The engine is the heart of an HPA rifle — the component that fires the BB. Drop-in conversion kits for AEGs, or standalone units for purpose-built HPA platforms.

An HPA engine replaces the mechanical gearbox of a traditional AEG with a pneumatic firing system: a piston driven by compressed air rather than a motor-driven spring. The result is instant trigger response, no mechanical wear cycle, and electronic configurability — the things that make HPA fundamentally different to AEG rather than just an upgrade path.

Drop-in AEG conversions are engines designed to fit into an existing AEG gearbox shell — Wolverine INFERNO Gen 2 (V2 for M4-pattern, V3 for AK-pattern), Wolverine REAPER (modern open-bolt engine), and PolarStar Jack/F2/F1 are the established options. These let you keep your AEG's receiver, stock, and outer barrel while swapping the firing system to HPA. Our AEG to HPA conversion guide walks through which engine fits which rifle.

Standalone HPA engines are sold for purpose-built HPA platforms like the Wolverine MTW and Article series — these aren't conversion kits, they're replacement units for rifles that were always HPA. The INFERNO XTS is the current high-end engine; older MTW engines can be upgraded if yours is showing wear. Engines need an FCU and regulator matched to them — most ship with the FCU integrated; some need it ordered separately. The HPA tech service covers installation if you'd rather not strip the rifle yourself.

💡 Titan Forge tip: If you're converting an AEG, check your gearbox version first (V2 for most M4s, V3 for AKs, V6 for Thompson and a few others) — the engine has to match the gearbox shell exactly. Call us on 01494 911990 with your rifle's model and we'll confirm compatibility.