HKS Legamax Premium Cat Back Exhaust System

2015+ WRX / 2015+ STI

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SKU: 31021-BF001We price match!

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Legamax and Sport Exhaust Systems are designed to reduce backpressure and increase exhaust flow for greater peak power and a broader torque band.
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Legamax and Sport Exhaust Systems are designed to reduce backpressure and increase exhaust flow for greater peak power and a broader torque band. Each Legamax and Sport Exhaust application utilizes a specific muffler design and shape along with the appropriate piping diameter to maintain low-end torque while maximizing high-end horsepower. All Legamax systems are made from polished SUS304 stainless steel piping.


  • 3" to split 2.4" piping
  • Four 3.54" exhaust tips
  • 83dB vs stock 82dB (stock STI)

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3 customer reviews

Average rating
(based on 3 reviews)
Ease of Installation
Fit / Quality
Overall Satisfaction
  1. Probably the best low noise catback.

    By krolsky June 10, 2022

    - Installation and fit was great. It took around 1 hour to remove the stock exhaust and only 15 minutes to install the HKS. If you're lifting just the rear like I did, you need to max out your jacks to fit behind the cat. Secure the car with good jack stands as well. - The quality of the stainless steel and the welds is astounding. - It looks beatiful, the pipes hang high as compared to the COBB which has them hanging way too low for no reason, just google some rear photos. I'm talking about the Y pipe mainly. My only gripe; I wish the tips were double wall and more slanted like most of the competition. The tips are nice, but from the rear they're barely visible due to thin wall. I also dislike the bright reflection you get from the mufflers but that seems to be common with all exhausts of this kind. I'm considering painting the cans matte black for a cleaner look. - Now the sound. Drake JDM on YTube has a good recording, the one with audio only. It sounds just like that. It's a great sound profile; it purrs, is louder than stock by about 15%, it's lower tone. It sounds amazing when doing higher rpm pulls. In fact, that's the best part, it's so addictive. Only downside is the exhaust is quite boomy, around the same low rpm where the stock pipe was boomy, except now it's 10-15% louder. So in slow traffic, or indoor parking lots it gets a bit loud, so that's the tradeoff. If you want to hear it compared to others, and see specs, dsportmag did a reallt good comparison. Overall, it's an improvement over stock. Quieter than the other catbacks. You're probably thinking, what about the Q300? Well, the Q300 sounds very similar but has tips so large you can fist them. In lots of videos it also appears more bassy, which may be overkill. The HKS has just a bit of rasp to it, which sounds more natural. - I did not notice any power gains in my butt dyno. There may be a few hp and lbs here and there but it's hard to tell.

  2. If you're looking for a quiet cat-back system this is it!

    By Aaron July 17, 2019

    Just installed on my 2018 STI, everything needed for the install was included, exhaust looks, and fits great. Install was very easy, only took me about 20 min. Overall the exhaust is quiet as stock at idle, with the sound level picking up to about 10 DB louder around 1200 rpm and maintains that slightly louder tone throughout the rev range.

  3. Great System!!

    By Steve June 3, 2017

    I love this exhaust! With stock cat its actually quieter then stock at Idle it does get 'louder' and sound amazing when you floor it!

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