Dawn power dissolver is the way to go. I've used several of the other methods for engine cleaning and this is by far the cheapest and easiest way to get the gunk off. Spray it on, wipe or wash it off, and you're done. It doesn't affect the metal, but make sure it doesn't get on any gaskets or O rings.
I buy mine at walmart. Its in a small blue spray bottle.
Go to http://www.dawn-dish.com/en_US/productlocator.do to find who sells it in your area