[Editor’s Note: This L76 engine upgrade guide is the second in a series of LS engine upgrade guides assembled by a team of LS experts at Summit Racing. The L76 engine is a Gen IV, 6.0L aluminum-block V8 car engine that first appeared in the 2006 Holden VZ Commodore, but most in the USA will recognize it as the engine that powered the 2008-09 Pontiac G8 GT. There was also a truck version of the L76 introduced in the 2006 Silverado/Sierra that added VVT on top of AFM technology. In this article we’ll concentrate on the car engine. For a primer on the LS engine universe, read LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family.]
[Every engine spec you’ll need for an L76 project can be found here: L76 Car Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More.]
The L76 is a Gen IV, 6.0L, aluminum block, car engine which came under the hoods of GM performance sedans between 2006 and 2010. In some ways, it bridged the gap between the LS2 and the LS3. It used the same block as the LS2, but had rectangle port heads similar to the LS3. In this trim, it made 361 horsepower and 385 Ft./Lbs. of torque.
Without the VVT system used on the truck engine, it had true flat top pistons which resulted in a higher compression ratio of 10.4:1.
They are equipped with Active Fuel Management (AFM) which was activated in the U.S. models. It was left disconnected on the Holden’s with the exception of the 2009-10 Holden’s equipped with automatic transmissions.
How to Tell the Difference Between L76 and other engines
At first glance, these engines look very similar. The easiest way to tell them apart is to check the 8th digit of the VIN code.
If you don’t have the VIN, you will need to look closer. Unlike the LS2 or LS3, it will have the ribbed AFM valley cover.
The aluminum block is cast with 6.0 on the back right-hand side and it has a casting number 12568952. The cylinder heads will have either the 5364 or 823 casting numbers.
If you have an L76 and are on the hunt for the best mods, you’re in the right place. Here’s the roadmap to upgrading your L76 power plant to achieve maximum performance.
Intro to L76 Car Engine Upgrades
For many people, upgrading the L76 starts off with a cold air intake kit.
The factory exhaust system is restrictive in an effort to reduce the drone while in 4-cylinder mode. A set of headers and an aftermarket exhaust system will make more power, but the drone can become obnoxious. So how do we deal with that? Easy, we tune it out with an AFM disabler or increase overall performance with a programmer.
The factory tune was conservative.
We recommend that you talk with your local chassis dyno tuner to choose a computer programmer. Here are some of the benefits:
- Tune out AFM activation.
- Correct the fuel and ignition timing tables.
- Raising the factory redline will keep your vehicle in the meat of the powerband longer.
- Raise shift points and firmness.
- Shut off torque limiting.
Getting a tune makes it easier to dial in a bigger cam and injectors later. Before going to the tuner, we recommend installing a colder thermostat to open up the tuning window.
Below are other upgrades you can make to improve the performance of an L76 engine.
Upgrading the L76 Car Engine’s Camshaft and Valvetrain
As we mentioned earlier, the engine came with AFM—which is known to fail.
And if you’re in this deep, why not put a cam in it?!
For more on that, read: How to Delete or Disable Active Fuel Management (AFM) on GM Engines.
If you’re still driving daily, cams in the 215-220 degree intake-duration range can be tuned to idle nearly stock and still provide good mileage.
Cams in the 220-226 range are a little more serious, but are still easy to tune, and driveability is still good.
What are the limitations to going bigger?
Piston to valve clearance with a L76 is tight. There are specific cams in the 230-234 range with intake valve events specially designed to clear the piston without flycutting.
What if you already have a power adder?
Generally, supercharger cams and nitrous cams will have slightly more lobe separation and longer exhaust duration. Turbo cams reduce overlap with less exhaust duration split in relation to the intake.
|Intake Duration (@ 0.050 in.)||Horsepower at the wheels after bolt-ons||Idle Quality||Notes|
|196° (Stock)||305-315 whp||Smooth|
|215°||+60 hp||Slightly noticeable||Good with auto and stock converter.|
|220° - 230°||+80 hp||Steady lope||Converter recommended. Still can drive daily.|
|230° - 240°||+110 hp||Lopey||Fly-cutting the pistons may be required. Heads and intake good for another 40+ hp.|
The stock rockers are good up to 175 lbs. of seat pressure and 450 lbs. open. You will want to install a trunnion kit for added reliability.
