Car Exhaust Smoke

1. First open the photo of your car, I used this one:

Click to enlarge

2. Now create a new layer, call it "smoke". With the brush tool (B), choose a small brush (about 3 px) and white or gray color. Make a smoke form, like this:

3. This smoke will look a bit weird, but no worries - we'll change that shortly. Using the smudge tool (R), blur the smoke in a same direction, from the left to right, so it looks like it's leaving the car.

4. Now duplicate the smoke layer. And in the new layer erase all the smoke until only the beginning (in the left) is there.

Put this new layer as "Multiply". Right click on it and go to Blending Options, apply these styles:

5. Now go back to your original smoke layer and add some noise:

6. Your final result:

Click to enlarge