Ramjets losing thrust

[V1rtua1An0ma1y]

I've seen videos of ramjets getting up to 250kn of thrust around 25km and these crafts are able to go over 2km/s in the atmosphere. Every time I try this, the engines peak around 210kn and then start losing thrust. I'm stacked with intakes and the intakeair resource is even above .50 when this starts happening. Can anyone explain the finer points of ramjets?

[rryy]

The ramjets do have a peak thrust of 250 kN at around 18 km, but at higher altitudes, there is less drag, so even if there is less thrust to push the aircraft, there is also less air in the way to slow it down.

[EndlessWaves]

Turbojet thrust is depedant on speed, with maximum thrust happening at 1000m/s, half thrust at 2000m/s and no thrust at 2400m/s.

[Scialytic]

If it got all the way up to 250 kN, I think the video must be from an older version of the game. The part.cfg maxThrust is now 225. As EndlessWaves said, the thrust follows a velocity-dependent curve. Also, the Isp changes based on air pressure.

[V1rtua1An0ma1y]

I think it was just 225kn, then. Either way, the video I saw specifically said 19.1 and was posted just a few weeks ago:

. I do find it odd that in the video the ramjets begin to overheat at the time I would be losing thrust, so I wonder if there's modding involved...