LS6 5.7L Engine Upgrade Guide: Expert Advice for LS6 Mods to Maximize Performance

[Editor’s Note: This LS6 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. The LS6 is a Gen III, 5.7L aluminum-block V8 that first appeared in the 2001 Chevrolet Corvette Z06. It is dimensionally identical to the LS1 but does feature noteworthy differences to consider if you’re building an LS6 or planning to swap one into your vehicle.

For a primer on the LS engine universe, read LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family.]

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Intro to LS6 Engine Upgrades

The LS6 was the top performer of the Gen. 3 LS engine family and led directly to the Gen. 4 LS2 in 2005. It first appeared in the 2001 Corvette Z06 and was available in the C5Z until 2004. It also powered the Cadillac CTS-V in 2004 and 2005. It was light at 458 lbs. dressed with accessories. The LS6 became a legend in road-racing circles with the perfect balance of power and reliability.

The LS1’s 345 horsepower was quite an accomplishment which makes another sixty horsepower just five years later even more impressive. Some of the changes were:

• The LS6 intake manifold flowed more air and had a unique positive crankcase ventilation (PCV) system. It is the best factory Cathedral port car intake and was a popular swap onto LS1 engines.
• The LS6’s “243” casting cylinder heads flowed another 30 cfm. The airflow combined with hollow-stem intake valve and LS6 specific valve springs resulted in a redline that was 500 rpm higher than the LS1. In addition, the chambers were smaller for a healthy bump in compression ratio.
• LS6 cams have more duration and more lift. The cam used in 2002-05 had over .550 lift
• The bottom end was stronger as well. The LS6 engine blocks were sand cast and have windows in the bulkheads for better high-rpm breathing. The pistons also had a unique alloy and the rod bolts were stronger too.

Basic Bolt-Ons

On a stock LS6 engine, a few basic bolt-ons and tuning take the engine from 340 horsepower at the wheels to 400 hp.

• A cold air intake kit pays big dividends on the Corvette and CTS-V.
• Headers make power by themselves, but really start showing gains with other modifications.
• An aftermarket exhaust isn’t as critical on a Corvette, but helps the CTS-V quite a bit.
• A colder thermostat allows for more aggressive ignition timing.

These upgrades can be installed by anyone with simple hand tools. Once this is done, we recommend taking your car to the local chassis dyno tuner for a new baseline. This ensures everything is working as it should. It also makes it easier to gauge the gains from serious upgrades later.

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[Every engine spec you’ll need can be found here: LS6 Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More.]

Upgrading the LS6 Engine Camshaft and Valvetrain

LS6’s respond extremely well to cam swaps.

Lift as high as .600 in. on the street is common with valve spring kits. Titanium retainers are a plus along with .080 wall aftermarket pushrods. The engines have a lot of miles on them now so a trunnion kit is a good idea. Upgrading to LS7 lifters is another good move to increase RPM. LS timing chains don’t often break, but a single row C5-R chain is a good move as it fits under the timing cover without any grinding. The LS2 damper is another good upgrade to reduce chain-whip.

Upgrading the LS6 Engine Intake Manifold and Throttle Body

As good as the LS6 intake is, it was saddled with a 78mm throttle body with a three-bolt mounting flange. Aftermarket intakes use the bigger 4-bolt throttle bodies. The F.A.S.T. 102 is a popular intake and makes excellent power between 4,500 and 7,000 rpm. With good heads, it can pull past 7,000 rpm with ease. A 90mm LS2 (silver-blade) throttle body works with the factory ECU with minor tuning. 102mm throttle bodies are popular as well, but not critical. Relocating the IAT and going Speed-Density is another thing your tuner can do to remove the MAF restriction.

If hood clearance isn’t an issue, tunnel rams produce big gains at 6,000+ rpm. Single-plane intakes don’t make as much torque or power as the tunnel rams. But, for engines turning 5,500+ rpm (minimum) or using nitrous, they begin to make more sense.

Either way, now is a good time to install a 4-corner steam kit to reduce hot spots that cause #7 piston ring gaps to butt.

