The LH6 engine is a 5.3L Gen. IV aluminum engine that replaced the LM4 in 2005. It was the first Gen. IV LS truck engine and offered Active Fuel Management (AFM).

The LH6 was available in mid-size SUVs until 2009, and in GM pickups from 2007-09. For marketing purposes, it was also known as the Vortec 5300. The engine specs and information listed here is for a stock LH6 engine.

Mechanically similar, General Motors’ LS and LS-based Vortec engines wound up on almost every branch of the GM family tree: Chevy, Pontiac, GMC, Cadillac, Buick—heck, even Saab, Hummer, and Isuzu got some LS love.

Since LS and Vortec engines are so common, they’ve become the go-to performance and swap engines of the modern era.

These motors are capable of making a lot of horsepower, and respond well to upgrades like turbos, superchargers, high-flow cylinder heads, intake systems, cams, and nitrous oxide.

[Looking to upgrade your LH6 engine? Check out LH6 5.3L Engine Upgrade Guide: Expert Advice for LH6 Mods to Maximize Performance.]

The aftermarket is strong, crate engines are available, and used motors are often cheaply sourced through junkyards.

Summit Racing has created a series of comprehensive guides for each engine in the LS family, so engine builders and tuners can have a handy reference for their projects.

This specific guide is for the GM LH6 5.3L Vortec 5300.

You can find more LS engine spec guides and LS-related information here.

(Summit Racing’s Paul Spurlock and Brian Nutter contributed to this article.)

LH6 5.3L Vortec 5300 Engine Specs

LH6 Performance Specifications

Engine Ratings
Compression Ratio9.9:1
Horsepower Rating302-315 hp
Torque Rating330-338 ft./lbs.

LH6 Applications

VIN 8th DigitYearMakeModel
M2005-06ChevroletTrailblazer EXT
M2005-06GMCEnvoy XL, XUV
M2005-09GMCEnvoy Denali
M2005-09Saab9-7X 5.3i, ARC
M2007-09ChevroletSilverado 1500
M2007-09GMCSierra 1500

LH6 Engine Blocks

LH6 Engine Block Specs
Casting Numbers125771048, 12601900, 12569513, 12568573
Displacement5.3L / 325 c.i.d.
Bore Dia. 3.780 in.
Stroke3.622 in.
Deck Height9.240 in.
Bore Spacing4.400 in.
Thrust Bearing Location#3 Main
Main Cap Style6-Bolt
Main Housing Bore Dia.2.751 in.
Cam Housing Bore Dia.Bore 1/5 = 2.346, Bore 2/4 = 2.326, Bore 3 = 2.307
Cam-to-Crank Centerline4.914 in.

LH6 Rotating Assembly

LH6 Rotating Assembly Specs
Piston MaterialHypereutectic Cast Aluminum Alloy
Piston StyleFlat Top
Piston Volume0cc
Wrist Pin Dia.0.9431 in. (full floating)
Connecting Rod MaterialPowdered Metal
Connecting Rod StyleI-Beam
Connecting Rod Length6.098 in.
Connecting Rod Housing Bore2.225 in.
Connecting Rod BoltsM9 x 1 x 43
Connecting Rod Part Number12649190
Connecting Rod Casting Number (last 3 digits)143
Crankshaft MaterialCast Iron
Crankshaft Part Number12574522
Crankshaft Casting Number (last 3 digits)216
Crankshaft Main Journal2.559 in.
Crankshaft Rod Journal2.100 in.
Reluctor Wheel24X (2005-06), 58X (2007-09)

LH6 Cylinder Heads

LH6 Cylinder Head Specs
Casting Numbers799, 243
Combustion Chamber Volume65cc
Intake Port ShapeCathedral
Intake Runner Volume210cc
Exhaust Port ShapeD-Port
Exhaust Runner Volume75cc
Intake Valve Diameter2.000 in.
Exhaust Valve Diameter1.575 in.
Cylinder Head Bolt StyleTorque to Yield (TTY)
Cylinder Head Bolt Size(10) M11 x 2 x 100, (5) M8 x 1.25 x 45

LH6 Camshaft Specifications

LH6 Camshaft Specifications
Part Number1256952512625436
Duration @ .050 in. (int./exh.)Not Available196°/201°
Valve Lift (int./exh.)Not Available0.481 in./0.481 in.
Lobe SeparationNot Available116°+2
Cam Gear Attachment3-Bolt1-Bolt
Cam Gear Poles1x4x
Active Fuel Management (AFM) YesYes
Variable Valve Timing (VVT)NoNo

LH6 Valvetrain

LH6 Valvetrain Specs
Lifter StyleHydraulic Roller
Lifter Link StylePlastic Lifter Tray
Lifter Body Diameter0.842 in.
Pushrod Length7.385 in.
Rocker Arm Mounting StylePedestal
Rocker Arm StyleDie-Cast, Roller Fulcrum
Rocker Ratio1.7
Rocker OffsetNone
Valve Spring StyleBeehive
Valve Spring ColorNatural
Valve Angle15 Degrees
Intake Valve MaterialSteel - Solid Stem
Intake Valve Dia.2.000 in.
Exhaust Valve MaterialSteel - Solid Stem
Exhaust Valve Dia.1.575 in.
Timing Chain Guide StylePlastic Guide (2005-06), Spring Loaded Tensioner (2007-09)

NOTE: You can find engine specs and detailed engine upgrade advice for every LS and LS-based Vortec truck engine in one place: The Definitive Guide to LS Engine Specs and LS Engine Upgrades.