(Image/LS1Tech – SgtSkid)
The LM4 is a 5.3L, Gen. 3 small block engine used in GM trucks between 2003 and 2005.
It’s is very similar to the LM7, except that it’s built on an aluminum block, and the LM7 is an iron-block engine.
For marketing purposes, the LM4—like the LM7—was also known as the Vortec 5300. The engine specs and information listed here is for the stock LM4 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.
[NOTE: Looking to upgrade your LM4? Read: LM4 5.3L Engine Upgrade Guide: Expert Advice for LM4 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 LM4 truck 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.)
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GM LM4 Engine Specs
| LM4 Engine Ratings | |
|---|---|
| Compression Ratio | 9.5:1 |
| Horsepower Rating | 290-300 hp |
| Torque Rating | 325-335 ft.-lbs. |
| LM4 Applications | |||
|---|---|---|---|
| VIN 8th Digit | Year | Make | Model |
| P | 2003-2005 | Chevrolet | Trailblazer EXT |
| P | 2003-2004 | Chevrolet | SSR |
| P | 2003-2004 | GMC | Envoy XL |
| P | 2004 | Buick | Rainer |
| P | 2003-2004 | Isuzu | Ascender |
| LM4 Block Specs | |
|---|---|
| Casting Numbers | 12566910 |
| Material | Aluminum |
| Displacement | 5.3L / 325 c.i.d. |
| Bore Dia. | 3.780 in. |
| Stroke | 3.622 in. |
| Deck Height | 9.240 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. (2003) | Bore 1/5 = 2.326, Bore 2/4 = 2.317, Bore 3 = 2.307 |
| Cam Housing Bore Dia. (2004-05) | Bore 1/5 = 2.346, Bore 2/4 = 2.326, Bore 3 = 2.307 |
| Cam-to-Crank Centerline | 4.914 in. |
| LM4 Rotating Assembly Specs | |
|---|---|
| Piston Material | Hypereutectic Cast Aluminum Alloy |
| Piston Style | Dished |
| Piston Volume | +8cc |
| Wrist Pin Dia. (2003-04) | 0.9447 in., 0.9448 in. (Pressed) |
| Wrist Pin Dia. (2005) | 0.9429 in., 0.9431 in (Floating) |
| Connecting Rod Material | Powdered Metal |
| Connecting Rod Style | I-Beam |
| Connecting Rod Length | 6.098 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. |
| Reluctor Wheel | 24X |
| LM4 Cylinder Head Specs | |
|---|---|
| Casting Numbers | 862, 706 |
| Material | Aluminum |
| 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 (2003) | (8) M11 x 2 x 155, (2) M11 x 2 x 100, (5) M8 x 1.25 x 45 |
| Cylinder Head Bolt Size (2004-05) | (10) M11 x 2 x 100, (5) M8 x 1.25 x 45 |
| LM4 Camshaft Specs | |
|---|---|
| Duration @ .050 in. (int./exh.) | 191°/190° |
| Valve Lift (int./exh.) | 0.457 in./0.466 in. |
| Lobe Separation Angle | 114° |
| Cam Gear Attachment | 3-Bolt |
| LM4 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 |
| Rocker Ratio | 1.7 |
| Rocker Offset | None |
| 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. |
| LM4 Throttle Body, Fuel Injector Specs & More | |
|---|---|
| Intake Manifold | Truck Style |
| Throttle Body | 78mm, 3-Bolt |
| Throttle Control | Drive-by-Wire |
| Fuel Injector Flow | 25.2 lbs./hr. @ 58 psi |
| Fuel Injector Length Between O-Rings | 1.9 in. |
| Fuel Injector Connector | Mini-Delphi / Multec2 |
| Fuel Rail (2003) | Return-Style |
| Fuel Rail (2004-05) | Returnless |
| PCM | Warren |
| Crankshaft Reluctor Ring | 24x |
| Camshaft Sensor Location | Rear Mount, 1x on cam |
| Oil Pan | Front sump, tunnel in pan for 4WD, center filter |
| 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.
What is the price of the LM4 crate engine ?
Hey Mike, Chevrolet Performance used to offer an LM4 crate engine under part number 12491855, but it appears to have been discontinued. So your best bet may be sourcing one through a junkyard. We’ve got
a pair of Spotter’s Guides that may help.
There are companies that make a few 5.3L LS crate engines (LM7), and the price range varies on whether you need just a short block or a fully-dressed long block.
5,3 hiw much please long block
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Does the lm4 and l33 have the same block?