LS3 255cc 4.000" (+) Bore - Pair Black Label CNC Cylinder Head

---->Download the cylinder head spec sheet<---- The Mast Motorsports cylinder head product line is completely manufactured from a raw casting to a finished cylinder head in the USA located in Nacogdoches Texas.  Mast refuses to compromise on materials and methods that may jeopardize longevity, performance, and quality. When buying Mast Cylinder heads, you are getting the highest level of quality and performance on the market.  Full Send, no compromises, no shortcuts, ever. Dimensional Specs Bore Size: 4.000" (+) Weight: 28 lbs. Intake Valve Size: 2.165" Exhaust Valve Size: 1.600" Valve Stem Diameter: 5/16" Valve Length: 5.450" Valve Angle: 11° Valve Spring Pocket Diameter: 1.65" Valve Spring Install Height: 1.800" Head Stud Size: .493" Valve Guide OD: .502" Valve Job Type: Newen CNC 5 Angle Air Flow & Performance Criteria Intake Max. Flow: 370 CFM @ 0.700" Exhaust Max. Flow: 243 CFM @ 0.700" Intake Average Flow: 243 CFM Exhaust Average Flow: 170 CFM Intake Seat Material: Ductile Iron Intake Port Volume: 255cc Exhaust Port Volume: 106cc Standard Chamber Volume: 70cc Port Type: CNC Materials Cylinder Head Material: A356-T6 Aluminum Intake Valve Seat Material: Ductile Iron Exhaust Valve Seat Material: Ductile Iron Deck thickness: .750" Rocker Stand Type: Mast Billet Rocker Arm Type: LS3 1.7 or Aftermarket Guide Material: Phosphor Bronze General Rocker Stand Type: Mast Billet Rocker Stands Included: Yes Rocker Stand Dowels Included: Yes Uses Stock Rocker Bolts: No Rocker Bolts Included: No Rocker Arm Type: LS3 1.7 or Aftermarket Head Bolt QTY: 6 Bolt Style Valve Cover Rail Height: + ½ inch Can use OE Valve Cover: Yes Custom Options Available Chamber Softening Custom Chamber Sizing ½ inch head stud clearance Copper Exhaust & Intake Valve Seats