I use a mixture of Simply Green and water. 10 parts water and 1 part Simply Green mixed in a spray bottle. Get the engine warm (NOT hot, warm - means turn a COLD engine on for no more than 3-5 mins. The warmth loosens up the grease.
Cover any electrical components (alternator, fuse box, etc) with plastic bags (as needed, I don't personally do this on my cars, but to each his own-I take no responsibility) spray down the engine with the SG/H20 mixture. Use a brush ( I like to use a heavy bristle brush and a few old toothbrushes-I usually go thru 2 or 3 toothbrushes, as they will get gunked with grease) I also have a spray bottle with just plain water that I rinse the engine with afterwards.
Continue this process until it's clean as a whistle.
here are some samples of this tecchnique that I've done.
Note: If the motor is very dirty (like the WRX motor pictured below, I sprayed an old terry cloth towel with full strenght Simply Green and prewiped alot of the grease off then did the above tecnhinque. If it's still too greasy, spray with full strenght SG instead of the 1:10 SG:H2O.)
WRX before (not my old one, a friend of mines)
Member Keith McVey's car before
I had an amazing before/after from my old Integra, but it's not on my site anymore. . .
gunk is much more powerful than simple green. i just pulled my motor out and completely cleaned it w/gunk. the one i used had an orange top. works awesome but make sure you get it all off or it will start to eat away. i dont think you are supposed to used it on aluminum. be careful
Just a FYI, Simple Green will stain aluminum if used too strong or if left on too long. I use Orange Blast for my cleaner. I use CD2 Engine Detailer, an acrylic base product, for protection and shine since it is non-oily and dries hard.