@Snark Found it.  It's "Real Plume".  Examining it's files shows that it switches "ModuleEngine" to "ModuleEngineFX" but does not alter any parameters.   The result is higher thrust, I get higher speeds (and therefore more weather vane effect, by which I mean the fins keep it flying straighter) and sometimes even loose 1 or more of the small fins at the top of the craft on ascent. If I remove only realplume-stock which is what applies the effects to the engines, I get the same fli
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