My guess would be to try to minimize water intrusion into the coil packs and other electrical sensors and things that don't handle repeated soakings very well. Might have something to do with the problems associated with engine cleaning and EFI.
Deterrent to amateur fiddlers, possibly.
I worked for a Chrysler dealer when the Hemis were new on the lot, I thought they had a black crinkle finish of the valve covers, but I could be suffering from old mans memory disease. First new one was the 66 Satellite with the HP2 (squared) emblem and solid lifters. Idled at about 1200 RPM.
The Hemi was an amazing engine, saw a recent comparison of that eral of big blocks and it was even close between the big 3 with the Hemi making more than 800 HP from the factory. I like the 55 300 series with 4 wheel disc brakes and the early Hemi.
Now when you talk about beautiful engines I go back a lot further than the 60's.
The late twenties Delage grand prix engine with over 60 ball and roller bearings. Duesenberg's huge straight 8. The early thirties cadillac V16. Of course the Alfa's and Ferrari's were beautiful engines. Bugatti's that had integral cylinder heads. You had to drop the crank out of the bottom to do a valve job!
The first cross flow Hemi engine was in 1907, a Welch I believe. Could be wrong, that book is probably 40 years old.
I don't think the covers are supposed to deter DIYers. The one on my GMC looks really easy to remove, maybe two screws and up it comes. The one on my VW is just friction-fit, you pull and it comes right off.
Yeah plastic can stop emf radiation if it is made conductive with the right materials and my xB engine cover gets plenty of dust and water streeks on it - no I don't have gaping holes to the ground in fact I can't see the ground in my engine compartment because of the stock belly pan and the rather short hood length and very tall engine under the hood - the top of the engine is about 4 feet above the ground.
NOW all you hemi lovers WAKE UP!! The only reason they domed the piston and hollowed out the head was to put TWO BIG VALVES in there at a big angle because back then they didn't know how to put four or six valves in the head per cylinder. Dome pistons have more combustion heat exposure, lower thermal efficiency and more mass than a flat top piston of the same bore.
The 5.7L HEMI Ram for 2009 makes 390 hp and 407 ft-lbs from 345 cubic inches of displacement. The 2009 5.7L Toyota i-Force V8 makes 381 hp and 401 ft-lbs from the same 345 cubic inches of displacement.
1.130 HP per cubic inch out of a 2-valve pushrod V8 (EPA 14/20)
1.104 HP per cubic inch out of a 4-valve DOHC VVT-i V8 (EPA 14/18)
Well first of all the Hemi runs a single cam shaft so the cam timing can't be varied. Efficiency is not measured in HP but in MPG and for a Tundra to get over 20mpg of actual driving mileage with an automatic in the big 5 passenger version like a friend of mine has is pretty efficient. The thing is HUGH - the outside mirrors have power folding so you can fit it in a garage door.