ATK HPLS1250 LS1/LS6 61cc/250cc Cylinder Heads Assembled (Each)

Description

Specifications:
Material A356 Aluminum
Bolt Count 6 Bolt Head
Intake Port Volume 250cc
Intake Port Dimension 3.227″H x 1.119″W
Intake Port Location Stock Cathedral Port
Intake Valve Size 2.080”
Intake Valve Material Stainless Steel
Exhaust Port Volume 105cc
Exhaust Port Dimension 1.628″H x 1.722″ W
Exhaust Port Location .086″ Raised
Exhaust Valve Size 1.60”
Exhaust Valve Material Stainless Steel
Combustion Chamber Size 61cc
Valve Cover Bolt Pattern Perimeter Bolt
Valve Angle 11° Degree
Valve Spring Pocket Diameter 1.610″ O.D
Valve Spring Pac 1905 Dual Spring (Hyd. Roller)
Valve Spring Setup Height 1.800”
Valve Spring Closed Pressure 160lbs (W/Retainer)
Valve Spring Open Pressure 1.200” .600” Lift 425lbs / 1.150” .650” Lift 445lbs (W/Retainer)
Valve Spring Max Lift .650”
Valve Guide Material Manganese Bronze
Valve Seal Material Viton
Valve Seat Material Powder Metal
Retainer Material Titanium
Deck Thickness .750″
Minimum Bore Diameter 3.900″ (will not fit stock bore 4.8L/5.3L)
Flat Mill .006” per cc
Spark Plug Dimensions 14mm x .708″ with Tapered Seat
Torque Specifications Per Application Based on Factory or Aftermarket Bolts/Studs

Recommended Components:
Intake Port Gasket Factory GM
Exhaust Port Gasket Factory GM
Head Gasket Factory Block 3.900” + GM#12589226 – 4.000” + GM#12610046 or Per Application
Head Gasket Aftermarket Block 4.125” + Cometic MLX Per Application
Head Bolts Get proper head bolts and length for your head and block combo.
Head Studs Get the proper head stud diameter and length for your head and block combo.
Spark Plug Starting Range NGK TR55
Lifters .600” + applications we suggest an aftermarket Tie Bar Lifter
Pushrods 3/8 Pushrods are recommended (must check length)
Rocker Arms Stock Rocker arms with upgraded Trunnions or Aftermarket

Disclaimer: It’s up to the installer to verify all fitment and components will work on the engine. Everything listed is just a recommendation. ATK is not responsible for damage to heads or engines due to miss matched components or wrong application.

These cylinder heads are Flow Tested on a Super Flow SF600 bench with a 4.030” bore size @28” water. Clay intake radius was used, Flow tube was not used on the exhaust port.

In.        Ex.
Lift 0.100”        65        58
Lift 0.200”       140      103
Lift 0.300”       214      145
Lift 0.400”       260     182
Lift 0.500”       302      217
Lift 0.600”       315       227
Lift 0.700”       303      234