Engine Guides / LS Engines

LS3 Engine Upgrade Guide: Expert Advice for LS3 Mods to Maximize Performance

[Editor’s Note: This LS3 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 LS3 engine is a Gen IV, 6.2L aluminum-block V8 car engine that first appeared in the 2008 Chevrolet Corvette. The L99—introduced for the 2010 Chevy Camaro SS—is also a Gen IV 6.2L aluminum-block V8, but with the addition of Active Fuel Management and Variable Valve Timing. Below you’ll see references to the L99 as a result. For a primer on the LS engine universe, read LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family.]

Intro to LS3 Upgrades

On a stock LS3 engine, the following upgrades can improve performance and fuel economy:

[Every engine spec you’ll need for an LS3 project can be found here: LS3 Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More.]

The LS3 and L99 are both Gen IV, 6.2L, aluminum block, car engines which came under the hoods of GM performance cars between 2008 and 2017. Both the LS3 and L99 engine blocks can be pushed to 850 to 1,000 horsepower.

Both engines use rectangle port cylinder heads and have a common 4.065-inch bore diameter. They also have the internal oil passages for Active Fuel Management (AFM), even if unused.

It is common for owners of GM performance vehicles with AFM-equipped LS or LS-based Vortec engines to delete or disable the cylinder-deactivation feature to maximize engine power.

For more on that, read: How to Delete or Disable Active Fuel Management (AFM) on GM Engines.

How to Tell the Difference Between LS3 and L99

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 much closer. The major differences between these engines is the special technology used in the cylinder heads which you can learn more about here.

If you have an LS3 and are on the hunt for the best mods, you’re in the right place. Here’s the roadmap to upgrading your LS3 powerplant to achieve maximum performance.

(Summit Racing’s Paul Spurlock contributed to this article.)

Upgrading the LS3 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.

[Trying to find an LS engine for a swap or build? Check out Part 1 and Part 2 of our LS Spotter’s Guide.]

Upgrading the LS3 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-degree duration @ 0.050 inch.

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.

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 pounds) can pull the bolts out of the cylinder head. Converting to roller rockers and stud mounts is recommended for cams over 0.600-inch lift.

Upgrading the LS3 Fuel System and Tuning the Engine

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 limited. Custom tuning requires more knowledge, but will provide even better performance.

Adding an LS3 Supercharger or Nitrous Oxide System

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.

Upgrading LS3 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 inch to increase compression and better airflow.

There are many aftermarket cylinder 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.

4-corner steam kit is another smart upgrade. It reduces hot spots in cylinder #7 that can cause the piston rings to butt and crack the piston.

Upgrading the LS3 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.

Standard vs. Performance Specs for LS3 Rotating Assemblies

Gen IV LS Standard SpecStrokeRod Length / WristpinBore Size / Compression Distance
LS33.622 in.6.098 in. / 0.9431 in.4.065 in. / 1.338 in.
Common Stroker CombinationsStrokeRod Length / WristpinBore Size / Compression Distance
6.2L to 6.8L4.000 in.6.125 in. / 0.927 in.4.070 in. / 1.110 in.
6.2L to 7.0L4.100 in.6.125 in. / 0.927 in.4.070 in. / 1.050 in.
6.2L to 7.0L4.125 in.6.125 in. / 0.927 in.4.070 in. / 1.050 in.

Upgrading the LS3 Engine Block

LS3 engines (as well as the L99) have a 4.065-inch bore diameter.

The cylinders can be bored to 4.080 inch. 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.

(Information for this article originally appeared in this Upgrading the Gen. 4, 6.2L, 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.

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  1. Can you swap out an LS1 engine with an LS3 engine bell housing motor supports ect?

    • Hey Carroll.

      Replacing the LS1 with an LS3 is a popular conversion. The LS1 engine mounts, bellhousing pattern, and exhaust ports are the same. The LS1 water pump and accessory drive can be used.

      Although you could use the Chevrolet Performance NAL-19354328 LS controller kit, it only runs the engine. It requires LS3 sensors and it doesn’t connect to the factory dash or control an automatic transmission. To keep the rest of the car functioning, it’s easiest to retain most of the LS1 electronics, then have the car tuned for the power increase.

      Here’s what to do:

      Block Mods:
      LS1 knock sensors should be re-used for the correct signal. Opening up the LS3’s side-mounted knock sensor pads is done with an 8.5mm drill bit and tapping with an M10 x 1.5 tap. The Casper’s Electronics extender harness CEI-109081 is used. The LS3’s block mounted dipstick hole is plugged because the LS1 pan already has the provision. The original oil pan, pickup, windage tray, O-ring NAL-12557752 and pump can be swapped between the LS1 and LS3.

