Interesting, but I don’t think it was intended to be analysed down to the pixel level. It really only needs to be accurate to grid level.
On your engine graph, it goes to 10,000 RPM separated by 10 grid lines. This means that each section, grid line to grid line, is worth 1,000 RPM. The engine output figures stop right before 8,000 RPM - it would seem somewhere around 7,800. This means that the engine can be run as high as 7,800 RPM and it will still produce power and torque. The engine will not physically rev any higher.
On the gearing graph, it goes to 8,000 RPM and is again separated by a 1,000 RPM grid line to grid line breakdown. The redline is right above 6,000 RPM which means that is the indicated redline and you should probably shift into the next higher gear. Anything above that RPM the engine may not be receiving fuel and may cause damage to the motor.
On way to try this would be to turn on Simulation damage and run the car with manual or manual with clutch shifting. Run the car down a straight road with little traffic and shift right at the Gearing Graph indicated RPM. See how it works. Record any data and damage. Next, fix the car up and this time, run the same test but let the motor rev as high as the Engine Graph shows it can before shifting. Again, record data and damage and compare results.
I don’t necessarily think it is a glitch or an error - the two graphs are simply indicating two different measurements. Also (in best Bill Nye impression) CONSIDER THE FOLLOWING: The engine graph is a picture of torque and horsepower outputs that the engine is capable of producing. I can record those figures without a car by simply running the engine by itself and measuring output. The gearing graph shows gear spacing and a redline that is lower, and limited, because it depends on the transmission in the car. Depending on the transmission itself, the car as a whole may not be able to produce the data indicated by the engine graph even though the engine on it’s own could. The gearing graph is considering the same data from the viewpoint of the transmission. Also, jut because the engine is capable of spinning that fast and producing those output figures does not mean it is viable in application.
Think of it almost like a 0 - 60 acceleration times. They’re nice, but really - for FH2 purposes (outside of drag racing) - who cares. It’s not a helpful figure. Basically, any data between the gearing graph redline and the engine graph redline isn’t practical and you shouldn’t spend too much time worrying about it during your build. The important parts are between idle RPM and gearing graph indicated red line.
I hope that makes sense.