Nissan made countless enthusiasts happy when it announced its new Z sports car would have a manual transmission and, now that it's here, the Nissan Z is among the last manual-equipped sports cars on sale. However, Z customers that choose the manual transmission won't do so without taking a least a small penalty, in the form of a quieter factory exhaust. Why does the manual-equipped Nissan Z have a quieter exhaust note than the automatic one? Jalopnik's Bob Sorokanich did some digging and, as usual, it's because of U.S. regulations.
The U.S. has pretty strict regulations on automotive engine/exhaust noise, with California having the strictest regulations of any state in the Union. The SAE (Society of Automotive Engineers) developed a test for Californian noise regulations, in which a car must accelerate from 50 km/h (31 mph) at full throttle, past a microphone, under certain parameters, to measure its sound in decibels. Except, the parameters for automatic cars and manual cars are different.
For a manual car, it needs to do the test in either second or third gear at wide-open-throttle. However, an automatic-equipped car needs only to accelerate by using as much throttle as possible without initiating kickdown. That last bit is important, as kickdown, according to the SAE, is “a forced downshift to the lowest possible gear.” Which means the manual car will reach peak-RPM during the test, while the automatic will be programmed to chill in the highest gear possible, far away from peak-RPM.
To pass the noise test with a manual transmission, Nissan had to fit a quieter muffler to the six-speed Z, and, according to Sorokanich, the difference is noticeable.
Not all hope is lost, though. Nissan will be offering a NISMO exhaust upgrade for the Z, which the brand expects most customers to buy anyway, regardless of transmission choice. And even if they don't choose a NISMO exhaust, Nissan is aware that many of its Z customers will upgrade to aftermarket exhausts, which is why aftermarket exhaust brands were already allowed to take measurements of the new Z, months ahead of its release.
For most enthusiasts, a slight reduction in sound isn't going to sway them from buying a Nissan Z with a manual transmission, and it shouldn't. The thrill and engagement of driving a proper three-pedal 'box outweigh any small lack of exhaust noise, especially when you consider that it's an aftermarket upgrade away from sounding better than stock anyway.