So i have been trying to fix my cars for a few days now, i came across something called NetworkOwnerShip. I tried using it for my cars but it made no difference 
This is what i did the first time:
I tried learning more about it and saw some people saying i had to make the car controls on the client (motor speed and stuff) won’t that make a huge vulnerability and make exploiters be able to give the car insane speeds?
I hope someone can help me fix this issue! 
I didn’t quite understand your issue.
It’s a best practice to set the car’s network ownership to the client because it eliminates the input delays.
You can always add server-side checks using the speed formula to check if the car is compromised and is moving at insane speeds.
Alright so i moved the controls to the local script which seems to fix the problem of input delay but the only problem now is that exploiters can change the maxspeed to something like 1000 and fly off into space.
I have no clue of how to safely tell the server the speed of the car without the exploiter being able to stop that process of telling the server the current client sided speed.
I tried using NetworkOwnerShip but it did not seem to work 
Great! Coming to exploit protection.
You are checking the position of the car every X amount of time. And calculate the distance between point A from point B. And then you are going to calculate the speed on server side. And stop the exploit.
This way the exploiter Cannot stop the server.