Nissan had to quiet down the exhaust on manual Zs because they are tested differently thank automatics.
The Nissan Z is one of the most anticipated new enthusiast vehicles. This thrilling sports car is available with a 6-speed manual or a 9-speed automatic transmission. Aside from the differences in driving characteristics between the transmissions, Nissan was required to adapt a quieter exhaust system to the manual transmission Z in order to meet rigorous noise requirements.
When automakers design cars, they must consider an unending list of laws and regulations that must be followed before they can be sold to the general public. Things are much more challenging in the case of sports vehicles like the Z, as automakers have to strike a balance between thrill and fun and regulatory duties. Even the thrilling Z, with its twin-turbo 3.0-liter V6 engine, must adhere to the regulations.
Before being sold around the world, all new automobiles must pass noise regulatory testing. California has the strongest regulations in the United States, which means they regulate the sound of every stock vehicle sold in the country.
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The California test is based on SAE J1470, which was developed by the Society of Automotive Engineers. A car must drive through a microphone in order to pass the basic test. The test begins when the test car reaches 31 mph. The vehicle must then accelerate to its maximum power RPMs at full throttle.
The problem is that manual and automatic automobiles are tested in different ways. Vehicles with manual transmissions must begin the test in second or third gear, which means they will approach redline and make a lot of noise. The wording expressly stipulates that automatic vehicles should accelerate and open the throttle as rapidly as possible without triggering a forced kick down or downshift during testing. Instead, automatic transmissions accelerate slowly in whatever gear permits them to reach 31 mph, but not so quickly that the transmission downshifts to a lower speed, reducing noise.
This is why Nissan’s new Z is louder with an automatic transmission when compared to the manual transmission Z. Thankfully manual transmission Z owners can easily fix their quitter exhausts with an aftermarket option.