Compaign speed bug

Hello fellow autiomationers, im new so apologizes if this isnt the right place to ask.
I bought the game some months ago and started a campaign but i didnt gave it so much time for work-related small time that i have.
My company was an archana-based cheap themed one so now im starting to do sport and fast cars (2006)
The problem is my first v8 car. No matter what hp it has (280, 320, 430, 580) it doesnt reach more y than 140mph/226kmh having a 3.5s 0-60, a theorical speed of 370kmh and a final one of 340. I use max quality components and cheaper ones, same result.
With and without downforce
For example, i have a premium sedan with a 260hp v6 and does the same speed
The thing is that it reaches that speed and dies way ahead the 8200rpm limit, in 6 th, in 5th and even 4th gear.
The problem and the bug is that doing the same car in the sándbox mod works, it goes 300kmh. Only in campaign. I started a new one for testing doing the same and it happened again. It seems that no matter what i can only modify the time that the car needs to reach 140. I cant pass that speed. Thanks