The LR4 is a 4.8L iron block truck engine that was introduced in 1999.

Along with the LM7 and LQ4, they were the first LS truck engines. The LR4 was available in GM pickups, vans, and SUVs until 2007. The 4.8L engine is also known as the Vortec 4800.

The engine specs and information here is for a stock LR4 engine.

These engines are strong and durable. Many people use them with boost or nitrous. With upgraded internals, the blocks can handle over 1,000 hp.

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 LR4 engine? Check out LR4 4.8L Engine Upgrade Guide: Expert Advice for LR4 Mods to Maximize Performance.]

The aftermarket is strong for LS swap engines. 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 LR4 4.8L iron block engine. 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.)

GM LR4 4.8L Engine Specs

Special Notes

  • The 1999-2000 LR4 with a manual transmission had a crankshaft with a 1.250 in. long rear flange. (Casting #12553312)
  • All other LR4 engines had a crankshaft with a 0.857 in. rear flange. (Casting #12553482)
  • In 2001, the LR4 and LM7 were upgraded with MLS gaskets.
  • The 1999-2003 LR4 and LM7 had a  return-style fuel injection system.
  • They went returnless in 2004 (except in the Express).

The information listed below is for the stock engine.

LR4 Performance Specifications

LR4 Engine Ratings
Compression Ratio9.4:1
Horsepower Rating255-280 hp
Torque Rating285-295 ft.-lbs.

LR4 Applications

LR4 Applications
VIN 8th DigitYearMakeModel
V1999-2006ChevroletSilverado 1500
V1999-2006GMCSierra 1500

LR4 Engine Block Specs

LR4 Block Specs
Casting Number12567392, 12567393, 12551358
Displacement4.8L / 293 c.i.d.
Bore Dia. 3.780 in.
Stroke3.267 in.
Deck Height9.2309.240 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. (1999-2003) Bore 1/5 = 2.326, Bore 2/4 = 2.317, Bore 3 = 2.307
Cam Housing Bore Dia. (2004-2006) Bore 1/5 = 2.346, Bore 2/4 = 2.326, Bore 3 = 2.307
Cam-to-Crank Centerline4.914 in.

LR4 Rotating Assembly

LR4 Rotating Assembly Specs
Piston MaterialHypereutectic Cast Aluminum Alloy
Piston StyleFlat Top
Piston Volume0cc
Wrist Pin Dia. (1999-2004)0.9447 in., 0.9448 in. (Pressed)
Wrist Pin Dia. (2005-2006)0.9429 in., 0.9431 in. (Floating)
Connecting Rod MaterialPowdered Metal
Connecting Rod StyleI-Beam
Connecting Rod Length6.275 in.
Connecting Rod BoltsM9 x 1 x 43
Crankshaft MaterialCast Iron
Crankshaft Main Journal Dia.2.559 in.
Crankshaft Rod Journal Dia.2.100 in.
Reluctor Wheel24x
Flywheel Mounting Flange (1999-2000)1.250 in.
Flexplate Mounting Flange (1999-2000)0.857 in.
Flexplate Mounting Flange (2001-2006)0.857 in.

LR4 Cylinder Heads

LR4 Cylinder Head Specs
Casting Numbers862,706
Combustion Chamber Volume61cc
Intake Port ShapeCathedral
Intake Runner Volume200cc
Exhaust Port ShapeOval
Exhaust Runner Volume70cc
Intake Valve Diameter1.890 in.
Exhaust Valve Diameter1.550 in.
Cylinder Head Bolt StyleTorque to Yield (TTY)
Cylinder Head Bolt Size (1999-2003) (8) M11 x 2 x 155, (2) M11 x 2 x 100, (5) M8 x 1.25 x 455
Cylinder Head Bolt Size (2004-2006)(10) M11 x 2 x 100, (5) M8 x 1.25 x 45

LR4 Camshaft Specs

LR4 Cam Specs
Duration @ .050 in. (int./exh.)191°/190°
Valve Lift (int./exh.)0.457 in./0.466 in.
Lobe Separation Angle (1999)115.5°
Lobe Separation Angle (2000-06)114°
Cam Gear Attachment3-Bolt

LR4 Valvetrain

LR4 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.1.890 in.
Exhaust Valve MaterialSteel, Solid Stem
Exhaust Valve Dia.1.550 in.

LR4 Throttle Body, Fuel Injector Specs & More

More LR4 Engine Specs
Intake ManifoldTruck-Style
Throttle Body78mm, 3-bolt
Throttle Control (1999-2002) All Cable Operated
Throttle Control (2003-2004)Drive-by-Wire phased in on most models
Fuel Injector Flow1999 - 21.8 lb/hr., 2000 - 24.8 lb/hr., 2001-2006 - 25.2 lb/hr.
Fuel Injector Length Between O-Rings 1.900 in.
Fuel Injector Connector Mini-Delphi / Multec2
Crankshaft Reluctor Ring24x
Camshaft Sensor LocationRear mount, 1x on Cam
Oil Pan
Deep Rear Sump
Oil PumpStandard Volume

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.