ATI 917991 Super Damper Harmonic Balancer for 1998-2021 Subaru WRX STI EJ20/EJ22

Vehicle Fitment

• 2002-2005 Subaru Impreza WRX 2.0L EJ205
• 2004-2021 Subaru Impreza WRX STI 2.5L EJ257

Fitment Notes

• Direct replacement for stock OEM crank damper
• 5.5" outer diameter -- 5% overdriven pulley
• 4-groove and 5-groove serpentine belt drive, uses factory serpentine setup
• SFI 18.1 certified, approved for competition use

Features

• Patented Super Damper design -- two dampers in one, 4" inner + larger outer damper
• Eliminates torsional crankshaft vibrations at all RPM levels
• Proven elastomer tuned to eliminate harmful crankshaft harmonics
• Reduces parasitic horsepower loss from crankshaft harmonics
• Tunable in the field and fully rebuildable
• Laser-etched 360-degree timing marks
• Exceeds SFI 18.1 safety specifications
• Black zinc chromate finish
• Computer-machined grooves retain proper durometer O-rings, dyno tested per application

Specifications

• Outer diameter: 5.5"
• Inner diameter: 4"
• Engine balance: Internal
• Material: Aluminum
• Finish: Black zinc chromate
• SFI rating: SFI 18.1
• Belt grooves: 4-groove and 5-groove serpentine
• Degree markings: Yes, laser engraved

Included Components

• 1x Super Damper crank pulley (hub, outer shell, inertia ring)
• 1x Bolt kit

Product Description

The ATI 917991 Super Damper is a 5.5" crank pulley built as a direct replacement for the OEM crank damper on the Subaru WRX and WRX STI, engineered specifically for high-RPM engines that push past factory design limits. Unlike undampened underdrive pulleys, which offer zero protection to a high-performance engine, this Super Damper provides genuine balanced dampening of torsional crankshaft vibrations at every RPM level.

The factory crank damper is a wear item -- its rubber components deteriorate over time and can eventually fail, in worst cases allowing pistons to contact valves and destroy the engine entirely. Factory dampers were also never designed for the higher RPM many owners run when modifying their WRX or STI. ATI's patented design is actually two dampers in one: a 4" inner damper paired with a larger outer damper in dual shells that bolt to the crank hub, working together to all but eliminate worn parts and timing problems.

Tunable in the field and fully rebuildable, this damper exceeds SFI 18.1 safety certification and is approved for competition use -- many sanctioned race classes require an SFI-approved crank pulley and won't pass a factory damper through tech inspection. Laser-etched timing marks and a durable black zinc chromate finish round out a damper built to protect a high-performance EJ20/EJ25 engine at every RPM, whether on the street or on track.