I would agree that its a MJ issue, except that MJ agrees with the thrust listed in part.cfg, but when actually on the runway (not the editor) the engines only produce half! I.e., the engine claims 120kN, mechjeb uses that to estimate from the vessel mass, a TWR of, say, 1.5, and once I click "launch" I see the engine maxing out (full throttle) at 60kN, and needless to say don't take off with .75 for TWR... So something seems to be causing the engine (all 3 of them) to put out half the thrust... Last I checked I had only MJ and the engines, no other mods. I will try testing it again though, and maybe check to see what version of Pitch Vector engines I have. Though like I said before, I'm guessing its the last one... Anyway, while I could arbitrarily double the thrusts of my engines, so they would go to normal, I am pretty sure MJ would still be screwed up, making it hard to balance mixed-engine vessels... And, while this is quite a silly reason for sure, not being able to use these epic engines (correctly anyway) has basically kept me from playing kerbal for the last month or so. Dumb reason, I know, but I really like those engines, and using them in conjunction with other engines in forward flight (out of vtol), which is a pain to compute when the engines put out 1/2 thrust in flight but MJ reports full in editor (I've been doing that since thrust limiting became a thing in the editor, so you could turn some engines off and check balance). If only I knew enough to fix it I would totally try. I Will work up the patience to test it again, and post results, maybe the problem vanished as magically as it appeared (can only hope)... PS: Can I post images (screenshots) here? Would screenshots of the problem help?