SKU: KB-050-EJ-S
Kartboy Aluminum Crank Pulley EJ Engines – Alternator Belt with A/C Pump Delete
The Kartboy KB-050-EJ-S Aluminum Crank Pulley is the best lightweight underdrive pulley upgrade for Subaru EJ engines (EJ20/EJ25) with alternator belt drive and A/C pump delete setups. CNC-machined from high-grade billet aluminum, this pulley reduces rotational mass for quicker throttle response, faster revs, and small horsepower/torque gains while eliminating the A/C compressor load – ideal for track-focused WRX/STI, Legacy GT, Forester XT, or any EJ-series build where maximum performance and reduced parasitic drag matter, without retaining air conditioning.
Key Features
- Lightweight Billet Aluminum: Significantly reduces rotational inertia over stock pulley – quicker engine response
- A/C Pump Delete Design: Eliminates A/C compressor belt load for freed-up horsepower and cleaner engine bay
- Alternator Belt Compatible: Maintains alternator function with dedicated belt path – no electrical issues
- Precision CNC Machining: Perfect balance and fitment anodized finish for corrosion resistance and style
- Direct Bolt-On Fit: Uses factory crank bolt and timing marks no modifications required
- Kartboy Quality: Trusted Subaru performance brand reliable for street and track EJ builds
Specifications
| Specification | Detail |
|---|---|
| Part Number | KB-050-EJ-S |
| Material | Billet Aluminum |
| Finish | Anodized (Silver / Black Options) |
| Compatibility | Subaru EJ Engines (EJ20/EJ25) with Alternator Belt & A/C Delete |
| Installation | Direct Bolt-On (Uses Factory Crank Bolt) |
| Country of Origin | United States |
| Warranty | Limited (Kartboy) |
| Shipping Weight | Approx. 2-3 lbs |
Product Notes
- A/C delete pulley – removes compressor load for performance gains (A/C no longer functional)
- Underdrive design frees up horsepower noticeable throttle response improvement
- Recommended for track, autocross, or high-performance street builds not for daily A/C use
Installation Notes
- Estimated time: 1-2 hours, moderate difficulty, basic hand tools required
- Remove stock pulley, install Kartboy pulley with factory bolt, torque to spec, reroute alternator belt
- Professional installation recommended check timing marks and belt tension
This Part Fits
| Year | Make | Model | Notes |
|---|---|---|---|
| 1992-2021 | Subaru | Impreza WRX / WRX STI | EJ20 / EJ25 Engines (A/C Delete Setup) |
| 2004-2009 | Subaru | Legacy GT / Outback XT | EJ255 / EJ257 Engines (A/C Delete) |
| 2003-2014 | Subaru | Forester XT | EJ25 Turbo Engines (A/C Delete) |
| Various | Subaru | EJ Series Swaps | Custom Turbo & Performance Builds |
Why Choose Kartboy Aluminum Crank Pulley?
- Lightweight billet design reduces rotational mass quicker revs and throttle response
- A/C delete frees up horsepower ideal for track or performance EJ builds
- Limited warranty trusted Subaru-specific upgrade from Kartboy
Frequently Asked Questions
- Q: Will this pulley fit my 2015 Subaru WRX STI EJ257?
A: Yes, Kartboy KB-050-EJ-S fits all Subaru EJ20/EJ25 engines with alternator belt and A/C delete setup. - Q: Does it eliminate A/C completely?
A: Yes, designed for A/C pump delete; air conditioning will no longer function. - Q: How much power gain?
A: Small gains (5-10 whp typical) from reduced parasitic drag most noticeable in throttle response. - Q: What is the warranty?
A: Covered by Kartboy limited warranty built for performance.
Shipping & Handling
- Method: UPS/FedEx Ground
- Availability: In stock – ships same or next business day
- Packaging: Secure protective packaging
- Weight: Approx. 2-3 lbs
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