Open the image of the car you want to pimp up.
I've used this image of the 'Bentley Continental Gt 2011 White'
Duplicate your Car Layer [Cmd+J].
Cut out the wheels, I've used Elliptical Marquue Tool (M). Just make a rough selection and hit Duplicate [Cmd+J].
Select your Car Layer again and Transform it [Cmd+T]. I've made it thinner by just dragging the center square of the right side to the left. Around 50% of the original Image.
Now Trim your document by going to [Image » Trim...]
I've decided to make my backside of the car longer. Pick the Rectangular Marquue Tool (M) and select the part you want to stretch.
Select your wheels and drag them on the position you want them to have. I've made my back wheel bigger than the front one using Transform [Cmd+T] because it looks badass!
When it's the right size and right position erase the parts you don't want to have. In my example I've erased the parts i don't want just using the Eraser (E) and Refine Edges.
Now I wanted to give some colour to some specific bodyparts. I've selected the parts using Quick Mask Mode (Q).
Just select 'Edit in Quick Mask Mode' and grab your brush (b) and fill in the parts you want to select.
When done, click on the same button 'Edit in Standard Mode' again (Q) and hit [Cmd+Shift+I] to inverse your selection.
With the parts now selected hit [Cmd+J] to duplicate it into a new layer.
Now you can do anything you want with them! I've made my parts blue using Color Balance [Cmd+B]
Now we're getting to the good part. Let's get this car armored with some weapons!
First thing I wanted to do, is find a place where the weapons can stick out.
So I've selected this part with the 'Edit in Standard Mode' again (Q) and duplicate it into a new layer as in Step 5.
This time, duplicate it twice. We do this because 1 part will be used as 'opening' in the car.
Select 1 of the 2 duplicated parts and make it dark using Levels [Cmd+L] or Hue and Saturation [Cmd+U]
When satisfied, select your other duplicated part and move it a bit away using the Move Tool (V) so you can actually see the opening in the car that you've just created.
I've retouched it a bit using the Smudge, Burn (O) and Dodge Tool (O) to remove the dents and make it look more 3D.
I personally found it look kind off silly to see a floating part. So I've added 4 steel bars to make it look like it's holding the part where it is.
Erased some parts at the back where it 'sticks in the car' so it looks like it fades inside.
Now you have room to add some weapons!
The fun part of this is that you can put anything you want on this car.
Like a Flamethrower, Heavy Machine Gun or even a Cotton Candy Machine..
I've decided I will go for a Machine Gun.
Just place the weapon of choice between the shadow 'opening' part and the floating part.
To make it more realistic I've added some shadow to the weapon.
To do so just duplicate your weapon [Cmd+J] and make it black with Hue and Saturation [Cmd+U] and set the lightness to -100.
Move it a bit with the Move Tool (V) and make it a more blurry using 'Gaussian Blur' (Filter » Blur » Gaussian Blur)
1 Machine Gun looks alright. But 2 looks even more badass!
Just duplicate the machine gun layer. Removed the ammo and resized it with Transform [Cmd+T]
Here i've add the shadow once again using the same technique.
Add or edit anything you want to your desire.
This is my final result:
I hope you enjoyed my tutorial. Feedback or Results are more than welcome in the comments!