The LR4 is a 4.8L iron block truck engine that was introduced in 1999.
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
- 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|
|Horsepower Rating||255-280 hp|
|Torque Rating||285-295 ft.-lbs.|
|VIN 8th Digit||Year||Make||Model|
LR4 Engine Block Specs
|LR4 Block Specs|
|Casting Number||12567392, 12567393, 12551358|
|Displacement||4.8L / 293 c.i.d.|
|Bore Dia.||3.780 in.|
|Deck Height||9.2309.240 in.|
|Bore Spacing||4.400 in.|
|Thrust Bearing Location||#3 Main|
|Main Cap Style||6-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 Centerline||4.914 in.|
LR4 Rotating Assembly
|LR4 Rotating Assembly Specs|
|Piston Material||Hypereutectic Cast Aluminum Alloy|
|Piston Style||Flat Top|
|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 Material||Powdered Metal|
|Connecting Rod Style||I-Beam|
|Connecting Rod Length||6.275 in.|
|Connecting Rod Bolts||M9 x 1 x 43|
|Crankshaft Material||Cast Iron|
|Crankshaft Main Journal Dia.||2.559 in.|
|Crankshaft Rod Journal Dia.||2.100 in.|
|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|
|Combustion Chamber Volume||61cc|
|Intake Port Shape||Cathedral|
|Intake Runner Volume||200cc|
|Exhaust Port Shape||Oval|
|Exhaust Runner Volume||70cc|
|Intake Valve Diameter||1.890 in.|
|Exhaust Valve Diameter||1.550 in.|
|Cylinder Head Bolt Style||Torque 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 Attachment||3-Bolt|
|LR4 Valvetrain Specs|
|Lifter Style||Hydraulic Roller|
|Lifter Link Style||Plastic Lifter Tray|
|Lifter Body Diameter||0.842 in.|
|Pushrod Length||7.385 in.|
|Rocker Arm Mounting Style||Pedestal|
|Rocker Arm Style||Die-Cast, Roller Fulcrum|
|Valve Spring Style||Beehive|
|Valve Spring Color||Natural|
|Valve Angle||15 Degrees|
|Intake Valve Material||Steel, Solid Stem
|Intake Valve Dia.||1.890 in.|
|Exhaust Valve Material||Steel, Solid Stem|
|Exhaust Valve Dia.||1.550 in.|
LR4 Throttle Body, Fuel Injector Specs & More
|More LR4 Engine Specs|
|Throttle Body||78mm, 3-bolt|
|Throttle Control (1999-2002)||All Cable Operated|
|Throttle Control (2003-2004)||Drive-by-Wire phased in on most models|
|Fuel Injector Flow||1999 - 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 Ring||24x|
|Camshaft Sensor Location||Rear mount, 1x on Cam|
|Oil Pan||Deep Rear Sump|
|Oil Pump||Standard 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.