Oct. 6, 2017, 9:52 p.m.
Maximum in-game RPM is (I think) limited to somewhere around 10,000 - 11,000 RPM. The gauge on your HUD during gameplay shows this. Modders usually prefer redline at 8,500 - 9,500 RPM
If you want to make the car accelerate faster, increase the torque. If you want to change the top speed of the car, modify its gear and final gear values. Generally, large gear value allows for higher top speed but slower acceleration although this can be countered by increasing the torque value.
Other values such as drag coefficient, shift speed, tire grips, downforce can also be modified to increase the performance but I suggest be careful editing those.