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Having a capacity of 5.3 liters (325 cu in), GM/Chevrolet LM4 is a naturally aspirated V8 90° 4-stroke gasoline motor. It’s a representative of Generation Three V8 truck motors with small blocks. LM4 resembles LM7 (released between 2003 and 2005), but it differs by having an aluminum block.
Chevrolet LM4 (Vortec 5300) keeps V8 90° aluminum cylinder block featuring 5-bearings crankshaft, 2 aluminum heads, one cast camshaft and 2 valves per cylinder (16 in total). The motor is supplied with a multiport fuel injection system plus an electronic throttle body of 78 millimetres. It utilizes a “Coil-Near-Plugs” ignition system, consisting of a complex distributor, spark plug wires with a low level of resistance and spark plugs with platinum tips.
The motor has a compression index of 9.5, 96 millimetres (3.78 inches) cylinder bore plus 92 millimetres (3.62 inches) piston stroke. The output ranges from 290 hp (294 PS or 216 kW) at 5200 rpm 300 hp (304 PS or 224 kW) at 5200 rpm. Torque is between 325 ft/lb (441 Nm or 45.0 kg/m) at 4000 rpm and 335 ft/lb (454 Nm or 46.3 kg/m) at 4000 rpm.
LM4 Engine Specs
|Engine code||GM / Chevy LM4 (Vortec 5300)|
|Layout||Four stroke, V8|
|Fuel type||Gasoline (petrol)|
|Displacement||5.3 L, (325 cu in)|
|Fuel system||Sequential multi-port fuel injection|
|Power output||294 PS (216 kW; 290 HP) at 5,200 rpm
304 PS (224 kW; 300 HP) at 5,200 rpm
|Torque output||441 N·m (45.0 kg·m, 325 ft·lb) at 4,000 rpm
454 N·m (46.3 kg·m, 335 ft·lb) at 4,000 rpm
|Dimensions (L x W x H):||–|
|Cylinder block alloy||Aluminum|
|Cylinder bore:||96.0 mm (3.78 in)|
|Piston stroke:||92.0 mm (3.62 in)|
|Number of piston rings (compression / oil):||2 / 1|
|Number of main bearings:||5|
|Cylinder inner diameter (standard):||96.000-96.018 mm (3.7795-3.7802 in)|
|Piston skirt diameter (standard):||96.000 mm (3.7795 in)|
|Piston pin outer diameter:||23.997-24.000 mm (0.9448-0.9449 in) (2003-2004)
23.950-23.957 mm (0.9429-0.9431 in) (2005)
|Piston ring side clearance:||Top||0.045-0.080 mm (0.0018-0.0031 in)|
|Second||0.040-0.078 mm (0.0016-0.0031 in)|
|Oil||0.012-0.200 mm (0.0005-0.0079 in)|
|Piston ring end gap:||Top||0.23-0.44 mm (0.0091-0.0173 in)|
|Second||0.44-0.70 mm (0.0173-0.0276 in)|
|Oil||0.18-0.75 mm (0.0071-0.0295 in)|
|Connecting rod small end diameter||24.000 mm (0.9449 in)|
|Connecting rod big end diameter:||56.505-56.525 mm (2.2246-2.2254 in)|
|Connecting rod center distance:||159.38 mm (6.275 in)|
|Crankshaft main journal diameter:||64.993-65.007 mm (2.5588-2.5593 in)|
|Crankpin diameter:||53.318-53.338 mm (2.0991-2.0999 in)|
The motor keeps an aluminum cylinder block featuring 5-bearings crankshaft supported system. The diameter of the crankshaft journal is 65 millimeters (2.55 inches) while the crankpin diameter equals to 53.3 millimeters (2.09 inches).
