COMP Cams CL51-601-11 Mutha' Thumpr 235/249 Hydraulic Roller Cam & Lifter Kit for Pontiac 265-455

The COMP Cams CL51-601-11 Mutha' Thumpr Hydraulic Roller Cam and Lifter Kit is a high-performance street/strip camshaft solution engineered for Pontiac 265-455 cubic inch engines. Built on COMP's legendary Thumpr platform, this billet steel hydraulic roller camshaft delivers the aggressive, loping idle sound enthusiasts crave while producing real gains in horsepower and torque across a broad RPM range.

The Mutha' Thumpr grind is the middle step in COMP's three-cam Thumpr lineup — stepping up from the Thumpr and below the Big Mutha' Thumpr — making it ideal for performance builds that demand a noticeable exhaust note and strong street/strip output. Early intake valve opening combined with long exhaust duration creates substantial overlap, producing a hard-hitting exhaust note and improved high-RPM performance. This cam is best paired with an aftermarket torque converter, performance intake, headers, and numerically higher rear gear ratios.

Camshaft Specifications:

• Grind Number: 291THR7
• Cam Type: Hydraulic Roller
• Camshaft Material: Billet Steel
• Intake Duration @ .050": 235°
• Exhaust Duration @ .050": 249°
• Advertised Intake Duration: 291°
• Advertised Exhaust Duration: 311°
• Lobe Separation Angle: 107°
• Intake Valve Lift: 0.522"
• Exhaust Valve Lift: 0.508"
• Basic Operating RPM Range: 2,000–5,800
• Camshaft Gear Attachment: 1-Bolt

Kit Contents (CL-Kit):

• Mutha' Thumpr hydraulic roller camshaft
• Hydraulic roller lifters
• Assembly lubricant
• COMP Cams decals
• Installation instructions

Important Build Notes:

• Requires minimum 9:1 compression ratio
• Requires 2,500+ RPM stall speed torque converter
• Requires performance intake manifold, headers, and rear gearing
• Valve springs upgrade required — not included
• Produces a rough, lopey idle characteristic of the Thumpr grind

For a more complete valvetrain solution, upgrade to the K51-601-11 K-Kit, which adds a timing set, valve springs, retainers, locks, and seals. California Proposition 65 Warning: This product can expose you to chemicals known to the State of California to cause cancer and reproductive harm. See P65Warnings.ca.gov.