The HK, HT and HG Holden series produced between 1968 and 1971 were available with a range of durable and straightforward engines that helped establish Holden’s reputation for reliability and ease of servicing. These engines included Holden’s established inline six cylinder designs along with locally developed Holden V8 engines and Chevrolet small block V8 units. The following specifications summarise the key design features and dimensions of the engines used during the HK-HG production era and provide a useful reference for owners and restorers working on these classic Holden vehicles.
Holden Inline Six Cylinder and V8 Engines
Holden’s inline six cylinder engines were part of the well-known “red motor” family and were widely respected for their durability and smooth operation. These engines used a cast iron block and cylinder head with an overhead valve pushrod layout and hydraulic lifters.
Important design features included:
• Cast iron cylinder block and cylinder head
• Seven main bearing crankshaft
• Hydraulic valve lifters
• Pushrod operated overhead valves
• Full pressure lubrication system
161 Cubic Inch Six Cylinder
• Displacement: 161 cu in (2.64 L)
• Bore: 3.375 in (85.73 mm)
• Stroke: 3.00 in (76.20 mm)
• Compression ratio: approximately mid-8:1 range
• Power output: approximately 108–114 hp depending on specification
186 Cubic Inch Six Cylinder
• Displacement: 186 cu in (3.05 L)
• Bore: 3.625 in (92.08 mm)
• Stroke: 3.00 in (76.20 mm)
• Compression ratio: approximately 9:1
• Power output: approximately 126 hp
186S High Performance Six Cylinder
• Displacement: 186 cu in (3.05 L)
• Bore: 3.625 in (92.08 mm)
• Stroke: 3.00 in (76.20 mm)
• Improved carburetion and camshaft specification
• Power output: approximately 145 hp
Chevrolet 307 V8 Engine
The Chevrolet 307 small block V8 formed part of the engine range during the HK series and was derived from Chevrolet’s long-running small block engine family.
Key specifications include:
• Displacement: 307 cu in (5.03 L)
• Bore: 3.875 in (98.43 mm)
• Stroke: 3.25 in (82.55 mm)
• Compression ratio: 8.75:1
• Power output: 210 hp @ 4600 rpm
• Torque: 300 lb-ft @ 2400 rpm
• Firing order: 1-8-4-3-6-5-7-2
Holden 253 V8 Engine
The Holden 253 was the smaller version of Holden’s locally developed V8 engine family.
Key specifications include:
• Displacement: 253 cu in (4.2 L)
• Bore: 3.625 in (92.08 mm)
• Stroke: 3.062 in (77.77 mm)
• Compression ratio: approximately 8:1
• Cast iron block and cylinder heads
• Hydraulic lifters and pushrod valve train
Holden 308 V8 Engine
The 308 cubic inch engine became Holden’s flagship V8 powerplant and remained in production for many years.
Important specifications include:
• Displacement: 308 cu in (5.0 L)
• Bore: 4.000 in (101.60 mm)
• Stroke: 3.062 in (77.77 mm)
• Compression ratio: approximately 9:1
• Hydraulic lifter pushrod valve train
• Cast iron block and cylinder heads
Chevrolet 350 V8
Later HT and HG performance applications were associated with the Chevrolet 350 cubic inch small block V8, part of the same engine family as the 307.
Key specifications include:
• Displacement: 350 cu in (5.7 L)
• Bore: 4.000 in (101.60 mm)
• Stroke: 3.480 in (88.39 mm)
• Pushrod operated overhead valve layout
• Cast iron block and heads
Engine Construction and Lubrication
Despite differences in size and origin, the engines used during the HK-HG era shared similar design principles focused on strength and serviceability.
Important construction features include:
• Cast iron cylinder blocks and heads
• Aluminium alloy pistons with compression and oil control rings
• Precision removable crankshaft bearings
• Hydraulic valve lifters for automatic valve clearance
• Gear type oil pump supplying full pressure lubrication
Typical operating oil pressure specifications include:
• Approximately 30–45 psi during normal operation
• Warning indication if pressure drops to low levels
Correct specifications such as piston clearances, bearing tolerances, valve settings and lubrication pressures are critical when rebuilding or servicing these engines.
Holden HK HT HG Workshop Manuals
While this overview summarises the key specifications of the engines used during the HK-HG period, the Holden workshop manuals available from Car Manuals Direct include the original specifications, adjustment settings and repair procedures used by Holden mechanics when these vehicles were new.