The pipes, the pipes are calling: How Yamaha made the MT-09 howl

Yamaha MT-09 exhaust exits
Yamaha MT-09 exhaust exits
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Yamaha’s engineers have spent countless hours on the dyno and the road trying to perfect the sound of the 2021 MT-09, with its heavily revamped 889cc triple. Now they’ve revealed details of the changes made in an effort to make the most of the bike’s distinctive three-cylinder sound.

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With strict limits to meet, the first job was to minimise noises elsewhere on the bike. As well as giving more leeway within the legal limit by reducing things like gear whine, this meant engineers could make the exhaust and intake notes more noticeable.

Yamaha have also kept withing the noise limits by using Sound-absorbing perforated steel sections on selected parts of the silencer walls help cut noise, while the shape and internal pipe length tunes the exhaust note.

Where the old bike had three long header pipes, merging into one shortly before the main silencer, the new MT-09’s pipes are joined into a single, large exhaust much earlier.

That’s because Euro5 emissions laws require catalytic converters to get up to operating temperature more quickly than Euro4, and moving the cat closer to the exhaust outlet is the solution. Other than that, the belly-mounted silencer looks superficially similar to before, but inside it’s very different.

Yamaha MT-09 exhaust internals

Internally, the old model’s silencer had three chambers. The exhaust gasses were piped into the central one, where they’d bounce about before accessing a connector pipe into the rearmost chamber. From there, a longer connector pipe ran all the way to the front chamber where the gasses had to make another U-turn.

The new bike has what Yamaha call a ‘1.5 chamber’ muffler. There’s a single internal wall that separates the rear two-thirds from the front third. The main pipe takes the gasses through the front chamber and releases them into the large rear one, which is shaped to help reduce sound as they bounce around inside it before entering the front chamber via a large hole in the separating wall.

From there, the gases make a 180-degree turn before entering two pipes connected to exhaust exits on each side of the silencer. This means the four exhaust gas U-turns required for the old design have been cut to two, which results in a free-flowing pipe, gives designers more flexibility over length and shaves 1.4kg of weight.

Yamaha MT-09 exhaust

Finally, the exhaust gas makes its way out of the pipe via two exits rather than the old bike’s single outlet, meaning the 2021 MT-09 comes to you in stereo.

However, exhausts are only half the story when it comes to a bike’s noise – Yamaha also paid attention to the sound of the air entering the engine. The firm say they were inspired by a styling sketch that showed a proposed MT-09 with three exposed air intakes set into the fuel tank that gave them the idea of using multiple, tuned-size intake ducts on the airbox.

More than 50 different arrangements were tried before the final design was picked. Happily, there are still three intakes, but each has a different length and cross-section – and they work like organ pipes so each emits a different sound, coming together in harmony.

Yamaha MT-09 styling sketch

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Ben Purvis

By Ben Purvis