If you've spent more than five minutes on a forum or in a Facebook group, you already know that picking up some frs unequal length headers is pretty much the first thing every owner thinks about. It's the "rite of passage" for the ZN6 platform. Let's be real for a second: the stock FRS sounds a little bit like a sewing machine from the factory. It's quiet, it's polite, and it completely hides the fact that there's a boxer engine sitting under the hood. For a lot of us, that just won't do.
The main reason people go down this rabbit hole is for that "Subie Rumble." Because the FRS uses a Subaru-sourced FA20 engine, it has the potential to sound like a classic WRX or STI. However, Toyota and Subaru shipped these cars with equal length headers to keep things efficient and smooth. To get that signature off-beat lope, you have to swap out the manifold for something with pipes of different lengths. But is it just about the noise, or is there actually some "go" to match the "show"?
Why Everyone Wants the Rumble
The physics behind frs unequal length headers (or UEL for short) is actually pretty simple. In an equal length setup, the exhaust pulses from each cylinder reach the collector at perfectly timed intervals. It's efficient, but it sounds like a high-pitched drone. With UEL headers, the exhaust gas from one side of the engine has a longer path to travel than the other. These pulses eventually collide or "stack up" at the collector, creating that rhythmic, thumping sound we all love.
Honestly, it changes the entire character of the car. Suddenly, your 2.0-liter sports car sounds like it has some actual muscle. It's a deep, gutteral growl that makes downshifting under an overpass feel a lot more rewarding. But before you go throwing your credit card at the first shiny piece of stainless steel you see, there are a few trade-offs you need to understand.
The Battle: UEL vs. Equal Length
If you talk to the "track rats" or the guys chasing every last tenth of a second, they'll probably tell you that UEL headers are a mistake. From a pure performance standpoint, they aren't wrong. Equal length headers (EL) are objectively better for top-end horsepower because they allow for better scavenging. They help "pull" the exhaust out of the cylinders more effectively, which usually results in a higher peak power number on a dyno.
But here's the thing—most of us aren't living at 7,500 RPM on a racetrack every day. For a daily driver or a fun canyon car, frs unequal length headers offer something the EL guys often miss out on: character and mid-range "oomph." While you might lose 3-5 horsepower at the very top of the rev range compared to an EL setup, the UEL design is fantastic for addressing the biggest flaw of the FRS engine.
Fixing the Infamous Torque Dip
If you own an FRS, you know exactly what the "torque dip" is. It's that annoying flat spot between 3,500 and 4,500 RPM where the car feels like it's suddenly towing a boat. You're accelerating, everything feels great, and then the power just vanishes for a second before picking back up again.
Installing a set of frs unequal length headers is the single best way to kill that dip. When you pair these headers with a decent tune, you fill in that hole in the powerband. It makes the car feel much more linear and responsive in the city. You don't have to downshift two gears just to pass someone on the highway anymore. For many owners, the improved drivability in the mid-range is way more important than what the car does at the absolute redline.
Quality Matters More Than You Think
You're going to see a massive range of prices when you start shopping. You can find "no-name" headers on eBay for $200, or you can spend $1,200 on a handcrafted piece from a boutique shop. It's tempting to go cheap—after all, it's just some metal tubes, right?
Wrong. Cheap frs unequal length headers are notorious for a few things: cracking, terrible fitment, and thin flanges that warp under heat. There's nothing more frustrating than spending four hours under your car wrestling with a header that won't line up, only to have it start leaking three weeks later.
If you're looking for brands, names like JDL, Tomei, and Borla are the ones that usually come up for a reason. They use thicker stainless steel and better welds. Tomei, for example, is famous for their titanium and thin-wall stainless options that are incredibly light. JDL is often praised for their "handmade in the USA" quality and the fact that they offer a lifetime warranty. If you're going to do this job, do it once and do it right.
Installation and the "Hidden" Costs
Installing frs unequal length headers isn't incredibly difficult if you have a decent set of sockets and some jack stands, but it's not exactly a walk in the park either. You'll be working in some tight spaces, and you'll definitely want to spray your factory bolts with some PB Blaster or WD-40 a day before you start. Those heat-cycled bolts love to snap.
There are also some things people forget to buy. You must get new gaskets. Don't try to reuse the OEM ones; they'll almost certainly leak. Most people swear by Grimmspeed gaskets because they're thicker and seal up better than almost anything else.
Also, think about heat management. Headers sit very close to the oil pan and some sensitive plastic bits. Some headers come ceramic coated, which is awesome for keeping engine bay temps down. If they aren't coated, you might want to look into header wrap, though that can be a polarizing topic (some say it holds moisture and causes rust). At the very least, make sure you aren't melting your radiator fans.
Tuning: The Step You Can't Skip
I see this all the time: someone installs frs unequal length headers, starts the car, loves the sound, and then gets a "Check Engine" light ten miles later. Most aftermarket headers are "catless," meaning they remove the primary catalytic converter. The car's computer is going to notice that the exhaust isn't being cleaned properly and it's going to freak out.
Beyond just the annoying light on your dash, the car won't be running optimally. To actually get the performance gains and fix that torque dip we talked about, you need a tune. The most popular option is the OpenFlash Tablet (OFT). It's a "plug and play" device that comes with pre-loaded maps specifically for UEL headers. If you want to go more high-end, an EcuTek tune from a professional tuner will give you the absolute best results tailored to your specific car.
If you don't tune the car, you're basically just making noise. You might even lose power because the engine's air-fuel ratios will be all over the place. Budget for a tune at the same time you buy the headers.
The Drone Factor
One thing nobody tells you is how your choice of frs unequal length headers will interact with your exhaust. If you already have a loud, "fart-cannon" style catback exhaust, adding catless UEL headers is going to make the car incredibly loud. We're talking "wake up the neighbors three blocks away" loud.
It can also introduce drone—that humming sound that vibrates your brain when you're cruising at 70 mph on the highway. If you're worried about it being too much, try to pair your headers with a "quiet" catback like the Invidia Q300 or the CSG Touring exhaust. This combo gives you the deep rumble when you step on it, but stays civil when you're just commuting to work.
Final Thoughts
At the end of the day, installing frs unequal length headers is about making the car yours. If you want the most efficient, track-ready machine possible, go with equal length. But if you want a car that puts a smile on your face every time you start it up in the morning, UEL is the way to go.
It fixes the power delivery, it cuts weight, and it finally gives the FRS the "soul" it was missing from the factory. Just remember: buy quality parts, don't skimp on the gaskets, and for the love of all things mechanical, get a tune. Your ears (and your engine) will thank you.