Did you get this working? I tried Both of these and both do not work.. any tips? @PART[RAPIER]:Final { @MODULE[ModuleEnginesFX,AirBreathing] { @maxThrust = 210 } @MODULE[ModuleEnginesFX,ClosedCycle] { @maxThrust = 195 } } and @PART[RAPIER]:Final { @MODULE[ModuleEnginesFX]:HAS[#engineID[AirBreathing]] { @maxThrust = 210 } @MODULE[ModuleEnginesFX]:HAS[#engineID[ClosedCycle]] { @maxThrust = 195 } } Tried this and it does work thought if anything adds another "MODULE" to the Rapier I think it may break it. @PART[RAPIER]:Final { @description = NabbTech Certified! The R.A.P.I.E.R. (Reactive Alternate-Propellant Intelligent Engine for Rockets) is a joint venture between C7 Aerospace and the Rockomax Conglomerate. Designed to fill a gap in the design requirements for sustainable single stage to orbit aircraft, this engine combines the best of rocket and air-breathing thrust technology. @mass = 1.80 // attachment rules: stack, srfAttach, allowStack, allowSrfAttach, allowCollision @attachRules = 1,1,1,1,0 //!MODULE[ModuleEnginesFX] {} @MODULE,2 { @maxThrust = 210 } @MODULE,1 { @maxThrust = 195 } }