So I\'ve been playing with these a LOT recently and I am pretty confident I got them to be pretty balanced right now, here are my settings for the scramjet only (I made the ramjet similar, but with better thresholds etc. so it is a bit like the stock engines)... // --- standard part parameters --- mass = 1.5 dragModelType = default maximum_drag = 0.001 minimum_drag = 0.001 angularDrag = .1 crashTolerance = 20 maxTemp = 12500 // --- Atmospheric Engine --- // --- Intake Types 0 = Square 1 = Circular (for area calculation) IntakeShape = 1 intakeSize = 2 intakeSuctionPower = .1 maxIntakePower = 2000 // -- Definition of Airflow performance curves. Lower curve is defined by lower threshold to optimal. Longer spread between values defines a subtle curve. Where closer values will have much faster fall off. Upper curve is between optimal and maximum airflows. optimalAirflow = .1 lowerAirflowLimit = 0 upperAirFlowLimit = 50 //-- Stall threshold determines the point (thrust power) at which the engine can no longer sustain function stallThreshold = 500 // How quickly the engine spools up and down (lerp by time) engineAccelerationSpeed = 0.001 engineDecelerationSpeed = 0.0001 intakeResponseSpeed = .001 // Maximum Engine output maximumEnginePower = 1000 maximumExhaustSpeed = 5000 // -- Standard Engine Parameters heatProduction = 2000 fuelConsumption = 1 Essentially it only works above 40,000 and then it rockets you to 2500 m/s slowly over time. Do note that it DOES give you a quick liftoff squirt, but it immediately chokes up. It\'s a bit rough and still unbalanced, but it\'s some progress. I am considering giving it a MUCH bigger intake area so it really gets going only at super high altitudes and chokes up much quicker at lower ones, as well as some more intake response and a much higher stall number (so it only really activates at PEAK thrust). Oh and do note that with ANY atmospheric engine, it WILL consume fuel based on the throttle you give it regardless of whether it is actually producing thrust or not. This is synonymous to the scramjet dumping fuel into the chamber but being wasted since it\'s not being combusted. Again, I had to lift it up all the way to 40km before it took off and at that point, while keeping the plane at a pitch of 0 (parallel to ground), I eventually got its apoapsis up to maybe 120km before the engine shut down. EDIT: It actually goes to about 800km... But I had to fit two turbojets to get it to its operating altitude and if you go up too shallow, it actually falls back down too quickly.