There is no shortage of LS builds scattered throughout the internet showing how far boost can push stock components. It seems like once a week, you see a new junkyard 5.3-liter LS build aiming to go past 1,000-horsepower using a stock block, rotating assembly, and cylinder heads. But, while the stock guts are surprisingly durable, our next LS engine build project is looking to make big power and be able to live for a long time. So after stumbling upon a great deal on a pair of new-old-stock LS9 cylinder heads in bare form, we snagged them quickly and gave a call to Ferrea for one of their valve and spring kits.

What Is An LS9?

The LS9 was at the heart of the C6 ZR1 Corvette. This special LS was exclusive to the C6 ZR1 and contained several special features that allowed its Eaton TVS2300 supercharged 6.2-liter V8 to pump out a staggering 638 horsepower and 604 pound-feet of torque, while happily spending all day at the track and then comfortably driving you home. The LS9, coupled with a six-speed manual transmission, propelled the ZR1 to a top speed of 205 mph, a figure only supercars could reach at the time.

LS9 cylinder heads aren’t common these days. Finding a brand new pair, forgotten on the shelf, is like winning the LS Lottery.

The LS9 used the same bore and stroke as other 6.2-liter LS engines, but with a forged crank, titanium connecting rods, forged pistons, a block cast with extra reinforcement out of stronger 319-T7 aluminum, and most important to our build: a stout pair of cylinder heads cast from 356-T6 aluminum utilizing extra webbing, thicker decks, and a Rotocast process to make the strongest OEM LS cylinder available. The LS9 heads use the same port shape and intake mounting bolt pattern as the LS3; the same goes for the rocker arms. That means, while the heads are special, they can be easily used on other LS engine builds.

These heads were used on LS9 engines only and offered in limited quantities to purchase through the Chevrolet Performance division.

The LS9 was only in production from 2009 to 2013 for the ZR1s, and during that time, only 4,695 were built. Chevrolet Performance did offer the LS9 as a crate engine and other parts like the bare block and the cylinder heads you see here for a short time, but these were limited in quantity as they were simply left over parts off the production line. Getting your hands on them these days, especially in new condition, is incredibly rare.

The LS9 cylinder heads are a stout pair cast from 356-T6 aluminum utilizing extra webbing, thicker decks, and a Rotocast process to make the strongest OEM LS cylinder heads for boost. Check out the extra webbing on top of each intake runner and each rocker arm mounting pad.

Getting Ahead Of The Game

The LS9 cylinder heads came from the factory with titanium intake valves and stainless steel sodium-filled exhaust valves, but we found our pair completely bare. These heads were lightly damaged on a few of the corners — which you can see in some of the pics — and our local machine shop gave us the go-ahead to assemble them before we bring them in for a quick resurface to fix the dings.

The stock LS9 valves were plenty tough for 638 horsepower or more, but our future boosted LS build will potentially make double that factory rating, so instead of locating rare and expensive stock pieces, we decided to step up to Ferrea’s valve and spring kit that includes premium valvetrain components that can handle our needs.

Ferrea’s 6000 Series Competition Super-Flow valves are made from a two-step slow forging process using EV8 stainless steel with a special heat-treatment and stress relieving process, along with hard chrome stems and friction-welded hard tips.

Our valve and spring kit includes Ferrea’s 6000 series competition valves. These valves are engineered from a premium one-piece stainless alloy and are built to withstand extreme cylinder pressures and high-RPM abuse. Each valve features a hard chrome-plated stem for reduced friction and extended durability, along with a completely redefined swirl polish on the profile and face side, maximizing flow and performance under load. These valves are the same size as stock — 2.165 inches for the intake valve and 1.590 inches for the exhaust valve.

Our Ferrea kit uses PAC dual valve springs engineered to handle cam lifts of up to .700 inches with an installed spring pressure of 150 lbs and an open pressure of 475 lbs.

