Ultimate Chevrolet Corvette C5 Z06 Mods Guide

When Chevrolet introduced the C5 Z06 Corvette in 2001, they powered it with their brand new 5.7 liter LS6 V8 engine. In 2001, the engine put out 385 horsepower and 385 lb-ft of torque, which bumped up to 405 horsepower and 400 lb-ft of torque from 2002–2004. At the time, these were pretty substantial power figures, but compared with the 670 horsepower the current C8 Corvette puts out, they could definitely use some inflation (the good kind). That’s why today we’re looking at the top Chevrolet Corvette C5 Z06 mods. Read on to find out how to make the most horsepower and torque from your LS6 powered C5 Z06 and CTS-V.

LS6 Engine Info and Vehicles

General Motors/Chevrolet produced the LS6 engine from 2001–2005. From 2001–2004, the LS6 appeared inside the brand new C5 Z06 Corvette, and from 2004–2005 it powered the also new Cadillac CTS-V. Both the Z06 and CTS-V were high performance variants of the base Corvette and CTS models. 

The LS6 is a 5.7 liter V8 engine that is part of GM’s third generation of small-block V8s. From the factory, it is naturally aspirated, and produces 385–405 horsepower and 385–400 lb-ft of torque. It is the high performance variant of the 5.7 liter LS1 engine, which Chevy introduced in 1999 in the base Corvette. The LS6 uses an aluminum engine block and cylinder heads, and the heads are cathedral-port style. It is an old-school overhead valve (OHV) pushrod V8, with a single in-block camshaft. 

In 2002, just one year after releasing the engine, the Chevy engineers made significant improvements that boosted both horsepower and torque. Enhancements for 2002+ included a hotter camshaft, strengthened valve train, freer flowing intake, and less-restrictive exhaust. These changes brought increases of 20 horsepower and 15 lb-ft of torque. 

Modded LS6 Engine Power Limits

Before looking at the top CTS-V and C5 Z06 mods, let’s look at the power limits of the LS6 engine. For most people, as long as you stay naturally aspirated and below 500 horsepower, the internals are usually very robust for most builds. When you start adding forced induction, through superchargers or turbochargers, the internals start to become more suspect. Additionally, the newest LS6 is still nearly two-decades old, so most of these engines have had some serious mileage under their belt, and aren’t exactly in “new” condition. 

Internally, the LS6 uses hypereutectic cast aluminum alloy M142, flat topped pistons. Starting midway through 2001, GM engineers changed the pistons to slightly reduce the piston-to-bore clearance and added polymer anti-friction coating. This was due to complaints about cold start piston slap amongst some customers. From 2004–2005, the pistons used full floating wrist pins, whereas from 2001–2003  they were press fit. The connecting rods are I-Beam-style and made from powdered metal, and the LS6 crankshaft is cast iron. 

Most people will say the engine block is good until around 800 horsepower, while the pistons and connecting rods are limited to ~500 horsepower (and 7,000 rpm). Upgrading to forged internals will allow for more horsepower and rpm, and should be done on builds surpassing 500 horsepower. 

Top 6 Chevrolet Corvette C5 Z06 Mods

Our top 6 Chevrolet Corvette C5 Z06 mods are:

• Colder Thermostat
• Cold Air Intake
• Long-tube Headers
• Upgraded Intake Manifold
• Upgraded Camshaft
• ECU Tuning

1) Corvette C5 Z06 Thermostat Upgrade

For our first of the C5 Z06 mods, we’re looking at upgraded performance thermostats. While this might not be the most familiar mod for some of our younger readers, for many years it has been a quick way to improve performance on the LS6 V8. It is a very cheap mod to do and relatively easy to install, and can really help those in extremely hot climates, like Arizona and Texas. The purpose of a thermostat in a car’s engine is to regulate the engine’s operating temperature. They are designed to keep an engine operating within a specified temperature range. 

Here’s how thermostats work. While the engine is still cold, the thermostat stays closed and keeps the coolant circulating within the engine block. After the engine reaches the minimum specified temperature, the thermostat opens and allows the coolant to flow into the radiator. The radiator’s job is to reduce the temperature of the coolant, so it can re-enter the engine to cool it and keep it operating within its optimal range. The thermostat constantly alters the flow of coolant in and out of the engine to regulate the temperature. 

Best Thermostat Upgrades

The reason for upgrading to a performance thermostat is that they operate in a lower temperature range than OEM. For the most part, OEM thermostats keep engine oil hotter because it improves fuel economy and reduces emissions. However, the trade-off is that it can hurt performance. This happens by forcing an engine to operate in a higher temperature range than is optimal for peak horsepower and torque. OEMs have to play a constant balancing game, as they have to make sure the engine runs hot enough that it doesn’t not overly pollute, while still producing good performance. 

That’s why upgrading to a colder performance thermostat will allow the engine to make better power. It will not increase the factory power output, but rather will allow the engine to perform better under the stock calibrations. When the engine gets too hot, the engine can reduce ignition timing and richen the air-to-fuel ratios. Running a colder thermostat helps prevent this from happening, allowing the engine to perform better after repeated runs. 