With the compression index of 9.5, LM4 features 96 millimeters (3.78 inches) cylinder bore plus 92 millimeters (3.62 inches) piston stroke. The motor is equipped with 2 compression plus 1 oil control rings. Connecting rods are 154.89 millimeters (6.098 inches) long.
|Block head alloy||Aluminium|
|Valve Arrangement:||OHV, chain drive|
|Cylinder head height:||120.2 mm (4.7323 in)|
|Valves:||16 (2 valves per cylinder)|
|Intake valve timing:||190°|
|Exhaust valve timing:||191°|
|Valve head diameter:||INTAKE||48.0 mm (1.8898 in)|
|EXHAUST||39.4 mm (1.5512 in)|
|Valve stem diameter:||INTAKE||7.955-7.976 mm (0.3132-0.314 in)|
|EXHAUST||7.955-7.976 mm (0.3132-0.314 in)|
|Valve spring free length:||INTAKE||52.9 mm (2.0827 in)|
|EXHAUST||52.9 mm (2.0827 in)|
|Camshaft lobe lift:||INTAKE||6.96 mm (0.274 in)|
|EXHAUST||6.82 mm (0.2685 in)|
|Camshaft journal diameter:||54.99-55.04 mm (2.165-2.1669 in)|
The great cooling potency is ensured by the sturdy but light aluminum alloy the cylinder heads are made of. The cylinder heads used are 862 or 706. The camshaft is run by a single chain. The timing chain conveys the rotational motion from the crankshaft to the camshafts. Pedestal mounting rocket arms control valves.
The intake valves are 48 millimeters (1.89 inches) while the exhaust ones are 39.4 millimeters (1.55 inches). The motor keeps intake duration of 190 degrees plus 11.60 millimeters (0.457 inches) intake valve lift. Simultaneously, the exhaust duration is 191 degrees and the exhaust valve lift equals to 11.84 millimeters (0.466 inches). The angle of the lobe separation is 144 degrees.
|Chevrolet TrailBlazer EXT||2003–2005|
|GMC Envoy XL||2003-2004|
LM4 Engine problems and reliability
How to Add Boost to LM4 Engine
While iron 5.3-liter block can cope with increased power, the motor supports more than 850 wheels horsepower .
If you want increase the engine performance, consider updating the injectors and fuel system.
Bear in mind that four-corner steam kit decreases hot sports, which make the rings strike the piston’s ring lands.
A nitrous oxide kit (at low settings) will be suitable for street driving with internal components. Up to a 200-shot is normal. Remember that the efficiency can be limited by a piston ring gap. Meanwhile, a single-plane intake can hardly be damaged by a nitrous backfire. While plate system keeps more efficient distribution than the initial intake, the first place is occupied by eight-nozzle fogger system. Moreover, it’s advisable to opt for the fuel with more octane.
The truck engine bays are ideal for installing turbochargers. You are able to increase the performance by turbo exhaust manifolds, which are rather affordable. If you opt for a single turbo, the T4 hot-side is suitable, but the exhaust flow will be restricted by small turbine diameters. Besides, note that the 650 wheels horsepower will start to feel like 400 in hurry. V-band style exhaust housings are compatible with bigger turbines and facilitate plumbing. Meanwhile, twin turbochargers cost more, but give you more space to grow.
A Roots-style supercharger is rather trustworthy and is ideal for melting tires. It leads to increased torque at low and medium rpm.
A centrifugal-style supercharger is rather lightweight. Thanks to a larger intercooler, located in the radiator front, it’s able to produce more power at high rpm.
How to Update the LM4 Engine Rotating Assembly
The compression index of Chevrolet LM4 dished pistons is 9.5.
It’s considered to be rather low for a naturally aspirated motor, but well-directed if you deal with boost addition.
When you start to increase the motor output, you may face problems with cast pistons and butting rings.
Thus, feel free to check the benefits of using forged pistons. They feature more durable wristpins, more massive rings lands and extra valve reliefs, which allow running large camshafts. If you aim to reach more than 800 wheel horsepower, it’s advisable to employ a kit of .200 in. wall tool-steel pins.
Within the first two years of production, this motor used Generation Three rods, but they are pretty risky. They are able to cope with 650+ wheel horsepower and 7000 rpm in boosted employment. Being influenced by real route conditions, the rods may bond and later break.
By having forged pistons, think about utilizing forged connecting rods as well. 7/16-inch rod bolts will help you to get rid of many troubles even if rpm is more than 7000.
The motor’s crank is cast, but very enduring. It can cope with more than 1000 wheel horsepower.
If you need to add cubic inches for increased boost, that’s the reason to use stroker forged crank. In such a way, you will reach better turbos performance.
Last update on 2021-10-16 / Affiliate links / Images from Amazon Product Advertising API