Big Valve 37.5/32mm Cylinder Head for GX390, Predator 420 & Clone Engines

EC Big Valve Performance Cylinder Head for GX390, Predator 420, Wildcat 460 & Big Block Clones

Unlock the full potential of your big block clone engine with EC’s Big Valve Cylinder Head, engineered to deliver superior airflow, increased power, and reliable high-RPM performance. Designed to fit Honda GX390, Predator 420/459, Wildcat 460, and other 420cc+ clone engines, this head is a must-have upgrade for serious performance builders.

Recognizing that real power starts in the cylinder head, EC set out to create a high-flow cast head tailored for engines running aggressive camshafts, high-ratio rockers, and stronger valve springs. The result is a precision-machined wedge-style cylinder head with oversized valves and a valvetrain setup built to handle up to .420” lift.

Performance Features & Benefits

• Oversized Valves for Maximum Flow
• 37.5mm intake & 32mm exhaust dramatically improve airflow
• 6.5mm Valve Stems with 6mm Tips
• Allows use of EC’s lightweight 6mm titanium retainers and locks
• Performance-Spec Valve Springs Included
• Handles up to .420” cam lift
• Pre-installed for easy bolt-on installation

Fitment Note: This head uses a standard wedge-style 420cc head design with a single valve cover bolt. Make sure you have the correct valve cover and hardware before purchasing.

Valve Spring Specs (Installed)

• Install Height: 1.150"
• Seat Pressure (Closed): 70 lbs
• Open Pressure at .730" (.420 Lift): 147 lbs
• Coil Bind: 0.690"

Why Choose the EC Big Valve Head?

The stock cylinder head quickly becomes a bottleneck once performance parts like cams and high-ratio rockers are added. EC’s Big Valve Head removes that restriction, offering:

• Greater airflow for better combustion and torque
• Compatibility with high-lift camshafts
• Reliability under extreme RPM conditions
• Drop-in fit for most big block clone engines