Invidia HS11STIGM4SS Gemini R400 Quad Cat-Back for 2008-2014 WRX 2011-2014 STI

Vehicle Fitment

• 2008-2014 Subaru WRX Sedan (GR | EJ255 2.5L Turbo)
• 2011-2014 Subaru WRX STI Sedan (GR | EJ257 2.5L Turbo)

Fitment Notes

• Compatible with the GR-generation Subaru WRX Sedan across all trim levels (Base, Premium, Limited) for model years 2008-2014, and WRX STI Sedan for 2011-2014.
• Sedan body style only. This part will NOT fit the WRX or STI hatchback - hatchback models use a different exhaust routing and require a separate application-specific part.
• If retaining the factory stock J-pipe or downpipe, a stock downpipe to 3" cat-back adapter is required for proper fitment. The recommended adapter is GrimmSpeed p/n 077046. Aftermarket 3" downpipes typically connect directly without an adapter.
• This is a cat-back exhaust system - it connects at the downpipe/midpipe and replaces all piping, mufflers, and tips rearward. The factory catalytic converter is retained, making this system 50-state emissions legal.
• Does not fit the 2015+ WRX/STI (VA chassis), which uses a different exhaust configuration. For that application, see Invidia HS15STIGM4SS.
• Available with polished straight-cut stainless steel tips (HS11STIGM4SS - this part) or burnt titanium tips (HS11STIGM4ST).

Features

• R400 tuned muffler design - four separate single-layer canister mufflers are optimized specifically to fill the sound character gap between the Q300 and N1 systems: more aggressive and throaty than the Q300's muted tone, but without the N1's unfiltered harshness during highway cruising
• The R400's quad muffler configuration enhances the EJ25 boxer engine's characteristic low-frequency rumble and produces an authoritative, deep exhaust note throughout the entire RPM band - particularly strong in the mid-range where the EJ255/EJ257 builds boost
• 76mm (3") SUS304 stainless steel mandrel-bent piping with a minimal-bends design philosophy dramatically reduces the back pressure created by the factory exhaust system's smaller diameter and press-bent routing, enabling improved mid-to-top-end power and improved throttle response
• 1.5mm thick stainless steel piping construction greatly reduces the risk of cracking and stress fractures that affect thinner-walled aftermarket exhausts - providing long-term structural integrity on a platform known for turbo-generated thermal cycling
• Quad 101mm (4") polished straight-cut stainless steel tips provide a bold, symmetrical visual statement at the WRX/STI sedan's rear bumper - filling the bumper cutout with a purposeful, race-inspired quad exit that is instantly recognizable in the Subaru community
• Cast CNC machined flanges at all connection points ensure precision fitment and long-term leak-free sealing - superior to stamped flanges for thermal expansion resistance
• Invidia's minimal-bends design routing keeps the piping as straight as physically possible within the sedan's underbody geometry, minimizing turbulence at every directional change for the most unobstructed exhaust flow path achievable as a bolt-on cat-back
• 50-state emissions legal - connects after the factory catalytic converters, which are retained
• New gaskets and all necessary hardware included for a complete installation
• Manufactured in Japan by Invidia to the highest production standards
• Covered by Invidia's 1-year manufacturer warranty against defects in material and workmanship

Specifications

• Part Number: HS11STIGM4SS
• Brand: Invidia
• Series: Gemini R400
• System Type: Cat-Back
• Application: 2008-2014 Subaru WRX Sedan (GR) | 2011-2014 Subaru WRX STI Sedan (GR) - Sedan Only
• Piping Material: SUS304 Stainless Steel
• Piping Wall Thickness: 1.5mm
• Piping Construction: Mandrel-Bent, Minimal Bends Design
• Main Piping Diameter: 76mm (3")
• Muffler Style: R400 Single-Layer Tuned Canisters
• Muffler Quantity: 4 (Quad)
• Exit Configuration: Quad Rear Exit
• Tip Material: Stainless Steel
• Tip Finish: Polished
• Tip Shape: Straight-Cut Round
• Tip Diameter: 101mm (4")
• Tip Quantity: 4
• Flange Type: Cast CNC Machined
• Hardware: New gaskets and hardware included
• Emissions: 50-State Legal (cat-back, retains factory catalytic converters)
• Stock DP Adapter Required: Yes - GrimmSpeed p/n 077046 (if retaining factory stock downpipe)
• Warranty: 1-Year Manufacturer Warranty
• Made in Japan

Included Components

• 1x Mandrel-Bent 304 SS Front Midpipe Section (76mm)
• 4x R400 Single-Layer Tuned Muffler Canisters with Quad 101mm Polished Straight-Cut Stainless Steel Tips
• New Gaskets and Complete Hardware Kit
• Installation Instructions
• Note: GrimmSpeed stock DP adapter (p/n 077046) required if retaining factory downpipe - sold separately

Product Description

The Invidia HS11STIGM4SS is a Gemini R400 series cat-back exhaust system designed specifically for the 2008-2014 Subaru WRX Sedan and 2011-2014 WRX STI Sedan (GR chassis). It features 76mm mandrel-bent SUS304 stainless steel piping, four individual R400 single-layer tuned muffler canisters, and quad 101mm polished straight-cut stainless steel tips - one of the most distinctive and well-regarded cat-back exhaust configurations available for the GR-generation WRX/STI platform. Sedan body style only; will not fit hatchback models. 50-state emissions legal as a cat-back system that retains the factory catalytic converters.

The R400's defining characteristic is its four-canister quad muffler architecture. Where conventional cat-back systems use one or two muffler canisters, the R400 routes each of the WRX/STI's exhaust paths through dedicated R400 tuned canisters - four total - that are individually calibrated to produce Invidia's target sound character. The result is a sound profile that sits deliberately between the Q300's reserved tone and the N1's aggressive straight-through character. The R400 delivers a deep, authoritative boxer rumble at low RPM and idle that builds to an aggressive exhaust note under wide-open throttle acceleration, without the resonance and cabin drone that makes louder systems fatiguing on long highway runs. For GR WRX/STI owners who want genuine presence and sound character without sacrificing daily drivability, the R400 occupies a well-established position as the benchmark cat-back for this platform.

The 76mm, 1.5mm-thick piping with minimal bends addresses the factory exhaust's back-pressure restrictions across the mid-to-top-end power range, delivering dyno-proven horsepower and torque improvements. Owners retaining the factory stock J-pipe or downpipe will need the GrimmSpeed stock downpipe to 3" cat-back adapter (p/n 077046) for proper fitment - aftermarket 3" downpipes connect directly. Manufactured in Japan and covered by Invidia's 1-year manufacturer warranty.