simple car controle

am using one script for my car movement. that was downloaded from Internet. in that i can't increase the speed to my vehicles. this is my script

using UnityEngine; using UnityEngine.UI; using System.Collections;

public class CarController : MonoBehaviour {

 public float idealRPM = 500f;
 public float maxRPM = 1000f;

 public Transform centerOfGravity;

 public WheelCollider wheelFR;
 public WheelCollider wheelFL;
 public WheelCollider wheelRR;
 public WheelCollider wheelRL;

 public float turnRadius = 6f;
 public float torque = 25f;
 public float brakeTorque = 100f;

 public float AntiRoll = 20000.0f;

 public enum DriveMode { Front, Rear, All };
 public DriveMode driveMode = DriveMode.Rear;

 public Text speedText;
 Rigidbody body;

 void Start() {
     body = GetComponent<Rigidbody> ();
     body.centerOfMass = centerOfGravity.localPosition;
 }

 public float Speed() {
     return  wheelRR.radius * Mathf.PI * wheelRR.rpm * 60f / 1000f;
 }

 public float Rpm() {
     return wheelRL.rpm;
 }

 void FixedUpdate () {

     if(speedText!=null)
         speedText.text = "Speed: " + Speed().ToString("f0") + " km/h";

     //Debug.Log ("Speed: " + (wheelRR.radius * Mathf.PI * wheelRR.rpm * 60f / 1000f) + "km/h    RPM: " + wheelRL.rpm);

     float scaledTorque = Input.GetAxis("Vertical") *torque;

     if(wheelRL.rpm < idealRPM)
         scaledTorque = Mathf.Lerp(scaledTorque/10f, scaledTorque, wheelRL.rpm / idealRPM );
     else 
         scaledTorque = Mathf.Lerp(scaledTorque, 0,  (wheelRL.rpm-idealRPM) / (maxRPM-idealRPM) );

     DoRollBar(wheelFR, wheelFL);
     DoRollBar(wheelRR, wheelRL);

     wheelFR.steerAngle = Input.GetAxis("Horizontal") * turnRadius;
     wheelFL.steerAngle = Input.GetAxis("Horizontal") * turnRadius;

     wheelFR.motorTorque = driveMode==DriveMode.Rear  ? 0 : scaledTorque;
     wheelFL.motorTorque = driveMode==DriveMode.Rear  ? 0 : scaledTorque;
     wheelRR.motorTorque = driveMode==DriveMode.Front ? 0 : scaledTorque;
     wheelRL.motorTorque = driveMode==DriveMode.Front ? 0 : scaledTorque;

     if(Input.GetButton("Fire1")) {
         wheelFR.brakeTorque = brakeTorque;
         wheelFL.brakeTorque = brakeTorque;
         wheelRR.brakeTorque = brakeTorque;
         wheelRL.brakeTorque = brakeTorque;
     }
     else {
         wheelFR.brakeTorque = 0;
         wheelFL.brakeTorque = 0;
         wheelRR.brakeTorque = 0;
         wheelRL.brakeTorque = 0;
     }
 }


 void DoRollBar(WheelCollider WheelL, WheelCollider WheelR) {
     WheelHit hit;
     float travelL = 1.0f;
     float travelR = 1.0f;
     
     bool groundedL = WheelL.GetGroundHit(out hit);
     if (groundedL)
         travelL = (-WheelL.transform.InverseTransformPoint(hit.point).y - WheelL.radius) / WheelL.suspensionDistance;
     
     bool groundedR = WheelR.GetGroundHit(out hit);
     if (groundedR)
         travelR = (-WheelR.transform.InverseTransformPoint(hit.point).y - WheelR.radius) / WheelR.suspensionDistance;
     
     float antiRollForce = (travelL - travelR) * AntiRoll;
     
     if (groundedL)
         body.AddForceAtPosition(WheelL.transform.up * -antiRollForce,
                                      WheelL.transform.position); 
     if (groundedR)
         body.AddForceAtPosition(WheelR.transform.up * antiRollForce,
                                      WheelR.transform.position); 
 }

}

check it.... help me