Next Level Performance
August 15, 2026 • 9 min read
Our Verdict
The HKS Super Turbo Muffler Ti is the halo cat-back for the 2015-2021 WRX STI — full titanium, feather-light, and unmistakably HKS.
At around $6,300 it is the most expensive exhaust in this guide by a wide margin, but no stainless system matches its weight savings, heat tolerance, or that signature large-bore Super Turbo Muffler tone. If your budget is tighter, the Borla S-Type and Invidia Gemini deliver most of the drama for roughly a third of the price.
Shop Our Top Pick →The HKS Super Turbo Muffler Ti is a full-titanium cat-back exhaust built for the 2015-2021 Subaru WRX STI (VAB chassis) that strips weight, survives serious heat, and delivers HKS's signature large-diameter tone. It sits at the top of the WRX STI cat-back exhaust market at roughly $6,300, and in this review we put it head-to-head with four proven stainless-steel alternatives — the Borla S-Type, HKS Hi-Power SPEC-L2, Invidia Gemini/R400, and MagnaFlow Competition Series — so you can decide whether titanium is worth the premium on your EJ25. At NLP Performance in Tampa, FL, the VA-chassis STI is one of the most common cars on our lift, and exhaust is the first mod most owners ask about.
What Is the HKS Super Turbo Muffler Ti?
The HKS Super Turbo Muffler Ti is HKS's flagship titanium exhaust for the VAB-generation Subaru WRX STI, using a single oversized tip and lightweight titanium construction to cut weight while producing a deep, tuned exhaust note. Titanium has a density of roughly 4.5 g/cm3 versus about 7.9 g/cm3 for stainless steel, so a titanium system can weigh close to 40 percent less than a comparable T-304 stainless cat-back. On a nose-heavy, all-wheel-drive STI, shedding weight at the very back of the car is a real handling benefit, not just a spec-sheet flex.
HKS designed the Super Turbo Muffler line around a large-bore single-canister layout tuned to reduce backpressure on turbocharged engines while keeping drone manageable at highway cruise. On the EJ25, the payoff is a fuller mid-range and a distinctive burnt-titanium tip that has become an instantly recognizable JDM signature. It fits 2015-2021 WRX STI models and, like most large-bore performance exhausts, it is a non-CARB (off-road / competition) part — something to confirm against your state's emissions rules before you buy.
Key Specifications
The Super Turbo Muffler Ti's signature large single titanium tip.
How Does It Sound and Perform on the VA STI?
On a stock-turbo EJ25, a cat-back exhaust like the HKS Super Turbo Muffler Ti is primarily a sound, weight, and flow upgrade rather than a big-horsepower part. Cat-back-only changes on the VA STI typically free up somewhere in the low single digits to around 8-10 wheel horsepower, with the largest gains arriving once you pair the exhaust with a high-flow downpipe and a Stage 2 tune. The titanium system's real advantages are the weight it removes behind the rear axle and the way it holds up to repeated heat cycling far better than mild steel.
Tonally, the Super Turbo Muffler Ti trades the classic boxer rumble for a cleaner, higher-pitched HKS growl with a hard-edged top end — it is noticeably more aggressive than a quiet OE-style system but tuned to avoid the worst of the highway drone that plagues cheaper straight-through mufflers. Subaru owners consistently describe the large-bore HKS note as louder under throttle yet livable on a daily commute. If you want the most raucous, in-your-face quad-tip sound, the Invidia Gemini and MagnaFlow Competition go harder; if you want refined and restrained, HKS's own Hi-Power SPEC-L2 is the calmer choice.
Why Upgrade the Factory WRX STI Exhaust?
The factory 2015-2021 WRX STI cat-back is heavy, restrictive, and deliberately muted. The OE system uses smaller-diameter piping and dense mufflers to meet strict drive-by noise limits, which chokes flow and adds weight low and rearward on the chassis. Swapping to a 3-inch aftermarket cat-back like the Borla S-Type or MagnaFlow Competition — or a full-titanium HKS Super Turbo Muffler Ti — opens the exhaust path, drops several pounds, and unlocks the boxer character Subaru muffles from the factory.
