If your engine is particularly bad you'll need a pressure cleaner handy but you can't go past using non caustic oven cleaner (you have to make sure it is non caustic or it'll eat paint, rubber and anything alloy it touches). It makes short work of dirty engines and you normally will get away with using one can while other spray degreasers will take a couple and are a lot messier to work with. Spray it on, work it with an old paint brush and hose it off like regular degreaser. Been using it for years and if had known about this trick earlier it could've made my life easier...