The Gen. 4, 6.2L, aluminum engines are light and durable, with many options for increasing power. On a stock engine, the following upgrades can improve performance and fuel economy:
Below are more upgrades that will improve the performance of the LS3 and L99 engines.
Engine Block
These engines share a 4.065 in. bore diameter. The cylinders can be bored to 4.080 in. However, we recommended leaving them as thick as possible when running boost. When bored and stroked, displacement can be as high as 427 c.i.d. (7.0 L).
The block can handle 850 to 1000 horsepower. However, you will want to upgrade to Head Studs and Main Studs if you plan on using boost or nitrous.
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. When stroking, choose a piston with minimal skirt taper. This prevents the piston from rocking at BDC and scraping up the skirts.
Gen. 4 rods are stronger than the Gen. 3's 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 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.
|
Gen. 4 Standard Spec. |
Stroke |
Rod Length / Wristpin |
Bore Size / Compression Distance |
|
L99 and LS3 (6.2L) |
3.622 in. |
6.098 in. / 0.9431 in. |
4.065 in. / 1.338 in. |
|
Common Stroker Combinations |
Stroke |
Rod Length / Wristpin |
Bore Size / Compression Distance |
|
6.2L to 6.8L |
4.000 in. |
6.125 in. / 0.927 in. |
4.070 in. / 1.110 in. |
|
6.2L to 7.0L |
4.100 in. |
6.125 in. / 0.927 in. |
4.070 in. / 1.050 in. |
|
6.2L to 7.0L |
4.125 in. |
6.125 in. / 0.927 in. |
4.070 in. / 1.050 in. |
Cylinder Heads
The L99 and LS3 heads have rectangle intake ports. The lighter hollow stem valves used in the LS3 can be installed in L99 heads to increase the rpm range. It is also common to CNC port and/or mill them up to 0.030 in. to increase compression and better airflow.
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. Be careful on an LS3. Piston-to-valve clearance is very tight with cams over 230° duration @ 0.050 in.
The L99 was equipped with Variable Valve Timing (VVT). When tuned correctly, it increases power over the entire rpm range. However, when used with a bigger cam, VVT can crash the valves. Some manufacturers offer Phaser Limiters and specially ground cams to ensure safe operation. Another option is to eliminate the VVT entirely with a VVT Delete Kit.
The L99 was also equipped with Active Fuel Management (AFM). It's good for gas mileage, but not high 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.
Switching from a 1-bolt to a 3-bolt cam is a popular option, when removing AFM and/or VVT components. Just make sure you get the timing set with the correct number of poles for your cam sensor. Most people use the 2006 Corvette 4X Gear. You will also want to replace the spring-loaded timing chain tensioner with an LS2-style Timing Chain Dampener.
Spring Kits are available for typical 0.600 in. lift cam upgrades. Titanium retainers are another upgrade that will reduce Valve Float.
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 and stud mounts is recommended for cams over 0.600 in. lift.
Intake Manifold and Throttle Body
The rectangle port intakes flow well, but an aftermarket intake can still make more power. Shorter runner intake manifolds and single plane intakes make more top end power, but can lose just as much low-end torque. Make sure the intended power band matches your gear ratio and torque converter.
At 90mm, the factory 4-bolt throttle body is fairly large and won't be a restriction in most applications. Most aftermarket intakes are designed to accommodate larger 102mm Throttle Bodies.
Power Adders
Many Supercharger Kits are bolt-on and work with stock internals and pump gas. More serious kits are available, but will require internal upgrades.
Nitrous Kits are also available, inexpensive, and easy to install. Street kits have lower settings that work with stock internals. More power requires higher settings and upgrading the engine internals.
Fuel System and Tuning
Upgrading to larger Fuel Injectors is often needed to meet the demand of increased power. The factory fuel pump will become a limitation around 575 hp. So, plan on upgrading the Fuel Pump as well.
Tuning the computer 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.