How to increase acceleration

how can i increase my customvehicle acceleration?

Use UWheeledVehicleMovementComponent (blueprint version should have also name like that) on your actor, which gives you physics for vehicile, acceleration will be inhirite from UMovmentComponent… but you might find better way to move a car in wheeled vehicle movement component:

https://docs.unrealengine.com/latest/INT/API/Runtime/Engine/Vehicles/UWheeledVehicleMovementComponent/index.html