An exhaustive search for an exhaust system is exhausting! Okay a bit too much there, I know, I couldn't help myself. I've spent years researching the best exhaust system upgrade for a 370Z. I've watched countless youtube videos, read dozens of forum posts, and tuned an attentive ear to the exhaust sound of every Z driving by to identify the setup. It hasn't been straightforward because an exhaust 'upgrade' can mean such different things to different people. There are so many options on the market that cater to individual preferences, which is great, but it makes it that much harder to choose a single one.
Motivation
Let's take a step back and start with the why, why upgrade the OEM exhaust? Consider the 350Z / Z33 chassis. The then re-invented Nissan Z-car of the early 2000's featured one of the most iconic factory exhaust system notes of a mass produced sports car I can think of. Most factory cars generally produce notes that range from nothing, to the whirr of a leafblower. This is largely due to emissions regulations and NVH considerations on a broad scale. The 350Z (as well as the G35) instead featured a truly beautiful and unique exhaust hum, that sounds like "voummm". This unique note has made these cars instantly identifiable to this day, whether in a parking lot or driving down the street.
For some strange reason (likely further stringent emissions), however, the 370Z / Z34 chassis did not receive this exhaust endowment from its predecessor, despite sporting a VQ engine with similar roots and configuration. From the factory, the 370Z's exhaust is definitely on the nothing end of the range. While that's sufficient for an Altima, Maxima, or even a Q60, this is quite strange for a flagship sports car. Perhaps some CARB/DOT requirements changed towards the tail end of the 2000 - 2010's, but the substantially upgraded Z34 features quite a downgrade in the exhaust department, at least from a sound perspective.
Sound Perspective
This begs this question, what is a 'good' sounding exhaust? This means many things depending on who's asking. Common attributes are tone, volume, and rumble, along with side effects of drone and raspiness. The best exhaust system is one that provides sensational sounds while driving that make a driver feel more engaged and more excited in the driving experience. However, it must do this without making the car annoying to drive and, to some extent, not be obnoxious for others.
Most exhaust systems excel in only a couple of these areas and fail miserably at the rest. For example, you can get amazing tone and volume, yet be stuck with drone that rings in your ears while cruising down the highway at 3500 RPM. Or you might find no drone, but a raspiness that makes you wonder if the car has an exhaust leak. Still, you might have the best tone, no drone, no rasp, but have something that is just way too loud to be bearable on a day to day basis.
These are just some examples of the actual attributes on the many different exhaust systems available on the market for this car.
Performance
Then, of course, there's the performance side of things. Naturally, an exhaust system upgrade should offer decreased restriction in the airflow for exhaust gases, optimally resulting in improved power output. This isn't always the case, however, especially while sticking to a factory tune. Such modifications can decrease needed backpressure in the system, which can reduce net power for turbocharged engines.
A reduced output restriction in the exhaust system may contribute to an increase in overall airflow that exceeds MAF/MAP air metering system's limits, although this is unlikely for an isolated exhaust system upgrade. Perhaps along with the addition of an intake upgrade, and definitely when going with forced induction, the air metering system's limits need to be considered and factored into the tuning strategy to reduce the possibility of a lean condition that could lead to knock and engine damage.
Weight
Weight savings are another major consideration on an exhaust system for the Z34. This is a big area, not only because of the piping design and material selection, but also because of the available configurations of dual or single-exit. Single-exit offers a further reduction in weight.
Configuration
The factory system uses a dual-exit tailpipes, preceded by a combined and split H-pipe style setup, attaching to the catalysts. Switching to a single exit is a common option that can offer a huge weight savings vs. the standard dual-exit. If one is building a track focused vehicle, a single exit may be a no-brainer. If one plans to drive the vehicle on the road often enough, a dual exit may offer greater livability.
Goals
It all boils down to what your individual goal with the car is. Are you building a time attack track monster that will never see public roads? Do you commute often but want a better soundtrack? Do you want to be louder than your neighbor's Charger? Do you just want the car to look cooler with those burnt titanium blue tips? These factors will weigh heavily on your decision.
For me, the vision of the car was clear from the get-go, mostly in-line with what the Z actually is from the factory. A touring (road) car first, that can be used for sporty occasions. The stock muffler setup does not offer enough of a sporty feel, so I wanted to add more of that, without making the car annoying to drive on the roads.
This is tough. Most options out there will offer an increased noise output, but very few can do so without sacrificing the drivability of the car. In fact, it's incredibly easy to make a car louder and 'decrease exhaust restrictions' by simply unbolting the exhaust system from the car. Drop all the pipes and you have a loud car. A very annoyingly loud car.
It takes real engineering to make a car louder, while retaining driveability. With that lead-in, you might already know where I'm heading.
