Here's one area where the racers can benefit from a good detailing as much as or more than the show guys. In a race car, reliability is everything. Having a part fail at the wrong time means the end of the day for you. The gauges in the cockpit can only tell you so much & the laptop monitoring your systems can't see everything. The only way to see if a belt is about to cut loose, or a hose is developing a bulge where it shouldn't or cracks around a fitting is by visual inspection. But if your engine bay is a greasy mess, how can you see what's really going on in there?
For a show car, what do you think would happen if the judges give your car high marks, only to open the hood and find more grease than on the bottom of a barbeque grill?
I'm going to figure worst case, there's more grease and oil under your hood than in a small middle eastern country. Have any of you ever heard the term 'fight fire with fire'? In this case it means we're going to start cleaning your engine bay with more oil. Two of my favorites are WD-40 and PB Blaster. Both of these are highly refined oils and very thin - designed to penetrate. These oils will penetrate the grease and sludge covering your engine and turn them into a more liquid form which is easily rinsed off. For a first time cleaning on a really bad engine, you'll want the engine hot (operating temperature). This softens the sludge, making the process easier by giving you a head start.
One of the side benefits of using WD-40 or PB Blaster as a cleaner, is that they're safe for the electrical connections in the engine. I usually start with the underneath of the hood. That way I don?t have crud dripping onto my clean engine like I would if I cleaned the hood last..
The underside of the hood is easy enough. Spray the WD-40/Blaster liberally over everything. When I say everything, I mean it. All those openings in the hood, use the little tube supplied to direct the spray into the crease behind the leading edge of the hood. This is where most hood rust starts, so cleaning it out is really important. You may even consider removing the insulation from the hood so you can get behind it. Extra bad spots should be scrubbed with a soft bristled brush.
Once this 'heavy' cleaning is done, hit the hood with a strong stream of water and rinse off the grease & oil residue. Now things get a bit more conventional. Simple Green is a great cleaner. Safe, biodegradable and non-toxic. Best of all, it works. I normally re-spray the underside of the hood with Simple Green and let it soak. Then I use an old wash mitt and a bucket of water with DAWN dish soap. Rinse by directing a strong stream of water over the surface, taking extra care to try and flush out all the hidden areas. This combination removes all the remaining residue, leaving the hood perfectly clean.
The actual engine bay is a bit more difficult than any other part of the car simply because it has so many tight areas, electrical parts and connectors. Not to mention the multitude of different materials (different types of plastic, rubber, aluminum, steel & painted surfaces) inside. On most cars, the only thing you really need to remove is the stock air intake. If you want to get really serious, There are places that rent engine hoists. Once the air intake is removed, your throttle body is wide open. Obviously mass amounts of water aren't good in here. You can use either aluminum foil, or plastic wrap & a rubber band to seal off the opening. For the major electrical components (alternator, fuse & power distribution boxes, wiring harness connectors etc.) you may decide that you want these items covered before cleaning to prevent their exposure to large amounts of semi-high pressure water. For these items, aluminum foil works best. It's relatively durable, completely water and detergent proof and best of all, stays where you put it.
I personally don't feel the need to cover parts of the engine (other than the TB opening) prior to washing. My way of thinking is that as soon as I'm done, take the car out for a 15-20 minute drive. The combination of engine heat, and airflow from driving will quickly remove most of the water. Driving through a puddle, or driving in the rain will leave more water than what remains after the wash.
How deeply you dig into the engine bay to clean is completely up to you. If you like, divide it into sections to be done on different days. Inner fenders one day and fire wall, radiator support area the next and the actual engine another day. Splitting the job up will help keep you from 'burning out' and lets you do a more thorough job.
For the engine, hoses and other misc. parts, plan on getting pretty dirty yourself. 'Splash back' is going to be a factor here, as will reaching deep into the engine bay to get the lower sections of the engine & firewall.
You will want to use the old wash mitt and make sure you get all sides of the hoses, brackets and other parts. Trust me if you miss something during the cleaning you're going to find it when you next work on the car when you stick your hand in there and it comes back all grimy from an area that didn't get cleaned, or the nice chrome part you're installing winds up covered in crud.
Once you think you've gotten it all, rinse the motor with the garden hose. Start with a strong stream and hit everything. Once the big stuff is gone, switch to a medium spray. This will 'float' the remaining gunk away without splashing it all over the place. There is no way you're going to clean the engine without getting over-spray of cleaners & gunk over the rest of the car (especially the windshield). Occasionally rinse the whole car to remove the crud and prevent it from sticking where it shouldn't.
Once this 'heavy' cleaning is done, stick your head back into the engine bay and look for anything you missed, use your hands to check under and behind parts. This is also the time to check for worn hoses, belts, frayed or melted wires etc. The majority of the dirt & grime are gone, and since you're doing a close inspection of the whole engine anyway? For the racers (or anyone for that matter) having a clean engine lets you spot leaks right away, and it's much easier to tell where the leak is if you can see where it's coming from instead of looking for fresh spill amid a bunch of old grime. Too, if a competitor happens to look in, they're going to see a tight engine compartment and know you're serious about your stuff. Not to mention if something IS broken, you're going to have to stick your hands in there & why get dirtier than you have to?
If you find that the whole engine is now clean (or as clean as you want it) take it for the 'dry off' drive. If not go after the remaining dirt with the wash mitt or other tool needed to reach that area. When you're done with the drive, you'll need to give your car a quick wash of the visible surfaces to remove any residue that splashed onto it from the engine cleaning.
Now is the time to decide if you're going to use dressing on the engine. Some people use a water based protectant (usually a very thin product) and spray the entire engine bay, others use something like BLACK MAGIC, applying it with a cloth to all the proper parts instead of spraying everything in sight. I personally apply wax to the painted areas I can reach and use BLACK MAGIC (cause the wife bought a ton of it at the discount store for me) on the wires, hoses & other plastic parts.
Tips & Tricks:
I haven't tried this, but some have said that on a mildly dirty engine, you can soak the engine & engine bay with ARMOR ALL then let it soak over night. The next day, spray everything down with a strong stream of water. This is supposed to wash away the grime & excess ARMOR ALL and leave a nice gloss.
Make sure to clean the fan blades (electric or belt driven), dirty blades don't flow air as well and may contribute to overheating. After an intense cleaning make sure to re-lubricate the hinges, you just stripped them clean of grease.
A wet/dry vacuum with a crevice attachment can also be used to dry the engine, as can compressed air. Be careful with compressed air though, it can force water where it doesn't belong.
When you are cleaning your engine with just soap and water, you want it cold. Otherwise the soap will dry out too fast, forcing you to use even more soap and making things harder than they have to be.