      Electrical Mods:
      The LS3’s cam sensor is on the timing cover instead of the rear of the block. This is achieved with the same CEI-109081 adapter harness noted in the knock sensor extension. The LS3 has a 58x reluctor vs. 24x…. That is most easily solved with a Lingenfelter 58x -> 24x converter box LPE-L460065397.

      Intake Mods:
      MAP sensors moves from back to front and can be extended with Casper’s CEI-109080. The LS1 MAP sensor is a loose fit in the LS3 manifold, but it can be sealed with an extra O-ring and Rtv in a pinch. A true LS3 MAP sensor could be used with the CEI-109103 adapter.

      If you have an old 1997-00 3-wire MAF, adapt to the less restrictive 2001+ type 5-wire with integrated IAT sensor. To do this requires Casper’s CEI-108100, a couple inches of 3-inch silicone hose, and re-tuning the MAF table in the ECU.

      Fuel rail adapters are required if the car has a return-style fuel system. The LS3 injectors are better than the old LS1’s in spray pattern and accuracy. The tuner will have LS3 injector characterization information. Casper’s EV1 harness to EV6 injector USCAR plug adapters p/n CEI-109077 will be required. The LS3 injectors are shorter and fit the LS3 fuel rail without spacers or extra O-rings.

      Throttle Body:
      Both the LS1 and LS6 are 3-bolt throttle bodies which don’t bolt to the 4-bolt LS3 intake. The LS1 Corvette is Drive-by-wire and can use a 2005-08 90mm LS2 or LS3 Silver blade TB with Casper’s adapter harness CEI-108115 (along with re-scaling). The LS1 F-Body and 2004 GTO are cable throttles and 4-Bolt 90mm+ throttle bodies are widely available.

  2. Pingback: LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family - OnAllCylinders

  3. Pingback: Ask Away! with Jeff Smith: Explaining 6-, 8-, and 10-Speed Automatic Transmission Gearing - OnAllCylinders

  4. David Guiraud says:

    Would you suggest a fuel pump upgrade or boost for a TSP stage 3 cam staying n/a? What about injectors?

    • I am running an MTI racing stage 2 cam which is 227/239 .614/.624 on stock injectors and pump. on a mustang dyno I have 484rwhp and 449tq. your stage 3 should be close to that or better depending on supporting mods that you have.


    Yes trying to find out how much horsepower I have on my Corvette it has a 6.8l supercharged engine has been dyno tested up to 720 hp thks

  6. I can’t believe I read that entire discussion.

  7. Can you use a 24x 4.00 crankshaft in the LS3 block, with 6.125 con rods and the stock 4.065 pistons?

  8. Clarke Brown says:

    Looking at putting a ls3 in a sprint car running on methonal not aloud electronic fuel induction looking at holly meth carb not sure what manifold to use will upgrade cam and springs might do heads see how money goes any idea on mechanical fuel pump

    • Does it have to be mechanical fuel pump per rules? Return style with electric pump and pressure regulator will work fine if your allowed. If not, they sell belt driven mechanical fuel pumps that will work on ls3.

  9. Pingback: LS3 Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More

  10. Is there anyway to get rid of the drive by wire for the LS3? trying to do a ls3 in my 240 and I want a ls3 but i really dislike the drive by wire style tbody.

    • Hey Evan, short answer is yes. but it’s not as easy as just slapping on a new throttle body and running a cable to the pedal.

      Because changing from a drive-by-wire to cable-driven throttle body is actually a very big deal. Gen. 4 computers work with 58X reluctors, but don’t have the chip required to run hte IAC valve in a cable throttle body. Most 1999 to 2003 ECMs and some automotive ’04s will run the IAC but don’t work with 58X.

      If you want a cable throttle body and 58X, a stand-alone engine management system like a Holley Terminator is the least expensive option.

  11. Jim Chamberlain says:

    What spark plug should I use for my Gen 4 LS3 with headers?

  12. Bruce Bryant says:

    Have a LS-3 427 625hp in my 1976 Corvette, coupled to a 5 speed Tremick transmission. Has 850 Holley & high rise manifold. I am experiencing two problems.
    This car is used on street.

    1. Plug fouling. How hot can I go safely on plug @ sea level. Flordia

    2. Bucks badly in 5th gear without being on the throttle .

    • What are your cam specs? A CAM with a ton of overlap with a 850 carb could foul out plugs during idle. A lot of overlap with a carb is a nightmare at idle and lower rpm in my experiance. Turn your idle up to 900-1000rpm and see if you still foul out plugs.

  13. If your running a stand alone management system i dont see why you couldnt go from 58 to 24. Wont be able to run 24 on stock ecm from a gen4 ls3

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