Engine performance at certain altitudes/speeds

[Kokanee]

Is there any way to make an engine only work at a certain speed/altitude, or at least have horrible performance until say, 300m/s is reached etc? I'm fiddling around with a RAMJET engine and this is the final piece of the pie so to speak... Any ideas are appreciated.. I think I need to alter the velocity or atmosphere curves but have not been able to find documentation on the variables.

[NathanKell]

velocityCurve. Look at jets; they have low thrust under ~300m/s

Actually, just look at how Taverius (the master at this sort of thing) handled ramjets in the TVPP here: http://forum.kerbalspaceprogram.com/threads/15348

velocityCurve: first variable is speed, second is multiplier to thrust, third and fourth are in and out tangents.

atmosphereCurve: first variable is atmospheric pressure in atmospheres (i.e. ranges from 1 to 0), second is Isp, third and fourth are in and out tangents.

[Sethnizzle]

You also might want to check out this Afterburner mod by Osprey Propulsions Technologies.