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K&N E-3988 is a washable reusable oval air filter designed as a direct replacement for RK Series air cleaner assemblies on Harley-Davidson Sportster motorcycles from 2004 to 2022. This high-flow filter increases horsepower and acceleration by allowing greater airflow while maintaining strong filtration to protect your engine. Crafted with cotton gauze media and precise dimensions of 9.313in outer diameter 8.25in inner diameter and 2.375in height it fits perfectly in RK-3930 RK-3113 and compatible assemblies.
Key Features
- Precise Fit Specifications: Oval shape with 9.313in flange OD 8.25in flange ID 2.375in height and centered rubber flanges drops into RK Series assemblies without modifications.
- Weight: 1.2 lb (0.5 kg).
- High Airflow Design: Boosts horsepower and rate of acceleration through increased air volume for responsive throttle and quicker rides on Sportster models.
- Ships in protective box measuring 9.45in x 9.21in x 3.98in.
Fitment
| Fitment Status | Universal or dimensional product |
|---|---|
| Required Verification | Exact dimensions, media, connection, mounting interface, and companion part number |
Specifications
| Brand | K&N Engineering |
|---|---|
| Manufacturer Part Number | E-3988 |
| Product Type | Air Filters - Direct Fit |
| Fitment Type | Universal |
| Condition | New |
What's Included
One new K&N air filters - direct fit identified by manufacturer part number E-3988. Hardware, adapters, clamps, hoses, filters, and service supplies are included only when stated for this exact product.
About K&N Engineering
K&N develops reusable air filtration, intake, oil filtration, fuel filtration, and related performance products for vehicle-specific and dimensional applications.
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Frequently Asked Questions
How do I confirm K&N E-3988 fits my setup?
Match every listed dimension, flange or thread size, media type, mounting interface, and companion component. A similar shape or outside dimension alone does not confirm compatibility.
Is K&N E-3988 washable and reusable?
Serviceability depends on the exact media used for this part number. Follow the K&N cleaning and oiling directions for this filter and never apply oil to media specified as dry.
What should be checked after installing K&N E-3988?
Verify seals, clamps, fasteners, hoses, sensors, wiring, and surrounding clearance as applicable. Check for leaks or contact, then follow the manufacturer service and reinspection schedule.
Installation Instructions
- Remove old filter from RK Series housing and insert E-3988 directly no tools required for most setups.
- Compatible with stock RK backing plates and hardware on Sportster models.
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