There are three practical reasons STI owners in our Tampa shop upgrade first: sound, weight, and future-proofing. A cat-back transforms the car's voice immediately, removes anywhere from a few pounds (stainless) to close to 40 percent of the system weight (titanium), and lays the groundwork for a downpipe and Stage 2 tune later. Because a cat-back does not touch the catalytic converter or any pre-turbo sensor, it also will not throw a check-engine light or require a retune on its own — making it the safest, most reversible first modification on the EJ25.
HKS Super Turbo Muffler Ti vs the Best WRX STI Cat-Backs
Below is how the titanium HKS stacks up against four of the most popular cat-back exhausts we install on the 2015-2021 WRX STI. We compared the attributes buyers ask about most — material, tip configuration, and sound character — alongside current pricing. The HKS is the outlier on price, but it is also the only full-titanium option here.
| Kit | Material | Tip Setup | Sound | Price |
|---|---|---|---|---|
| HKS Super Turbo Muffler TiTop Pick | Titanium | Single large-bore | Aggressive, refined | $6,300.00 |
| Borla S-Type Cat-Back | T-304 stainless | Dual 2.5in black chrome | Aggressive | $1,949.99 |
| HKS Hi-Power SPEC-L2 | Stainless steel | Single tip | Moderate, street | $1,800.00 |
| Invidia Gemini/R400 | 304 stainless | Quad black tips | Aggressive | $1,588.36 |
| MagnaFlow Competition | Stainless steel | Quad 4in polished | Deep, loud | $1,413.00 |
Borla S-Type — Best Stainless Value
The Borla S-Type is our go-to when a customer wants an aggressive, name-brand cat-back without spending titanium money. It is built from premium T-304 stainless steel with 3-inch mandrel-bent piping and Borla's patented multi-core straight-through technology, capped by 2.5-inch black chrome tips. Borla backs it with a Million-Mile Warranty — the strongest coverage in this comparison — and it currently runs around $1,950, down from $2,183.99.
Borla's T-304 stainless S-Type with 3-inch mandrel bends.
HKS Hi-Power SPEC-L2 — The Quiet HKS
If you like the HKS name but want a calmer daily driver, the Hi-Power SPEC-L2 is the answer. It is HKS's street-focused, single-tip stainless system engineered to keep interior drone in check while still adding a sportier note than stock. At $1,800 it is far more attainable than the titanium Super Turbo Muffler and fits 2015-2021 WRX and WRX STI models.
Invidia Gemini/R400 — Best Aggressive Look
The Invidia Gemini/R400 delivers the quad-tip, blacked-out look most VA STI owners picture when they imagine an exhaust upgrade, and it is the value champion here. Built from 304 stainless in a single-layer design with black quad tips, it currently sells for about $1,588 — a steep drop from its $2,406.60 list price. It fits 2015-2022 WRX and STI models and brings a loud, N1-style bark under boost.
Invidia's blacked-out quad tips are the value look leader.
MagnaFlow Competition Series — Deepest Note
The MagnaFlow Competition Series 19361 is the budget pick and the loudest, deepest-sounding system in this guide. It uses 3-inch mandrel-bent stainless piping with straight-through mufflers and a quad split-rear exit finished with 4-inch polished double-wall tips. MagnaFlow backs it with a lifetime warranty, and at $1,413 it is the least expensive cat-back we recommend for the 2015-2017 WRX STI.
MagnaFlow's quad 4-inch polished tips and straight-through mufflers.
HKS Super Turbo Muffler Ti: Pros and Cons
What We Like
- + Full titanium construction, roughly 40 percent lighter than stainless
- + Signature large-bore HKS tone with controlled highway drone
- + Excellent heat tolerance and corrosion resistance
- + Instantly recognizable burnt-titanium single tip
Things to Consider
- – Roughly triple the price of top stainless systems
- – Non-CARB / off-road part — check local emissions laws
- – Cat-back alone adds only modest peak power without a tune
Installation and Fitment Notes
Every exhaust in this guide is a direct bolt-on cat-back for the VA-chassis Subaru WRX STI and installs in roughly 1 to 2 hours with basic hand tools, a set of jack stands, and fresh gaskets. Because these are cat-back systems, they connect at the factory downpipe/mid-pipe flange and leave the catalytic converter in place. Confirm your exact fitment window before ordering: the HKS Super Turbo Muffler Ti and Hi-Power SPEC-L2 cover 2015-2021, the Borla S-Type covers 2015-2019, the Invidia Gemini/R400 covers 2015-2022, and the MagnaFlow Competition Series is listed for 2015-2017.
