On a stock engine, the following upgrades can improve performance and fuel economy:
The LR4, LM7, and L59 have very strong blocks. They can handle over 1,000 hp. using nitrous, a blower, or a turbo. However, you will need to upgrade the internals to handle that kind of power.
The biggest bonus of buying a 4.8L or 5.3L engine is the low cost. They are also easier to find than the higher displacement engines. LS1 and LS6 based performance parts are plentiful and many will bolt right on.
Below are some upgrades that improve the performance of the LR4, LM7 and L59 engines.
Engine Block
The 4.8L and 5.3L have small 3.780 in. bores. Although they can be bored to LS1 sizes (3.898 in.+), the extra thickness can help head gasket seal. When combined with a 4.000 in. stroke, displacement can be as high as 383 c.i.d. (or 6.3L).
The iron blocks have slightly shorter cylinder lengths than the aluminum blocks. When stroking, choose a piston with a minimal skirt taper. This prevents the piston from rocking at BDC and scraping up the skirts.
Rotating Assembly
The stock pistons are a known weak point of these engines. They have a history of cracking around the wrist pin and the top ring land. A set of Forged Pistons should be high on your priority list.
Boosted, the stock rods will handle about 700 hp. and 6,500 rpm. If you go higher, get Forged Connecting Rods.
Standard 6.098 in. length and pin is one option. 6.125 in. length and .927 in. pin is another. Forged piston companies have offerings for both. Keep in mind the original pressed fit and full floating pins had different diameters. Most forged pistons use the original larger pressed-pin diameter. The rod may require small-end honing to fit.
Even though it is cast, the crankshaft can handle about 900 hp. and 7,000 rpm (for a limited time). A broken crankshaft is bad news. Upgrading to a Forged Crankshaft early in your build will save you the headache later. If you upgrade, a 4 in. stroke crank costs no more and gives you added displacement.
Performance Rotating Assemblies are also available.
Cylinder Heads
Having the stock heads CNC machined will improve air flow and power. 4.8L and 5.3L engines have small intake valves. Going to a 2.000 in. intake valve adds flow. Lightweight LS3 valves can be cut to fit the seats as well.
There are also many Aftermarket Heads available. These heads have thicker decks to maintain headgasket seal. They have a range of intake and exhaust runner volumes. Various combustion chamber sizes are also available.
A 4-Corner Steam Kit can reduce hot spots that can cause #7 ring end gaps to butt.
Camshaft and Valvetrain
LS engines respond extremely well to
There are a number of great Spring Kits available that match the typical hydraulic roller upgrades. For those on a tight budget with stock cams, LS6 springs reduce valve float.
The trunnion bearings in the stock rocker arms are another known weak point. Retrofit Trunnion Kits are available if you reuse the stock arms. Upgrading to Full Roller Rockers is another popular upgrade, when lift approaches 0.600 in.
Stock rocker arms are pedestal mounted. High spring open pressures (475+) can pull the bolts out of the cylinder head. Converting to stud or shaft mounted rockers is recommended over 0.600 lift.
Intake Manifold and Throttle Body
The factory truck-style manifold makes more power and torque than car intakes, but are 3 in. taller. If you are swapping the engine into a car, an LS6 intake is a good budget intake. The 90mm+ aftermarket intakes make more top end horsepower than the truck manifold. Keep in mind an automotive front accessory drive will be required.
When changing intakes, take note of the Throttle Body. The stock manifold is 78mm and uses a 3-bolt mounting flange. Many aftermarket manifolds use a 90mm or larger throttle body and use a 4-bolt flange.
Depending on the year and model the engine came from, the throttle could be controlled differently. Some vehicles used a cable to control the throttle. Others used a drive-by-wire set up.
Fuel System and Tuning
Upgrading to larger Fuel Injectors is often needed to meet the fuel demand of increased power. Custom tuning will be required to properly adjust the fuel and ignition systems.