Scripting a quickboost

Unity Engine
1

Hello, I followed a tutorial about making a jetpack:

using UnityEngine;
using System.Collections;

public class Jetpack : MonoBehaviour {
float fuel=5, maxFuel=5;
CharacterMotor cm;
CharacterController cc;
bool isFlying;

Rect fuelRect;
Texture2D fuelTexture;

// Use this for initialization
void Start () {
cm = gameObject.GetComponent<CharacterMotor> ();
cc = gameObject.GetComponent<CharacterController> ();

fuelRect = new Rect (Screen.width / 10, Screen.height * 9 / 10,
Screen.width / 3, Screen.height / 50);
fuelRect.y -= fuelRect.height;

fuelTexture = new Texture2D (1, 1);
fuelTexture.SetPixel (0, 0, Color.red);
fuelTexture.Apply ();
}


// Update is called once per frame
void Update () {
if (Input.GetKeyDown (KeyCode.LeftControl))
isFlying = (true);
if (Input.GetKeyUp (KeyCode.LeftControl))
isFlying = (false);

if (isFlying) {
fuel -= Time.deltaTime;
if (fuel < 0)
{
fuel = 0;
isFlying = (false);
}

cm.SetVelocity(new Vector3(cc.velocity.x,10,cc.velocity.z));

}
else if (fuel < maxFuel)
{
fuel += Time.deltaTime;
}

}

void OnGUI()
{
float ratio = fuel / maxFuel;
float rectWidth = ratio * Screen.width / 3;
fuelRect.width = rectWidth;
GUI.DrawTexture (fuelRect, fuelTexture);
}

}

But now, what I want, is to make a script who will add some powers, its like a boost in front, and at sides, it should mulitply the jetpack speed by 4, and the boost works only for 0.5seconds, somethings like that
If you know the game armored core 4, it’s like that! And the boost should use the energy used by the jetpack, but it will cost more
How can i script that? I’m a beginner
(sorry for the bad english)

2

UP please!