Tech Tip: When you’re pulling the cam, switch out the spring-loaded timing chain tensioner for the more reliable wedge-style (early) LS2 damper.
Adding an L76 Supercharger or Nitrous Oxide System
L76 engines are a popular choice for people who want to keep their engine naturally aspirated, but if you do decide to boost, here are a couple of things to address:
- A 4-corner steam kit reduces hot spots that can cause the rings to butt and snap the piston’s ring lands.
- The 42 lb. fuel injectors will support around 525 whp which is where most power-adders are just getting started. We’ve addressed those in the next section on fuel system upgrades.
Okay, here’s the fun stuff:
- A nitrous kit (at low settings) is great for street driving with stock internals. Up to a 200-shot is common. Keep in mind the tight piston ring gap is the limiting factor beyond that. If you’re wanting to get serious, a single-plane intake is less prone to break from a nitrous backfire. A plate system has better distribution than the original intake, but an eight-nozzle fogger system is even better. Running higher octane fuel is advised.
- Turbo kits are everywhere. The least-expensive kits start with the factory exhaust manifolds feeding twins in the trans tunnel area. From there you will find tubular manifold kits with the turbo’s placed in the front upper corners of the engine bay. Horsepower increases start at 600 whp and goes up from there. Common street kits are capable of 1000+ whp with the right fueling and well-built engine.
- A Roots-style supercharger is dependable and makes great torque in the low- and mid-rpm range. It’s so good that GM used one on their own LSA-powered ZL1. Horsepower ranges from 520-700 whp with higher levels of boost.
- A centrifugal-style supercharger is lightweight and makes more power at high rpm. This is partially due to a larger intercooler mounted in front of the radiator. They don’t have quite the curb appeal of a Roots, but make great power.
Upgrading the L76 Fuel System and Tuning
The L76 came with 42-lb. injectors that can support roughly 525 whp. The most common upgrade is the LSA/LS9 injector. It bolts in and flows close to 30 percent more fuel. Fuel injector characterization info is widely available, but you’ll still want to talk to your tuner about it before the swap.
|Year||Part Number||Flow @ 58 PSI||Connector||Length (Inches between O-rings)||Approx. WHP Limit|
|2010-15||L99 12639221||42 lbs.||Uscar EV6||1.496 in.||525|
|2009-14||LSA/LS9 12598646||59 lbs.||Uscar EV6||1.496 in.||750|
The fuel pump becomes an issue around 520 whp. The first option is to maintain or increase pump pressure with electronic voltage controllers and hotwire kits. From there, the ZL1 pump will drop into the factory tank and supports roughly 650 whp. When running boost, you can use a water-methanol system to supply extra fuel and lower charge air temps.
Upgrading the L76 Intake Manifold and Throttle Body
GM really did its homework with the factory intake and throttle body. Below 6000 rpm, it’s unbeatable with the exception of the Edelbrock Cross-Ram. There are some applications where other intakes make sense.
A standard runner length FAST manifold makes a few more horsepower, but some of that comes from the addition of a larger throttle body. The mid-length runner version would be a good option for serious racecars operating at 6000+ rpm at all times. It’s worth about 15-20 hp at 7000 rpm, but loses as much torque below 5500 rpm. This limits its use to serious road race cars, or pure drag cars with 5500+ stall converters.
How about a single plane intake? There are two main reasons to do this. One is a carb swap, but that would be a rarity with the L76. What would be more common is the guy that really loves his nitrous. The square bore plate style systems have better distribution to the individual cylinders than the L99 intake. This and the added strength would make it a good fit for this application. It will make another 20 hp at 7000 rpm, but the crossover doesn’t occur until 6500 rpm and it will consistently be down 30 ft.-lbs. of torque from idle to 5500 rpm.
Not afraid of hood scoops and 7000+ rpm? The taller Tunnel Rams will lose up to 30 ft.-lbs. torque below 5000 rpm. Horsepower matches at 6000 rpm and the Tunnel Ram will add another 25 hp by 7000 rpm.
Whichever direction you go, be sure to ask your tuner about going with a speed density tune. Doing so will remove the MAF restriction and give you more power.
Upgrading L76 Cylinder Heads
The L76 cylinder heads are similar to the LS3 heads except they used a heavier solid stem intake valve.
