What is the reason why a car cannot reach 4000 RPM in neutral?

[JasmineMarie]

If a car cannot reach 4000 RPM in neutral, it may be due to the use of low-quality fuel or a dirty fuel tank, which can clog the fuel lines. Cleaning the fuel tank and replacing the fuel pump core can resolve the issue. Torque: When a car is traveling at the same speed and encounters the same resistance, in a higher gear (lower gear ratio), the engine must output higher torque to overcome the same resistance. Torque equals displacement multiplied by the engine's average pressure. For the same engine, since the displacement remains unchanged, an increase in torque must result from an increase in the engine's average pressure. Precautions: At low RPM, the mechanical loss of the engine is small, so the energy generated by combustion is also low. Assuming the thermal efficiency remains unchanged, the amount of energy produced by the engine depends on how much fuel is burned. Therefore, it can be concluded that the engine has better fuel economy at low RPM.