My votes...
Duesenberg SJ
Most variations on the Ferrari 312 motor are wonderful.
The BRM 16
Honda made a nice F1 motor too.
1932 Maserati 8C 3000
Not so much "beautiful" as "brutal" is the Porsche 935.
And if motorcycles count, you gotta have the Indian Four...
...and the Vincent motor.
1000HP 2.6L Ford 4-cam Indy Turbo V8 in a custom falcon.
http://bringatrailer.com/2009/07/30/ready-for-lift-off-1962-4-cam-falcon/
Wärtsilä-Sulzer RTA96-C:
a two-stroke turbocharged low-speed diesel engine designed by the Finnish manufacturer Wärtsilä. It is currently considered the largest reciprocating engine in the world, designed for large container ships, running on heavy fuel oil. It stands at (13.5 metres (44 ft)) high, is 27.3 m (90 ft) long, and weighs over 2300 tonnes in its largest 14-cylinder version — producing 109,000 brake horsepower (80,08 MW).
(Yeha22 already beat me to the SJ...)
This one was a beauty to me. Since it was completely trashed, I got the car for free.
Edit: Ok, the URL is either broken or it won't show up due to the firewall here. I can't tell which.
I'll shamelessly insert my favorite engine I can got out to my garage and ogle :)
British Leyland "A" engine. 1275cc, .040 over, balanced recip assy', 12:1 CR, Megadyne 266 can, recurved mechanical advance 45D distributer, Weber 45DCOE w/ 40mm chokes on 6" Cannon manifold, crazy valve train geometry that required machining the rocker towers, etc, etc,
Note: Look at the throttle linkage!
Points for the blue exhaust headers.
Anything from Troy Trepanier.
I know it's a train, but it is basically all engine!
And that is how you do a bundle-of-snakes intake!
@GrantC here is the same thing, but for the V-12 Jaguar E-Type.
And for good measure, here's some Lamborghini Muira V12s waiting to be installed.
Both of those images came from my blog.
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