I flew on a Lockheed Super Constellation when I was ten, fall of 1956. I was in the aircraft when the engines were started after a refueling and maintenance stop, about four hours. Engines were pretty cold. The machine had four R-4360 Turbo-Compounded engines, 3,600 hp - ish.
I was watching the engine crank over, a few cylinders would fire one at a time, not enough to get her spinning. With each cylinder explosion the airplane would ring like a bell, shake all over. Clouds of smoke from the single cylinder's exhaust rose hundreds, really, hundreds of feet into the air. Then the engine caught, the prop raced ahead. The whole aircraft twisted, a jump and a twist, and moved feet, not inches. Needed a seat belt to stay in your seat.
The roar is beyond description. The cabin sound pressure level in flight - and the airline bragged about all of the sound proofing installed, and how quiet the machine was to fly in - was, looking back, well over 100dB, maybe 110 dB on the A scale. You had to put your lips about three inches from the other person's ear and shout. Truth. Quite a gadget. A DC-6 is much less dramatic (four R-2800s).
Love radials, the bigger the better.
The only prop planes I got to fly on were military types and they were probably turbo-props by that time. I was on the Hercules, Caribou and Provider. Those were load enough. Seen film of B-17's starting up,impressive.
I had the pleasure and priveledge to be standing about 100ft behind a Corsiar when the engine was fired-up one time. It was located between two metal hanger buildings that were about 200ft apart. The noise and reverberation was intense. I know I was grinning ear to ear!