Dumb question - maybe., Why does a flat-four sound so different? Options

[Alfred]

Why does a VW flat-four sound so different from an inline-four? Don't they both get a power-stroke (spark plug fires) every 180 degrees of crankshaft rotation? The air-cooled flat-four also has some kind of "whistling" sound to it that's very unique. Just curious.

Alfred

[need4speed]

My Type 1 has had both a 1600cc 912 engine, Dual Dellorto DLRA 40's, Busrch Exhaust, and the current engine, a stock 1600cc dual port, with the stock exhaust and carb.

The main difference between the two engines is valve geometry. (IMO).

The 912 gave me much more power, and a much wider range of RPM. The carbs were noisy! There was the constant sucking sound. Then there was the whine of the cooling fan - almost turbine-like (gave me chills) - and the exhaust note . . . buhwaaaaaaah! Absolutely in stark contrast to the VW engine.

About the only thing in common was the valve-train noise, which is a component that sounds much like a battery of a dozen sewing machines in a Panamanian sweatshop. Both engines had this sound, and it was very similar - and would even change audibly as valve-lash drifted out of spec over the miles. (I'm fairly anal about valves - I adjust them every 1000 miles religiously, and I record how far out of spec each one is).

The VW engine's carb has a sucking sound (which varies by how far out you adjust the bypass screw), but it's a lot different, it's a single voice, the 912's Dellortos was a barbershop quartet. That's even running a bad aftermarket aircleaner. The stock oil-bath aircleaner does a great job at muffling noise from the stock 34-PICT carb.
But the big difference was the exhaust note, IMO - the VW has the pea-shooters, and it "fweems". Chirps like a bug, and I'm told this was done on purpose for the US market, a decision made back in the late 1940's or early 1950's, that went along with calling the car a "Beetle". There are inserts in the pea-shooter tailpipes that cause the moving gasses to whistle. And those inserts do wear out over time - and can be removed as well.