the Isp when used with a 3.75M fusion reactor in a D/T cycle How does this really work? Is 2997.1 a buggy result, or the expected result? If expected, can you help me understand why/how this is correct and how I can predict Isp and thrust for the engine?