Introduction
I don't know what the deal is with Carbon Fibre Hoods. They may look cool to some people, but to me it looks like you were to cheapy to buy a matching hood. But that's just personal. From my professional Photoshop-point of view, it's a very cool technique, very easily done.

The pattern
Find yourself a picture of a car. Obviously one where the hood is visible. I chose the gorgeous Chrysler 300C, one of the VERY few cars I know the full name of besides just the brand or "That car with the wheels like that.."

For the Carbon Fibre-pattern, let this document stay here and go to File>New and create a document with the dimensions 4px by 4px. Using 4 shades of Grey, repeat this pattern shown below. I also got the color-codes!

Using this very simple pattern of 4x4, fill this up using the Pencil-Tool (B). When you're done, go to Edit>Define Pattern and save this pattern as Carbon Fibre, or anything you like. Now, close this and hop on back to our car. Create a new layer and grab your Rectangular Marquee-Tool and draw a random rectangle. with the selection still active go to Edit>Fill and choose the pattern that you saved. This will fill the selection with your carbon fibre-pattern.

Applying it to the car
Go to Edit>Transform>Distort and drag the corner anchorpoints so that it matches the hood of your car. If you're using the same stock as me, check the image below to see how I placed them. This is basically just clicking them and dragging them to the designated area. Press OK when you think you have the perfect distortion.

Now, because this rectangle is way too big for the car, grab the Pen-Tool (P) and cut off all the unwanted carbon fibre. I only made it so the hood is fully covered. Press CTRL+J to duplicate the carbon fibre-layer and set the original to the blending-mode COLOR. Set the duplicate to MULTIPLY and you're done!

Conclusion
Now the car looks a lot better... to some people. Still, you can really place this on any part of the car. And not just on cars, but with Photoshop, you can even pimp bicycles, humans and animals. If you don't like the carbon fibre-pattern, I say go experiment with other fancy patterns. You know the drill now!