The Napier Deltic engine had a totally unique sound to its exhaust because of the very unusual firing sequence of its 18 cylinders (more info after the jump). Here’s a few Class 55 Deltic locomotives at work; the best sound happens at round 3:00.
The Deltic’s unique sound is not just because of the firing order though. Here’s an explanation from Wikipedia:
Being an opposed-piston design with no inlet or exhaust valves, and no ability to vary the port positions, the Deltic design arranged each crankshaft to connect two adjacent pistons operating in different cylinders in the same plane, using “fork and blade” connecting rods, the latter an “inlet” piston used to open and close the inlet port, and the former an “exhaust” piston in the adjacent cylinder to open and close the exhaust port. This would have led the firing in each bank of cylinders to be 60 degrees apart. However, it was decided to arrange that each cylinder’s exhaust piston would lead its inlet piston by 20 degrees of crankshaft rotation. This allowed the exhaust port to be opened well before the inlet port, and allowed the inlet port to be closed after the exhaust port, which led to both good scavenging of exhaust gas, and good volumetric efficiency for the fresh air charge. This required the firing events for adjacent cylinders to be 40 degrees apart. For the 18 cylinder design, it was possible for firing events to be interlaced over all six banks. This led to the even, buzzing exhaust note of the Deltic, with a charge ignition every 20 degrees of crankshaft revolution, and a lack of torsional vibration, ideal for use in mine-hunting vessels.
A bit complicated, but it’s what gives the Deltic the “edge” to its already unique sound. I can only imaging what the Superpumper sounded like at full chat.
So what’s your favorite engine sound? If you want to embed a YouTube video, just copy its url (from the browser) and paste it into your comment.