The LS4 engine is a Gen. 4, 5.3L, aluminum small block engine used in GM cars between 2005 and 2009. It is unique because it was the only LS engine used in front-wheel drive vehicles.

The FWD LS4 had cathedral port cylinder heads and used Active Fuel Management (AFM). The engine was not Flex Fuel (E85) capable and did not use Variable Valve Timing (VVT) technology.

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 LS4 engine? Check out LS4 5.3L FWD Engine Upgrade Guide: Expert Advice for LS4 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 guide is specifically about the GM LS4. You can find our other LS engine spec guides and LS-related tech articles here.

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

Chevy LS4 Engine Specs

LS4 Basic Stats

RPO Code
VVTAFMFlex Fuel (E85)Cylinder Head
Intake Port Shape

To make this engine work, GM made several modifications to the engine:

  • The engine was mounted in a transverse position, using unique motor mounts.
  • The intake manifold was smaller than other LS manifolds and reversed, placing the throttle body over the flexplate.
  • The engine used a metric, 60-degree, Chevrolet V6 bellhousing.
  • The starter was mounted on the transmission, not the engine block.
  • The timing cover, crankshaft, and accessory drive were all modified to fit in the FWD engine bays.

Because of its unique configuration, the LS4 is usually NOT a good candidate for an engine swap.

The information listed here is for a stock engine.

LS4 Performance Specifications

LS4 Engine Ratings
Compression Ratio10:1
Horsepower Rating303 hp
Torque Rating323 ft.-lbs.

LS4 Applications

LS4 Applications
VIN 8th DigitYearMakeModel
C2005-08PontiacGrand Prix GXP
C2006-07ChevroletMonte Carlo SS
C2006-09ChevroletImpala SS
C2008-09BuickLaCrosse Super

LS4 Engine Block Specs

LS4 Block Specs
Casting Number12569004
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 in. Bore 2/4 = 2.326 in. Bore 3 = 2.307 in.
Cam-to-Crank Centerline4.914 in.

LS4 Rotating Assembly

LS4 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
Rod Part Number
Rod Casting

(Last 3 Digits)
Crankshaft MaterialCast Iron
Crankshaft Part Number12568920
Crankshaft Casting Number
(Last 3 Digits)
Crankshaft Main Journal Dia.2.559 in.
Crankshaft Rod Journal Dia.2.100 in.
Crankshaft Length13mm Shorter than Standard (-10mm snout, -3mm rear flange)
Reluctor Wheel
(2005-Early 2007)
Reluctor Wheel
(Later 2007-09)

LS4 Cylinder Heads

LS4 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

LS4 Camshaft Specs

LS4 Camshaft Specs
Camshaft Part Number1256952512625436
Duration @ .050 in. (int./exh.)193°/193°196°/201°
Valve Lift (int./exh.)0.482 in./0.482 in.0.481 in./0.481 in.
Lobe Separation Angle114°116° +2
Cam Gear Attachment3-Bolt1-Bolt
Cam Gear Poles1x4x
Active Fuel Management (AFM)YesYes
Variable Valve Timing (VVT)NoNo

LS4 Valvetrain

LS4 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 Style
Timing Chain Guide Style
Spring Loaded Tensioner

Other Key LS4 Specs

LS4 Throttle Body, Fuel Injector Specs & More
Intake Manifold Part Number12604786
Intake ManifoldCar-Style (Reversed)
Intake Manifold Part Number
Intake Manifold Part Number
Throttle Body76mm, 4-Bolt, Gold Blade (Non-standard Bolt Pattern)
Throttle Control Electronic, Drive-by-Wire
Fuel Injector Part Number 12580681
Fuel Injector Flow30 lbs./hr. @ 58 psi
Fuel Injector Length Between O-Rings 1.73 in.
Fuel Injector Connector EV6 / USCAR
Crankshaft Reluctor Ring
(2005-Early 2007)
Crankshaft Reluctor Ring
Camshaft Sensor LocationTiming Cover
Oil Pan
Centered Sump
Oil PumpHigh Volume, 1.25 c.i./rev.

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.

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