Upgrading the LH6, LC9, LH8, and LH9 Engines

On a stock engine, the following upgrades can improve performance and fuel economy:

• A Cold Air Intake Kit
• Headers
• An Aftermarket Exhaust
• A Computer Programmer

The aluminum block 5.3L engines are light weight. They also have thick cylinder walls, which are good for strength and durability. These engines were also available in a wide range of popular vehicles. This means they can be easier to find than some other engine models.

The Gen. 4, 5.3L, aluminum engines also had cathedral port heads, similar to the LS1, LS2, and LS6. There are tons of performance parts available, and most will bolt right on.

Below are some upgrades that will improve the performance of the LH6, LC9, LH8, and LH9 engines.

Engine Block

The engines share a 3.780 in. bore diameter. The thick cylinder walls are great for high boost applications. The cylinders can be safely bored to LS1 size for low boost applications. When bored and stroked, displacement can be as high as 383 c.i.d. (6.3L).

When stroking, choose a piston with 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. They will crack in high horsepower engines. A set of Forged Pistons should be high on your priority list.

Gen. 4 rods are stronger than Gen. 3 and have full floating pins. They can handle about 800 hp. and 6,500 rpm in boosted applications. If you’re getting forged pistons, upgrade to Forged Connecting Rods at the same time.

Even though it’s 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 Crank early in your build will save you the headache later. When you upgrade, a 4.000 in. stroke crankshaft costs about the same and increases displacement.

With domed pistons and mid-range cam, compression around 11:1 range is possible on pump gas.

The chart below lists standard specs compared to common performance Rotating Assemblies.

Cylinder Heads

The cathedral port cylinder heads are similar to the LS2 heads and make good power. Milling up to 0.030 in. and CNC porting adds more compression and airflow. For high rpm engines (7,000+), LS3 intake valves are lighter and can be cut to fit.

There are many Aftermarket Heads available. The heads flow better and have thicker decks to maintain head gasket seal. A wide range of runner and chamber volumes are available. Some also go from a 15 degree to a 13.5 degree valve angle for even more power.

A 4-Corner Steam Kit is another smart upgrade. It reduces hot spots in cylinder #7 that cause the piston rings to butt and crack the piston.

Camshaft and Valvetrain

LS engines respond well to Cam Swaps. In addition to valve springs and rockers, the cam needs to match the compression, torque converter, rear-end gears, etc.

Performance valvetrain parts from the LS1, LS2, and LS6 fit these heads. Spring Kits are available for typical 0.600 in. lift cam upgrades. Titanium retainers are another option to reduce

The trunnion bearings in the stock rocker arms are another known weak point. A Trunnion Upgrade Kit should be installed when you upgrade the valvetrain. Upgrading to Full Roller Rockers is another option.

The stock rockers are pedestal mounted. High spring pressure (over 475 lbs.) can pull the bolts out of the cylinder head. Converting to roller rockers is recommended for cams over 0.600 in. lift.

The LH6 and LC9 are equipped with Active Fuel Management (AFM). It's good for gas mileage, but not for performance. If the valvetrain is in good condition, an AFM Disabler can turn the AFM off. When upgrading to a performance cam, an AFM Delete Kit is strongly recommended. These kits replace all the AFM components with standard parts.

Piston-to-Valve clearance and high spring pressure (over 400 lbs.) can be a problem with Variable Valve Timing (VVT) used on the LH9 and LC9. Some aftermarket street cams require the use of a Phaser Limiter. A VVT Delete Kit is another option. Completely removing the VVT components is more common with larger street/strip and race cams.

Intake Manifold and Throttle Body

Factory intake manifolds are good and porting is a popular option. The shorter LS6 and other Aftermarket Intakes are often used for hood clearance in an engine swap. The engine bays in trucks (or cars with hood scoops) may accommodate a tunnel ram.

At 87mm, the factory 4-bolt throttle body is fairly large and isn’t a restriction in most applications. Aftermarket intakes are generally designed to accomodate larger Throttle Bodies.

Fuel System and Tuning

Upgrading to larger Fuel Injectors is often needed to meet the demand of increased power. The Flex Fuel injectors flow 25% more than standard and replace the stock injectors without any other modifications. The factory fuel pump will become a limitation around 400 hp. So, plan on upgrading the Fuel Pump as well.

Truck engines have a conservative tune from the factory. Tuning the ECM changes the fuel and ignition curves to increase performance. Plug-In Programmers are easy to use, but they do have limits. Custom tuning requires more knowledge, but will provide even better performance.