- The stock heads can be CNC-ported for more airflow. Flow numbers can be as high as 373 cfm at .700 lift. Lightweight hollow-stem LS3 valves will drop right in. Between the light valves and better springs, the engines will pull cleanly to 7000 rpm. If you’re looking to boost to 800+ hp; a heavy-duty aftermarket stainless intake valve is a bit tougher and won’t tulip as quickly from the heat. Milling the heads .030 will bump compression to 10.9:1 and will increase power everywhere. Piston-to-valve clearance will be tight with cams beyond 230 at .050 in. of intake duration.
- A better option is aftermarket heads. They reduce downtime, they’re all-new, and you can usually offset the added cost by selling your original heads. Valve angles are typically laid over to 13.5 degrees for increased piston-to-valve clearance. They flow better and the cross-sections are great for naturally aspirated or boosted engines. When comparing heads, look at the .400 in. lift numbers as a general indicator of how the heads will perform. With a medium-sized cam, 500+ whp (naturally aspirated) is a goal that is easily met.
Upgrading the L76 Rotating Assembly
On the L76 engine, pistons are the weak link and you probably already know someone who has popped one.
A set of forged pistons is a good idea and you can increase compression while you’re at it.
They have stronger wristpins, thicker ring lands, and the added valve reliefs allow you to run big cams. If you’re going over 1000 hp, or use a 300+ shot of nitrous, a set of .200 wall tool-steel pins is a good idea.
The L76’s Gen. 4 rods are stronger than the Gen. 3 rods and have full floating pins. They can handle about 800 hp and 7000 rpm in boosted applications (at least for a while). They are likely to bend before they break when subjected to real track conditions.
If you’re getting forged pistons, upgrade to forged connecting rods at the same time. Big 7/16-inch rod bolts will go a long way to keep things together over 7000 rpm.
The L76 crank was cast but strong. The main reason for a stroker crank is added cubic inches. With heads and manifolds available that breathe well above 7000 rpm, more cubes can bring the power peak back into hydraulic roller territory for more power under the curve.
Performance rotating assemblies are available in many combinations.
A couple notes of caution when stroking the engine:
- The 6.0L aluminum blocks had slightly longer cylinder sleeves than the iron blocks (5.500 in. vs. 5.430 in. on average). When running a stroker crank, much of the piston skirt drops out of the bottom of the cylinder at BDC. The best piston manufacturers have compensated for this by eliminating skirt taper until a point well above where it meets the bottom of the cylinder sleeve at BDC. Any skirt taper at this intersection acts as a razor blade and will quickly wear out the piston. This is especially true with a 4.100 or longer stroke, and the piston design is critical to long life.
- The blueprint deck height of the block is 9.240 in. It’s best to measure deck height before ordering your rotating assembly. Thicker head gaskets or using an aftermarket 6.098-6.100 in. rod will ensure enough piston-to-head clearance.
|Engine Size||Bore Dia.||Piston Comp. Height||Stroke||Rod Length||Wristpin Dia.|
|L76 6.0L (364 c.i.d. - stock)||4.000 in.||1.338 in.||3.622 in.||6.098 in.||0.943 in.|
|6.0L to 6.7L (408 c.i.d.)||4.030 in.||1.110 in.||4.000 in.||6.125 in.||0.927 in.|
Upgrading the L76 Engine Block
L76 engines have a 4.000-inch bore diameter.
The cylinders can be bored to 4.030 inch. However, we recommended leaving them as thick as possible when running boost.
You can make 850 whp with a couple of simple upgrades like head studs and LS9 head gaskets. Race gas, E-85, or water-methanol injection is required.
The factory main caps aren’t doweled. It’s better to reduce ignition timing and compensate with added boost to reduce the cylinder pressure spikes that can lift heads and cause the main caps to dance.
Main studs should be added any time you’re this deep in the engine.
(Information for this article originally appeared in this Upgrading the Gen. 4, 6.0L, LS Car Engines article at Summit Racing’s searchable database of FAQ tech info. Go there and search “LS engines” for a comprehensive collection of LS engine tech information.)
NOTE: You can find engine specs and detailed engine upgrade advice for every LS and LS-based Vortec truck engine in one place: The Definitive Guide to LS Engine Specs and LS Engine Upgrades.