I always felt the Manor in this game felt a little bit... Generic.
after a bit of fiddling with it however, I've made the car have lower aerodynamic abilities - reducing its handling somewhat but making it top speedtraps like a drag racer.
The top speed when tested in time trial at monza was 236mph.
I know this isnt entirely realistic, but its better than the rather generic backmarker stats we had previously.
And yes, this mod changes car performance. Therefore you cannot use it in multiplayer.
For those who want to see the new car performance, i'll upload a youtube video demonstrating it soon. not much but hey.