The Decision
Still, after years with the stock exhaust on the car, I was nearly fully convinced that an ultra loud, single exit, full titanium exhaust was the way to go. This means Race car, I thought. But at the end of the day, I couldn't find comfort in choosing this option. The car is not a racecar. It has full interior, is stock-bodied, and stock engined for that matter. Why put a blaringly loud titanium single-exit exhaust on an otherwise civilized car? Because it sounds cool. I know it does, it sounds awesome. I almost caved in for the coolness. I almost went for a Tomei, bro.
Having been around cars with straight pipes, loud exhausts, or no exhausts, there's one thing I've learned. At some point in the drive, you just want to turn down the volume and cruise. Yeah that cold start sounds amazing (to you but not to your neighbors), yeah it sounds so good when you are in the mood to blip the throttle and hear the downshift. But at some point, if this is a cruiser or even a commuter, you just want to tone it down, maybe take a phone call, or hear yourself think. Maybe not 10 minutes into the drive, but maybe 4 hours along the way to ButtonWillow, or along the PCH cruise. Sure, those loud hooning cars sound amazing when they fly by, but what about what it's like for the entire rest of the drive?
I finally arrived at deciding it wasn't worth sacrificing the driveablity of the car MOST of the time, just to make it sound amazing SOME of the time. I figure, most of the time I am just cruising around, and really only some times do I wanna open it up and hear the engine sounds. With the stock exhaust, even then there was not much of a sound response. Another factor to consider is that many newer cars have active exhaust systems. They sound amazing on a flyby, but guess what, they don't sound like that all the time. The valves close off additional output paths and the car becomes more civlized on demand. For this reason, I strongly considered simply adding an electronically controlled exhaust cutout system that welds on and with a switch, can shift over to full open-exhaust mode. I'm glad I decided against this route in the end, due to the added weight of the system from stock, and no real exhaust gas flow optimization, aside from the dump.
The HKS Hi Power dual exhaust system was the final choice. A true dual-type system which replaces the factory Y-pipe for dual pipes that continue separately all the way along till the tips. Although it is heavier than any single exhaust, and definitely more than a titanium setup, I preferred the stainless steel construction over an ultra thin and light titanium walled setup for better sound dampening qualities. The 2.5"? piping is carried all the way through unlike in the stock setup which steps down in diameter.
Perceptions
Sound
This exhaust gets a rap for being 'the quietest' option out there, which naturally many might avoid when making a noise upgrade. Indeed at low RPM's and putting around, I almost can't even tell there's an upgrade. It fades away and actually feels like there was nothing modified on the car. However, at WOT (wide open throttle), things change very fast. The sound steps up an octave and suddenly the car is hitting all the right notes. It's truly an exquisite piece of engineering. I really didn't think it was possible for an exhaust upgrade to sound so good in a sporty driving scenario, yet remain so incredibly civilized at low load part throttle. It's the closest thing to an active exhaust system available on the market, yet better in every way.
Performance
I honestly went into this not expecting much on the performance side of things. It's a stainless steel, dual exhaust setup that offers some weight savings but not much compared to a single exhaust setup. However, I was blown away on the first drive. Without even a tune, the car instantly showed a major power boost as validated by the butt-dyno. The weight savings, combined with the increased airflow had a major effect. I'm truly surprised that even without a tune, the performance bump was evident and immediate. It must be that the stock map allows for enough additional airflow and corresponding fuel which are needed for this new exhaust setup.
Aesthetics
Okay okay, dual exit tips look pretty solid in the 370Z's rear bumper design which features cutouts for the mufflers. I kind of wanted to get a single exhaust just because of all the haters who complain about sporting a single exit in a dual-exit designed bumper. It's the tuner look on Skylines, RX-7's, etc, that make the single exit look so appealing to me. But I definitely can't complain about the dual exhaust setup for this car. It looks proper. Especially with the burnt titanium blue tips that fill the openings very nicely.
Conclusion
The HKS exhaust setup adds sound, performance, and looks all the way around. This is the optimal setup for me. It offers many of the pros of an exhaust upgrade with literally none of the cons. It's a well designed and well engineered setup. mA the car immediately sounds better, looks better, and drives better without driving any worse or being any less liveable than it was before (just watch out for scraping those giant tips on a deep driveway).
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After a few months with it, it is still a tad on the quiet side. However, I believe a louder exhaust setup after the cats is not the solution, that will only lead to the common raspy Z exhaust notes heard in many a town. I am convinced that headers combined with the HKS catback will produce the optimal exhaust note. Increasing the volume upstream at the headers may be the solution for a bit more rumble, while retaining the sound dampening characteristics of the silencers downstream. This hunch is coming from my experience riding in a Hako in Japan with a swapped in Toyota 1UZ-FE V8, which sounded simply outstanding with a header upgrade. If it worked on the V8 it just might work on te VQ? We'll see iA.
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