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

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Upgrading the LS6 Engine Fuel System and Tuning

 No matter how the power is achieved, the fuel system starts to become a limitation around 430 whp.

• Fuel injectors: The standard 30-lb. injectors support about 430 whp. Upgrading to larger injectors is needed for more. Keep in mind, the latest LS3-style injectors are the shortest, LS2 injectors were in the middle, and the LS1/6 injectors are the longest. This is a good time to involve your tuner as they will want a fully characterized injector to ensure peak driveability and power.
• Fuel pumps: The factory C5 Z06 pump is good for around 575 whp. There are multiple ways to bolster this with good voltage, bigger pumps, and electric voltage controllers.

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Upgrading LS6 Engine Cylinder Heads

The LS6 heads were good but there’s plenty of room for improvement.

• Porting: CNC ported heads can pick up another 50 cfm (totaling over 320 cfm @ .600 in. lift).
• Milling/Decking: The heads can be taken down to 60cc. This will build 11:1 compression which runs fine on pump gas. Be aware that piston-to-valve clearance will be reduced, but cams around 230° @ .050 in. can still work without flycutting.

• Lightweight LS3 intake valves can be cut to fit the seats. At 77 grams, they allow the engine to pull well beyond 7,000 rpm. The factory exhaust valves are already sodium filled and are often reused.
• With a good intake and a medium sized cam, 450-475 whp is common. These numbers are right up there with the mighty LS7.

You can save some downtime and increase performance further with a set of aftermarket heads. Often selling the original heads offsets the added cost. Heads in the 215-225cc range and up to a 2.040 in. intake valve will fit the 3.898 in. factory bore size. Additional deck thickness helps head gasket sealing with power adders.

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Adding a Supercharger or Nitrous Oxide System to the LS6

Many supercharger kits are bolt-on and work with stock internals and pump gas. A water-methanol injection kit is recommended. Over 600 horsepower at the wheels is just a start.

Nitrous kits and the LS6 go together like peanut butter and jelly. They’re widely available, inexpensive, and easy to install. Up to 200 horsepower is common on stock internals, but a proper tune and good fuel quality are part of the equation.

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Upgrading the LS6 Rotating Assembly

The stock pistons are a known weak point. As horsepower increases, so does heat—which, in turn, causes the top piston ring to expand. With enough heat, it will close the ring gap and the ends will butt together. When they do, a broken piston ring land is the result.

Broken ring lands can happen with as little as 450 hp in road racing or 600 hp in drag racing applications.

Another weak point of the stock pistons is that they don’t have valve reliefs, which limits piston-to-valve clearance. All of this is remedied by a set of forged pistons. Keep in mind, the LS6 shouldn’t be honed farther than 3.905 in.

The LS6 had stronger connecting rods and bolts than the pre-2001 LS1. With the exception of the late 2004 and 2005 CTS-V, they still had press-fit pins. These rods are good to 500 hp and 7,000 rpm (naturally aspirated). With boost or nitrous, 700+ hp can be achieved if rpm is limited to 6,500. At the same time, if you’re doing forged pistons, forged connecting rods are a popular upgrade.

Going with a 4 in. forged stroker crank will net 383 c.id. The added cubes compliment a heads/cam/intake top end by using the air up by 7,000 rpm. This matches the intake runner length tuning and hydraulic roller cam. Hitting 500 whp naturally aspirated is common for 383 strokers.

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Upgrading the LS6 Engine Block

If you’re running a power adder, the LS6 block is good for about 800 horsepower. At that point, the main caps start to walk as they are not doweled. Head and main studs help, but there are better options. A sleeved or aftermarket block and a 4.125 in. bore and 4 in. stroker crank nets 427 c.i.d. Iron blocks, sleeved aluminum 5.3L Gen. 4 blocks, and aftermarket 6 head bolt blocks are all common options. The LS6 block itself isn’t a good candidate for re-sleeving due to the windows cut into the main bulkheads.

(Information for this article originally appeared in this Upgrading the Gen. 4, 6.0L LS 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.)