The upcoming Nissan Z is one of the most exciting new enthusiast cars. This exciting sports car is offered in both a 6-speed manual transmission and a 9-speed automatic option. Besides the different driving characteristics of each transmission, Nissan was forced to fit a quitter exhaust to the manual transmission Z so it can pass strict noise regulations.
When automakers build cars, they have to consider an endless stream of rules and regulations that their vehicles must meet before being sold to the public. In the case of sports cars like the Z things are even more difficult as automakers work to balance excitement and fun with legal obligations. Even the exciting Z with its twin-turbo 3.0-liter V6 engine has to follow the rules.
All new vehicles must pass noise regulation tests before being sold around the world. In America, the state of California has the strictest guidelines, which means they control the sound of every stock vehicle being sold in America.
The California test is based on a test created by the Society of Automotive Engineers SAE J1470. The basic test requires a car to drive past a microphone. The test starts when the test vehicle is at a speed of 31mph. The vehicle must then accelerate at full throttle until it reaches its peak power RPMs.
The issue lies in the fact that manual and automatic vehicles as tested differently. Manual transmission vehicles must start this test in 2nd or 3rd gear, which means they will reach redline during the test and produce a lot of noise. For the testing of automatic vehicles, the text specifically states that they should accelerate and open the throttle as quickly as possible without triggering a forced kick down or downshift. Instead, automatics accelerate along slowly in whichever gear allows them to achieve 31 mph but not so quickly that the transmission downshifts to a lower gear keeping noise levels to a minimum.
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.