Importantly, the LS6 uses two different thermostats: One from the 2001–2004 (early models), and a different part for the (late model) 2004–2005 models. For 2001–2004 LS6 owners, here is a 160° thermostat from Lingenfelter Performance. For 2004–2005 LS6 owners (including all CTS-V owners), here is a 160° thermostat from EvenFlo. 

2) Chevy LS6 Cold Air Intake Upgrades

For our next bolt-on C5 Z06 mods, we suggest an upgraded performance intake. Sometimes called cold air intakes, they work a little differently on the C5 Corvette than other vehicles. Due to the unique construction of the Corvette engine bay, the intake filter pretty much has to stay in one position at the very front. This means that rerouting the filter for a true cold air intake is almost impossible on the C5 Z06. 

However, you can upgrade the air filter and factory tubing to gain an increase in air flow and velocity. By themselves, an upgraded C5 Z06 intake won’t gain tons of power. But when coupled with our other mods like long-tube headers, an intake manifold upgrade, and potentially forced induction, they will help unlock more performance. 

On the Cadillac CTS-V, a performance intake is a much better mod. Due to the more traditional layout of the engine bay, a cold air intake can be a solid upgrade due to the upgrading of the filter and tubing. 

Top Cold Air Intakes

Previously, we looked at upgrade intakes with our LS6 intake guide, so we’ll just summarize the top choices here. Make sure to check out the article for the full breakdown. Starting with the Cadillac, the top CTS-V cold air intake is the Lingenfelter CTS-V air induction kit. The Lingenfelter kit uses a large S&B filter and shows gains of 10 horsepower and torque on the dyno. 

For the Corvette intakes, the best option is the C5 Z06 SLP Blackwing intake. SLP is known for their collaborations with Pontiac on the Trans Am and Camaro, and their Corvette intake is also solid. It outflows the factory intake by 90% and can produce as much as 18 horsepower.

Another solid option is the C5 Vararam intake. The Vararam intake actually includes two additional intake scoops that help to draw in air from the lower in the bumper than the factory unit. This helps with lower intake temperatures without reducing airflow. Vararam claims as much as 40 horsepower gains throughout the power band, though it’s probably closer to around half of that. 

3) Corvette C5 Z06 Long-tube Header Mods

After upgrading the intake, another of the very popular C5 Z06 mods is to add long-tube headers. Long-tube headers replace the stock exhaust manifold, and they help to reduce back pressure and increase exhaust flow out of the engine. They also make the engine sound much louder and more aggressive. 

Compared with OEM, long-tube headers have wider diameter piping and a less restrictive design that is optimized for performance. This reduces the back pressure between the headers and the engine, which allows for much faster exhaust flow. Faster exhaust flow means more horsepower and torque. On the CTS-V, long-tubes will produce up to 25 horsepower and torque. On the C5 Z06, long-tube headers will produce closer to 15 horsepower and torque due to the less-restrictive factory exhaust. 

Importantly, when upgrading to long-tube headers on the C5 Z06 or CTS-V, you have to be aware of emissions laws. There are both catted and catless versions of long-tube headers, and high-flow catted ones are what you will most likely want. Catless headers are for track and race use only, meaning they are not street legal. However, high-flow cats offer very similar performance, and smell much better, and are the only legal options. 

Best Long-tube Headers

For the C5 Z06 Corvette and ‘04–’05 CTS-V, there are a ton of long-tube header options on the market. Starting again with the Cadillac, the CTS-V Kooks long-tube headers and green catalytic converter kit are very promising. They are more on the expensive side, largely due to the catalytic converters, but they offer solid performance and horsepower gains. Kooks makes their headers with 304 stainless steel, and the diameter is 1.875 inches.

For the Corvette, we also recommend C5 Z06 Kooks long-tube headers. These are similar to the CTS-V headers, but feature high-flow instead of “green” cats. The high-flow cats will allow for a little better performance, but they are not CARB certified. The final option is the American Racing Headers C5 Z06 long-tubes. These headers are available catless, and perform as well as the Kooks when used with high-flow cats. 

4) Corvette C5 Z06 Intake Manifold Upgrades

For our final intake mod, we’re looking at upgrading the intake manifold. Previously, we have looked at the top LS6 Intake manifold upgrades, so we’ll just summarize that here. Make sure to check out the article for the full, in-depth breakdown. The LS6 intake manifold is already one of the better ones from the factory. In fact, it was good enough that Chevy decided to retrofit it to the earlier LS1 engine starting in 2001. 

The intake manifold is the last step in the intake chain before the air reaches the engine. On the front is the throttle body which takes in air from the intake, and the manifold sits directly on top of the cylinder heads. Aftermarket intake manifolds offer superior flow characteristics than the stock manifold, and they are ideal if you are planning on running forced induction.

Best Intake Manifolds

Even though the stock LS6 manifold is decent from the factory, aftermarket manifolds have been proven to make significantly more power. Part of this has to do with pulse-reversion, which aftermarket intakes prioritize (checkout our above article for a breakdown of pulse-reversion).

