Wheel axles were vertical in Unreal (the FBX armature conversion rolled them 90 deg
about X). Fix: axis_forward:X in the character preset and a Blender-Z wheel tail so the
axle lands on Unreal Y. This is correct (reference pose FL roll 180 / FR roll 0) but
does not fix the reverse: -drivetest still -2737 cm/s, and FinalRatio sign is a no-op.
The remaining cause is the Chaos wheel spin-axis convention or engine torque sign.