The premise behind engine block cooking is that you use the heat of the engine to cook food. This means that the engine must be hot, so you'll need to keep the car running the entire time the food is cooking. The speed you're driving while your food's on the engine doesn't matter that much. But many car cooking recipes call for dishes to be cooked for a certain number of miles (kilometers) rather than a certain amount of time. So if you hit traffic or you're driving a curving, one lane road, your food may be done before you've driven as far as the recipe calls for.
The first step in car cooking is to prepare the uncooked food. Lay the food on a piece of foil. Bring the two opposite sides of the foil up to meet in the middle and fold over several times. Then bring the other two sides up to the top of the package, and again fold the foil over several times. You should have a very neat, well-sealed package. Now repeat that process again with a second sheet of aluminum foil. Use at least two layers of foil to prepare your food package -- three is even better.
Now you're ready to set the package on your engine. It helps to know what part of the engine produces the most heat. Any plastic area on your car's engine won't get hot enough for cooking. You need to stick with the metal areas. The exhaust manifold is usually a good choice, assuming you can easily access it. To determine what other areas make good cooking spots, take your car for a spin around the block. When you get back in your driveway, turn off the engine and pop the hood. Quickly touch any flat metal areas of the engine to see how hot they are. Or, if you're afraid you'll burn your finger, drizzle a few drops of water on different areas of the engine. If the water jumps and sizzles, the area is hot enough for cooking.
You have your meal packaged and you've decided where to place it on the engine. But how do you make sure you don't lose your dinner on the highway?