[Editor’s Note: This L99 engine upgrade guide is part of a series of LS engine upgrade guides assembled by a team of LS experts at Summit Racing that we are sharing at OnAllCylinders. For a primer on the entire LS engine universe, read LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family.]
Intro to L99 Engines
The L99 was introduced in 2010 and powered the Gen. 5 Camaros that were equipped with automatic transmissions. This engine was advanced with VVT and AFM, and made 400 horsepower and 410 foot-pounds of torque.
Why were there two different 6.2L engine options in the Camaro? At the time, AFM wasn’t operating smoothly enough with manual transmissions, so those cars got the LS3.
[Every L99 engine spec you’ll need can be found here: L99 6.2L Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More.]
How to Get More Power From Your L99 Engine (Bolt-Ons)
For many people, upgrading the L99 starts with adding a cold air intake.
The factory exhaust system is very restrictive in an effort to reduce the 4-cylinder mode drone. A set of headers and aftermarket exhaust system flow a lot of air, but the drone becomes 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 L99 engine.
Upgrading the L99 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?!
The first thing to decide is whether you want to maintain VVT.
What are the downsides to VVT?
More serious cams often require 400 lbs. of valve spring open pressure. This makes it hard for the phaser to actuate. In addition, tuning VVT is a little more complex. If you don’t want to deal with that, a VVT delete kit is an option. It opens the door to a wide selection of camshafts.
Generally, 3-bolt cams are more common and only requires the addition of a 3-bolt 4-pole upper gear to convert it.
If you’re still driving daily, cams in the 215-220 degree intake-duration range can be tuned to idle like 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 L99 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
|Good with auto and stock converter.
|220° - 230°
|Converter recommended. Still can drive daily.
|230° - 240°
|Fly-cutting the pistons may be required. Better cylinder heads are 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. Want to save some shop labor? You can buy rockers with the trunnion kits already installed. This also saves you the cost of the installation tool.
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.
L99 Power Adders
L99 engines are a popular choice for people that want to stay 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 L99 Fuel System and Tuning
The L99 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.
|Flow @ 58 PSI
|Length (Inches between O-rings)
|Approx. WHP Limit
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 L99 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 L99. 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 L99 Cylinder Heads
The L99 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 10.8:1 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 L99 Rotating Assembly
On the L99 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 L99’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 L99 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 6.2L 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 of the 427 c.i.d. combination, 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.
|Piston Comp. Height
|L99 6.2L 376 c.i.d. (Stock)
|6.2L to 6.8L
|6.2L to 7.0L
Upgrading the L99 Engine Block
The L99 engine block has a 4.065-in. bore diameter. It wasn’t torque-plate honed from the factory and the cylinders aren’t particularly strong. Usually the bores are torque-plate honed to 4.070 in. From there, custom pistons and rings are available in .005 in. increments.
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 anytime you’re this deep in the engine.
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.