The BMW i8 was a strange car for many reasons. It had butterfly doors but wasn’t an uncompromising supercar; a hybrid powertrain incorporating a three-cylinder engine, but wasn’t an econobox; and a carbon-fiber monocoque at a time when the only other vehicles that did, save for BMW’s own i3 and the Alfa Romeo 4C, were exotics at least twice its price. Some might call it compromised, but there’s no denying the i8 was truly unlike anything else on the road—even down to how it made sound.
Sure, plenty of modern cars have manufactured, synthetic sound. The practice is regretfully more commonplace today than it was 12 years ago, when the i8 first went on sale. Some EVs even broadcast fake growls, pops, and bangs to bystanders. The i8 did have a small gas-burning engine, so of course it made a little noise, but BMW evidently felt it necessary to supplement its exhaust note. But you’d have to crack open the service manual or take a peek under the car to get a clue as to how exactly the engineers decided to go about doing that.
See, the i8 looks as if it has two tailpipes behind its rear bumper. The one on the right is indeed connected to the engine. The other, though, isn’t connected to anything—well, technically it is, but only with some speaker wire. You see where we’re going with this.
Yeah, the i8’s left exhaust was really just a loudspeaker this entire time. And boy, does it get loud, as Trevor Elam, who runs the BMW parts site Bimmernetwork, shared on YouTube:
“We discovered [the speaker] during disassembly when the BMW service manual mentioned removing the acoustic generator,” Elam told me. Indeed, the manual refers to this part as both an “acoustic sensor” and “sound generator,” meaning that even BMW—the brand that gave us the world’s first “Sports Activity Vehicle”—doesn’t care to sugarcoat what this part really does.
In the clip above, Elam connects the sound generator to a stereo, proving that it can indeed be used as a normal speaker. I asked him if he thought about transforming this thing into an entirely impractical portable speaker, maybe for a party. It’s got the power for it; a recent Hagerty video measured the sound this thing produces at a whopping 110 dB. That’s supposedly about as loud as a rock concert.
“We did use it as the speaker in the shop for a day or so, it is actually quite loud,” he said, noting that it’s tuned for high bass above everything. Makes sense for a speaker that’s specifically designed to project engine sounds.
This i8 shouldn’t need the speaker’s help, considering the plan Elam has for it: A B58 inline-six with a Dynamic Autowerx turbo stuffed into the front end, targeting around 700 horsepower at the wheels. He says he doesn’t anticipate trouble hitting that sum, given that his B58-equipped drag 340xi makes 1,000 hp.
Elam also showed me a message sent to him by a BMW engineer who helped develop the i8 back in Germany. He endorsed the project and said that his team hoped someone would eventually “install a proper engine” into the hybrid sports car. Now, somebody’s doing exactly that, giving the i8 a motor to make the sound it could never produce authentically (and then some). If you’d like to follow along, Elam is documenting the whole process in episodes over on his YouTube channel.
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