The blast, when it came, was loud without being overwhelming. We were close enough that there wasn't more than a quarter second's delay between the flash and the sound, and I felt the warmth of burning kerosene exhaust roll over me. The gas generator spoke with a deep rumbling, topped with a rocket's crackle-crackle-crackle—a sound I'd always thought was just the microphone clipping when listening to recordings of rocket launches. The overall noise of the thing was impressive—probably about as loud as a loud rock concert—but we were far enough away not to need hearing protection. The gas generator produced a long horizontal column of flame, which held steady for the entire test. It was impressive, but it was even more impressive when I reminded myself that in a real F-1 all this fire and noise and smoke was merely used to drive the machinery that fed fuel into the engine for the real fireworks.
Via Instapundit [1], “ How NASA brought the monstrous F-1 “moon rocket” engine back to life [2]”
I did know know that the F-1 rocket of the Saturn V (of which there are five as part of the first stage) were actually two rockets—the smaller, producing 55,000hp (horsepower) just to drive the pumps of the main rocket (producing approximately 32,000,000hp—remember, that's just one F-1 rocket).
I also did not know that there existed quite a number of F-1 rockets, and as the article states, there's a group working to test fire an F-1 rocket. It's pretty amazing to think that these are still the most powerful rockets every produced and they're over 40 years old.
Simply amazing.
[1] http://pjmedia.com/instapundit/167094/