The most popular C5 Z06 intake manifold is the FAST LSXR 102 mm manifold. It has been shown to pick up more than 30 horsepower 20 lb-ft of torque on the dyno and flows exceptionally. It looks very similar to the stock unit, but with new badging to make it look sleek. Of all the manifolds on the market, the FAST LSXR produces the most combined horsepower and torque throughout the power band. 

The other option is the Holley Hi-Ram EFI intake manifold. On the dyno, the Holley Hi-Ram has shown to make the most horsepower but less torque than the FAST intake. It flows exceptionally well, is very reasonably priced, and looks surprisingly nice. Some Corvette owners may have trouble with hood clearance, but it should fit without any modification. 

5) Corvette C5 Z06 Camshaft Upgrades

Next up on the list is C5 Z06 camshaft upgrades. Previously, we looked at the top LS6 camshaft upgrades, so we’ll just summarize the most important parts here. Make sure to check out the article for the full breakdown.

The camshaft is part of the valve train, and the LS6 uses an overhead valve train (OHV) with a single in-block camshaft. The LS6 inside the C5 Z06 used two different profile camshafts during its production run. For 2001, the LS6 used a cam that had an intake/exhaust duration of 204°/211°, with lift of 0.525”/0.525”, and a 116° LSA. From 2002-2005, the LS6 used a cam with an intake/exhaust duration of 204°/218°, with lift of 0.555”/0.551”, and a 117.5 LSA.

As you can see, the second LS6 cam was much hotter due to having more exhaust duration, greater lift, and a slightly wider LSA. The new hotter cam was partially responsible for the 20 horsepower and 15 lb-ft of torque increase in performance from 2001–2002 in the Z06. If you have a 2001 C5 Z06 a camshaft upgrade is a must, and on the 2002–2005 C5 Z06s they can still provide plenty of bang for your buck. 

Best C5 Z06 Camshaft Upgrades

Depending on the camshaft duration, lift, and LSA, you can add anywhere from 25-125 horsepower. However, the more horsepower they make, the worse they idle. Very high-lift and long-duration cams are really only recommended for track or drag racing use, as they will have poor drivability at lower loads when not being pushed hard. A middle-duration camshaft will provide decent horsepower and torque gains while maintaining idle quality and drivability. 

We have three recommendations on C5 Z06 camshaft upgrades, all of them from Livernois Motorsports. Livernois Motorsports offers a Stage 2 LS6 Camshaft, Stage 2R LS6 Camshaft, and a Stage 3 LS6 Camshaft. The most powerful is stage 3, while the least aggressive is stage 2. For most street builds, we suggest either the Stage 2 or Stage 2R camshafts. They will provide a good balance of performance and drivability. 

6) Corvette C5 Z06 ECU Tuning

Our final recommendation for C5 Z06 mods is ECU tuning. There are multiple types of ECU tuning, and we recommend custom flash tuning. Flash tuning involves taking a handheld tuning device, plugging it into the OBDII port beneath your dashboard, and installing aftermarket calibrations. These calibrations optimize parameters like air-to-fuel ratios, ignition and camshaft timing, and fuel pressure, to provide the most horsepower and torque. 

The factory tune on the Z06 is actually already pretty good from Chevy, but it still prioritizes fuel economy and emissions over performance in many cases. An aftermarket tune will really allow the LS6 to operate at its full potential, without the restrictive factory tuning. If you have other mods, like the bolt-ons we listed above, tuning will allow for your engine to take the most advantage of the increase in airflow and air volume. 

Top C5 Z06 Tuners

There are two main options when getting your C5 Z06 tuned: canned or custom tuning. Canned tuning (also known as off-the-shelf)  is a one-size-fits-all tune that is meant to apply to a specific engine and list of generic mods. They are not custom tailored to your specific vehicle with your brand-specific mods, but usually do an okay job at gaining horsepower. 

Custom tuning is the better option, as it allows a tuning professional to take an individualized look at your car with your brand-specific mods. The tuner can optimize the calibration for your specific mod-list and atmospheric conditions. Compared with canned tuning, a custom tune will provide more power within a safer margin of error. They are however much more expensive than canned tuning.

We generally recommend finding a local dyno tuner who has a good reputation with similar engines and cars for a custom tune. Most of the time, a single tune will run upwards of $500+, but it is well worth it. For those who do not have a local dyno tuner they feel comfortable with, there is also online or e-tuning. This process involves correspondence through email. It involves the tuning professional sending your individual files that you install on your car yourself. The tuner will have you log some driving, then they will make tweaks to the calibration based on how your car responds, much like on a dyno. 

The top e-tuner for the C5 Z06 is East Coast Supercharging (ECS). ECS have been supercharging and tuning Corvettes for many years, and the C5 community regards them very highly. You don’t need a supercharger setup for them to tune you, and their tunes are known for being powerful.  

Top C5 Z06 Mods FAQ