Shape the master multiplier curve (red). The power and torque lines are the game's defaults, scaled by whatever the master curve is doing at that RPM.
Left axis is the multiplier applied to the default power/torque at that RPM — 100% line = no change. Drag the master curve above 100% to boost, below to cut. Fill in peak power/torque/redline above to see the right-hand axis in real HP / ft·lb and the x-axis in RPM.