Upgrading the L92, L9H, and L94 Engines

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

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

The Gen. 4, 6.2L truck engines are closely related to the LS3 used in Corvettes and Camaros. Basically stock engines can make 650 hp. under boost. With upgraded internals, they can handle over 1,000 hp.

Below are some upgrades that will improve the performance of the L92, L9H, and L94 engines.

Engine Block

The engines share a 4.065 in. bore diameter and are commonly honed to 4.070 in. Boring to 4.080 in. is possible, but not recommended with boost. When bored and stroked, the 416 c.i.d. (6.8L) combination is common and 427 c.i.d. (7.0L) is possible. Aftermarket main studs are typically added when a forged rotating assembly is installed. Around 1000 hp., blocks are usually upgraded with billet main caps and cylinder sleeves.

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. The factory pistons also limit piston to valve clearance with larger cams. A set of Forged Pistons should be high on your priority list. A small domed piston can increase compression to around 11:1.

Gen. 4 rods are stronger than Gen. 3 and have full floating pins. They can handle about 850 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 1000 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. When you upgrade, a crankshaft with a longer stroke costs about the same and increases displacement.

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

Cylinder Heads

The cylinder heads are similar to the LS3 heads and make good power. Milling up to 0.030 in. can increase compression to 10.9:1. CNC porting is another popular option for more airflow. For high rpm engines (7,000+), LS3 intake valves are lighter and drop right in.

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 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.

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.

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.

VVT makes it hard to check piston to valve clearance when a bigger cam is installed. Some smaller aftermarket street cams require the use of a Phaser Limiter. A VVT Delete Kit is required if the phaser is having problems controlling a bigger cam with a lot of spring pressure.

Intake Manifold and Throttle Body

Factory intake manifolds are good and porting is a popular option. The shorter LS3 and other Aftermarket Intakes are used in most engine swap applications. 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 generally accept a 102 - 103mm Throttle Body.

Fuel System and Tuning

Upgrading to larger Fuel Injectors is often needed to meet the demand of increased power. The Flex Fuel injectors on the L9H and L94 flow 45% more than the L92 injectors and support over 600 horsepower on gasoline. The factory fuel pump will become a limitation around 550 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.