A quick tip from our Tampa shop: soak the OE exhaust hangers and flange bolts with penetrating oil before you start, and swap the rubber isolators if they are cracked. If you plan to chase real power, budget for a high-flow downpipe and a Stage 2 tune at the same time — that is where the STI's EJ25 wakes up, and it lets any of these cat-backs breathe to their potential. Browse the full range in our exhaust systems collection.
Which WRX STI Cat-Back Should You Buy?
Choose the HKS Super Turbo Muffler Ti ($6,300) if you want the ultimate weight savings, titanium durability, and the halo HKS tone, and the price premium does not scare you. For the best balance of aggression, brand pedigree, and warranty, the Borla S-Type ($1,949.99, backed by a Million-Mile Warranty) is the smart-money pick. Want the meanest quad-tip look for the least cash? The Invidia Gemini/R400 ($1,588.36) is unbeatable value. Prefer the deepest, loudest note on a budget? The MagnaFlow Competition Series ($1,413, lifetime warranty) delivers. And if you love HKS but daily-drive with passengers, the quieter Hi-Power SPEC-L2 ($1,800) keeps the drone down. Every one of these is in stock and ships from NLP Performance in Tampa, FL.
Frequently Asked Questions
Is the HKS Super Turbo Muffler Ti worth it for a WRX STI?
The HKS Super Turbo Muffler Ti is worth it if you want the lightest, most heat-resistant cat-back and the signature HKS titanium tone, and price is a secondary concern. At around $6,300 it costs roughly three times a premium stainless system like the Borla S-Type, so most daily-driven STIs are better served by stainless unless weight savings and titanium prestige matter to you.
How much horsepower does a cat-back add to a 2015-2021 WRX STI?
A cat-back exhaust alone typically adds only a few wheel horsepower to a stock-turbo WRX STI — commonly in the low single digits up to about 8-10 whp. The real gains come from pairing the cat-back with a high-flow downpipe and a Stage 2 tune, which together can add 40-plus whp on the EJ25.
Is titanium exhaust better than stainless steel on an STI?
Titanium is better for weight and heat resistance: it is roughly 40 percent lighter than T-304 stainless and tolerates higher exhaust temperatures. Stainless steel is far cheaper, still highly corrosion-resistant, and offers plenty of aftermarket sound and flow options, which is why most STI owners choose stainless cat-backs like the Borla, Invidia, or MagnaFlow.
Which WRX STI cat-back is the loudest?
Among these five, the MagnaFlow Competition Series and Invidia Gemini/R400 are the loudest and most aggressive thanks to straight-through mufflers and quad-tip layouts. The HKS Hi-Power SPEC-L2 is the quietest and most street-friendly, while the HKS Super Turbo Muffler Ti and Borla S-Type sit in the aggressive-but-refined middle.
Are these cat-back exhausts legal for the street?
Cat-back exhausts leave the catalytic converter in place, so they do not remove emissions equipment. However, large-bore performance systems like the HKS Super Turbo Muffler Ti are labeled non-CARB (off-road/competition) and may not meet noise or emissions rules in every state. Always confirm your local laws before purchase.
Do I need a tune after installing a cat-back on my STI?
No, a cat-back exhaust does not require a tune to run safely because it does not change airflow before the turbo or affect the factory sensors. A tune is only necessary if you also add a high-flow downpipe or other airflow mods, at which point retuning is strongly recommended to maximize power and keep the engine safe.
Ready to Upgrade Your STI's Exhaust?
Shop the HKS Super Turbo Muffler Ti and every cat-back in this guide at NLP Performance.
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