What makes the “broom” noise in a car/motorcycle engine?
In: Engineering
Gasoline being ignited extremelly fast inside the cilinders of the engine makes that noise, they are just a series of really quick explosions.
On a typical v8, idling at 800 rpms,
800 rpm / 60 seconds = 13.3 turns per minute.
13.3 turns * 8 cylinders / 2 (4 stoke fires every two turns) = 53 ignitions per second, or each cylinder fires 6.6 times per second.
Most vehicles are turning 2000-3000 going down the highway, which translates to an 130 – 200 ignitions per second.
On the loud side, ever heard a two stoke dirt bike, which sounds like its turning 9,000 rpms? (ignoring, they actually are turning twice that)
Since they are two stoke, they fire every revolution.
But, a yz85, which can turn 12,000 rpm..
https://www.cycleworld.com/story/buyers-guide/2020-yamaha-yz85/
Has a single cylinder, which fires one per rpm.
12,000 / 60 = it is firing 200 times per second at redline.
Edit-
Updated post to reflect overall engine ignitions per second, rather then per-CYLINDER ignitions per second.
As a bonus, the 2019 ferrari F1 engine, redlines around 15,000 RPMs.
15,000 (RPM) / (60 seconds) = 250 turns per second / 2 (4 stoke) * 6 (cylinders) = 750 explosions per second.
Edit 2-
My original math was incorrect by a large. The issue has been corrected and the above statements are updated.
Some of it is mechanical but it’s mostly air: Exhaust through the exhaust system; Air intake volume comes into play with larger displacements.
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