The 2023 Nissan Z is one of the most exciting vehicles to debut this year. A 400-horsepower twin-turbo V6 and an available six-speed manual transmission make this a prime competitor against the Toyota Supra, which just got a manual transmission of its own. But if you opt for the manual in your new Z, you’ll be getting a slightly quieter exhaust system compared to what you’d get with the 9-speed automatic. And it all comes down to how the drive-by noise test works.
I was lucky enough to attend Nissan’s media launch event for the new Z in Las Vegas last week. I can’t tell you how the car drives just yet—the embargo lifts on May 16th. But when I sampled six-speed manual and nine-speed automatic versions of the new Z back-to-back, I noticed a difference in the exhaust sound, and conversations with Nissan employees confirmed my suspicion: The automatic is slightly louder.
That’s because engineers can tweak the automatic to pass drive-by noise tests while using an exhaust system that’s more vocal in everyday driving. Automotive noise regulations are complex, and vary from place to place, but let’s use California’s test as an example—it’s one of the most stringent in the U.S., and California is enthusiastic about enforcing it.
The test method California uses was designed by the Society of Automotive Engineers (SAE J1470, “Measurement of Noise Emitted by Accelerating Highway Vehicles,” if you want to get into the nitty gritty). The exact parameters of the test are stringently laid out in the SAE paper, but basically, it boils down to this: A vehicle accelerates past a microphone, which measures the sound pressure level in decibels.
The test is designed to measure “the highest noise level consistent with urban driving.” To simulate this, the test demands a full-throttle acceleration from 50 km/h (31 mph) until the engine reaches its peak-power rpm. (The exact details of the test vary based on vehicle size, weight, gearing, and more, but broadly this is how everyday passenger cars are tested.)
Here’s the thing: the methods for testing manual and automatic transmissions differ. In a stick-shift car, the test must be done in either 2nd or 3rd gear; in an automatic, “the throttle shall, as rapidly as possible, be opened as fully as will ensure maximum acceleration without operating kickdown” (emphasis added by me), and held there until the car reaches the end of the testing area. SAE defines “kickdown” as “a forced downshift to the lowest possible gear.”
You see the issue. A manual Z has to do a full-throttle run from 31 mph until it reaches its peak-power RPM, in either 2nd or 3rd gear. Peak power comes at 6,400 RPM. It’s gonna get loud. Meanwhile, the automatic Z only has to putter along in whatever gear it’s programmed to engage at 31 mph, using light throttle so as not to trigger a downshift. And since the engineers knew this, they programmed the automatic to pick a really high gear when cruising at 31 mph.
Hence, the manual gets a quieter muffler to pass the test, while the automatic gets away with a louder setup.
You may remember this drive-by noise test created some commotion back in 2021, when the manual-transmission Porsche 911 GT3 was briefly banned in California because it wouldn’t pass the test. Porsche uses the exact same exhaust system on manual and automatic GT3s, but the auto could be programmed to shuffle through the test in high gear, while the manual was forced to rip a full-throttle run in 3rd. Eventually, Porsche and California reached an agreement that allowed the manual GT3 to go on sale, and the whole thing was resolved before the first GT3s ever reached California dealerships.
But these noise regulations are a big deal, especially when it comes to performance cars. Nissan knows the U.S. will be its biggest market for the Z, and California is almost always the number-one state for sports car sales within the U.S. So Nissan had to adjust the exhaust on the stick-shift Z to make sure it passed California’s test.
Having driven them both, I can tell you this: The exhaust difference between manual and automatic is noticeable, but it’s not night-and-day. Basically, you can hear a little engine murmur at highway speeds in the automatic; in the manual, at constant highway speed in sixth gear, you don’t hear much of anything from the engine. In either car, you get plenty of voice from the twin-turbo V6 at higher RPM.
Drive-by noise regulations have a huge impact on how performance cars are engineered. Jason Cammisa explained it in this excellent video for Hagerty. You know how most automatic-transmission performance cars accelerate more quickly than their manual counterparts? It’s not just because the auto can shift faster—it’s because automakers tweak the gearing on their stick-shift cars to more easily pass the drive-by noise test, and that can have a negative impact on the manual car’s acceleration time. Fascinating, complex, and something most car enthusiasts know nothing about.
There’s some solace for Z fans who want a manual. At Nissan’s launch event, the automaker showed off a stick-shift Z with a prototype sport exhaust system designed by Nismo. Allegedly, the cat-back system doesn’t offer any measurable boost in power or torque. But it does sound fantastic, as this video from—once again—Jason Cammisa points out. The red car is an automatic, the gray car (swipe for the 2nd video) is a manual with the prototype Nismo exhaust.
I know what you’re wondering: Can you simply swap the automatic exhaust onto the manual for a little more tailpipe jazz? From my conversations with Nissan, it sounds like that might not be possible—manual and automatic models use slightly different exhaust path routing. But Nissan is not naive about how the Z will be treated by its owners: A spokesperson told me the company is well aware that lots of Z owners will swap on an aftermarket exhaust almost immediately, no matter which transmission they choose. The automaker invited aftermarket suppliers to take measurements of the Z months ago. You can be sure there will be lots of full-throated options when the Z arrives in dealerships ... sometime.