Some sounds will stay with me forever, the Rolls Royce Merlin(s) in a Spitfire, Hurricane, Mosquito, P51 Mustang etc., a Boeing 777 starting up on the other side of the airport, the three guitar attack of Lynyrd Skynyrd's Gibsons, an Aston Martin Vanquish hitting the redline as it makes a full bore start. And one is the sound of a Detroit exhaling through a pair of upright stacks.
Luckily for me there are two or three where I work and every now and then they're fired up so I can still get my aural fix every now and then.
What was quite unusual was that they were modular engines, the most popular versions being the 53,71 and 92 Series, I used to drive a BedfordTM with the 6V92TAA Detroit in it. They used to look a bit smokey, but almost any truck of 10 or 14 litres with vertical stacks is going to look dirty as the smoke is seen against a light sky.
Actually, no excuses for this one, I think the Pump Timing needs a good dose of looking at.