If what you're trying to clean off is an organic compound - which, if it's in or around an engine, it probably is, and if what needs to be cleaned has ZERO rubber or "plastic" parts of any kind - then a commercial kitchen cleaner may be the ticket, as it is 100% safe on aluminum. I have one called "Carbon Off" - you can get it at a commercial kitchen supply store. Just looked at its active ingredients, which are, in order: Dichloromethane, "Aromatic hydrocarbon" (whatever that means. The code for that particular nasty is: 108-88-3) and Methyl Alcohol.
Again, just do not let it get near anything non-metallic, although I would be interested to know how teflon responds to it.