Improved Racing LS Billet Rear Passage Plug — GM Gen III/IV Barbell, CNC 6061-T6, Dual O-Ring Seal

Improved Racing's billet rear passage plug is a direct-fit replacement for the plastic GM barbell plug on Gen III & IV LS engines, engineered to stop unfiltered oil bypass and restore correct oil routing.

Older or factory plastic rear passage plugs in GM LS-series engines can deform, crack, or allow oil to bypass the filter. This billet aluminum oil diverter — commonly called a "barbell" plug — replaces the OEM plastic plug with a precision-machined part that seals the gallery and channels oil through the filter housing as intended. It’s a compact upgrade that addresses oil-flow integrity without modifying the engine block or oiling system.

How does this plug prevent dirty oil from bypassing the filter?

The Improved Racing plug uses a dual O-ring sealing arrangement and a precisely machined profile to close off the rear oil passage. That positive seal blocks the route that allows unfiltered oil to shortcut past the filter media, keeping contaminants in the filter where they belong.

• Double O-ring design for two-stage sealing
• Accurate internal geometry to guide oil through the filter housing
• Replaces failure-prone plastic OEM barbells

Is this a straight swap for GM Gen III & IV LS engines?

Yes — the part is made to match the OEM dimensions and function so it installs in place of the factory plastic barbell plug. No block machining or adapter is required; installation uses the existing gallery opening and threads for a clean, direct fit.

• Direct replacement for GM LS Gen III and IV rear barbell plug
• M4x0.7 threaded removal hole for easy extraction if needed
• Form-fit to factory gallery to maintain original oil routing

What materials and manufacturing processes are used?

The plug is CNC-machined from 6061-T6 aluminum for strength, dimensional accuracy, and corrosion resistance. Viton O-rings provide durable sealing against hot engine oil, and the part is manufactured domestically to consistent quality standards.

• Precision CNC-machined from billet 6061-T6 aluminum
• Viton O-rings for long-lasting oil resistance
• Made in the USA for traceable manufacturing quality

How do I remove or service the plug if it’s stuck?

The plug includes a small threaded M4x0.7 port designed specifically to help removal. You can install a suitable extraction tool or screw to back the plug out without damaging the block, reducing the risk of seized or broken OEM plastic pieces.

• M4x0.7 threaded hole accepts removal tool or bolt
• Billet construction resists distortion during extraction attempts
• Reduces chance of leaving broken plastic in the oil gallery

Who is this for: Owners and builders of GM LS Gen III and IV engines who want a reliable, long-lasting replacement for the fragile OEM plastic rear barbell plug. It’s ideal for performance builds, routine maintenance upgrades, and any application where preserving proper oil circulation and filtering is a priority. If you value durable materials, positive sealing, and a simple direct-swap installation, this billet oil diverter plug is a practical upgrade.