Engine bay aero?
 

OK, we all know that the engine bay is very dirty aerodynamically.
In most cars we can't avoid passing some air there.
We also can't make the flow there clean, far from that.

The question is:
Can we make the airflow cleaner than otherwise? Cleaner enough to be worth the effort?

In my car, Honda went through some lengths to direct the air which passes through the radiator, out through the wheel wells rather than the rear of the hood or the bottom of the engine bay. Presumably there was a reason for this, but I have no data or facts to support this.

What let's air out can also let water spray filled with road salt in.

This will corrode the electronics.

However, it may take many years to do this.

Today's electronically dependent cars have design measures to avoid this, most designs over 20 years old do not - in my opinion.

Think twice before you let the devil in.

I definitely get road salt in the engine bay. Thankfully most stuff is aluminum in my car. I've considered making baffles to block spray.

I've been thinking about fabricating something to cover the rear well area to prevent salt from getting in. What's wrong with air exiting underneath the car? Seems like the airflow under the car would keep the exhausted air flow attached.

Unsure. Might make it a high pressure zone? Just a guess.

I don't think I get salt in from the rear/bottom, but the tires throw salt all over the catalyst when turning, which is probably why they rust so badly. I could also see salt affecting the coil packs on the back of the engine.

I used to get salt and stuff from underneath until I installed Scott's belly pan (which I had to retrofit because the OEM one was like ripped off with the bolt threads rusted in) but the pan is shielding the engine now. I still get crud and stuff in through the wheel wells though. Don't want that, plus there's a risk of that crud somehow getting caught up into my WAI.

Depends on the car. My Superbeetle has a positive displacement pump that moves air from the engine compartment into the shrouding. Streamlining is not an issue.

The Dasher has a rat's nest of hoses and cables and wires. More modern cars have coils right next to the spark plugs and covers for the bumpy bits. Look for show car engine compartments, the have flattened firewalls and hidden wiring.

Most of the internal drag is in the radiator itself.

engine bay
 

*an old metric was,that the cooling system could constitute up to 12% of a vehicle's overall drag.
*over the years,automakers have improved on that,with fake grilles,active shutters.
*the 1963 Walter Korff' Chrysler Charger Daytona cooling system would cover the inlet portion of drag,with it's 1/6th-height grille inlet,and fully-ducted passage to the radiator.
*to reduce from there,you'd have to fully duct the extractor portion,with contoured tuned outlets located at low pressure regions on the body.Ferrari has spent over $100,000 to develop a working system such as this.For one specific car.
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The lowest drag cars are electrics,with virtually zero cooling systems,or ICE vehicles,with closed fronts,and rear radiators of integrated,aerodynamically-tuned design.Again,$hundreds of thousands.

I think on your own front engine car, the best you can do if you have a really big grille would be block part of it off and make some ducting for the radiator right? It would be very difficult to tell how the air flows through the engine bay and modify fenders or the hood accordingly.