To match the Super-Flow Competition Series valves, this kit uses PAC dual valve springs engineered to handle cam lifts of up to .700 inches with an installed spring pressure of 150 lbs and an open pressure of 475 lbs. Achieving that level of capability requires precisely matched components, so the package includes CNC-machined titanium retainers, 4140 chromoly alloy spring seat locators, and heavy-duty seven-degree valve locks. Together, these parts ensure the valvetrain remains secure and stable, even when the engine is spinning at high RPM.

The CNC-finished titanium retainers, 4140 chromoly alloy spring seat locators, and heavy-duty valve locks round out the assembly to ensure everything stays locked in at high RPM. — Zeke Urrutia, Ferrea Racing Components

Using The Right Tools

Building cylinder heads at home may seem like a daunting and tedious task, but with some simple hand tools and a couple of specialty tools that don’t break the bank, the process can be done by any at-home wrencher. Which is why, with our LS9 cylinder heads and Ferrea’s valve and spring kit, we decided to save a couple of bucks over letting the machine shop tackle it and decided to tackle it ourselves.

The first tool you’re going to need is a valve spring compressor. These can be found in all different styles and can be ordered online or picked up at your local auto parts store for anywhere between $20 for a simple universal one or a couple of hundred dollars for a professional-grade high-end version. The one we used is from Proform, and is designed to tackle two valve springs at a time by bolting in place of the intake and exhaust rocker arm. This style is popular because it can be used either on the car during a cam swap or on the workbench with bare heads like we have here.

Valve spring compressors can vary from cheap and simple like the one on the left to very expensive professional-grade versions meant for life in a commercial machine shop. The one we used, on the right, is from Proform with a slight modification (Note the right bolt hole cut open) to allow it to be used on all different types of LS heads.

The next tool you are going to need is a valve stem seal install tool. These are a cheap and simple tool, but necessary if you’re looking to assemble cylinder heads yourself. The style of valve stem seal that is used for most aftermarket valve springs is a jacketed style seal that requires you to press the seal onto the valve guide. Doing this without damaging the Viton rubber seal is all but impossible without the proper tool. The one we are using here is from ICT Billet and does a great job of pressing the seal on with a few light taps from a hammer without smashing the Viton rubber into useless Play-Doh.

Putting It All Together

If our LS9 cylinder heads were used, they would be going to the machine shop first to get cleaned up, new guides, and a valve job to get them ready for assembly. But since ours are new off the shelf, a good wipe down to remove any dust or debris from being stored is all we need to do.

The hardened spring seat is required to locate the valve spring and also protect the aluminum head from the alloy steel spring during operation.

While our valve and spring kit from Ferrea is new, too, they need to be wiped down as well. Some parts are sent with protective oils to keep them from oxidizing during storage, most notably, the steel valve spring seats. These seats are sent with a light anti-oxidizing coating that causes the seats to get a yellow and orange residue on them. Sometimes this can be mistaken for rust, but a quick rinse in a parts washer or with soap and water will make it come right off.

Don’t forget to put the spring seats on before installing the seals.

After washing and drying the hardened steel seats, it’s time to place each one over the valve guides with a couple drops of engine oil on top and underneath them. Make sure to place the seats the correct side up, with the inner valve locator lip sticking up. Otherwise, the valve spring will not be properly located, and the valve spring installed height will be wrong.

The seals can’t be installed by hand, but don’t require a lot of force with a hammer. Make sure you press them on with both the seal and tool straight (unlike you see here) or you will ruin the Viton rubber seal.

With the hardened steel seats in place, we grab the valve stem seal installation tool to install the seals . It’s tempting to oil the valve guide or the inside of the seal to make pressing the valve stem seals in place easier, but it is advised not to do this, as this can cause the seal to wiggle loose after enough run time and cause you to do it all over again. We make sure to keep the seal and tool straight during installation and only tap it lightly with a hammer; these can’t be pressed on by hand, but they don’t require Thor’s hammer either.

A thin layer of engine oil or assembly oil on the valve stem before install into the guide is all you need.

Time to flip the heads over to install each valve. A few drops of assembly oil or engine oil on each valve stem is all that is needed before sliding each one into its respective valve guide. If these LS9 cylinder heads were used and received a valve job at the machine shop, we would also take this time to check the valve and valve seat contact patch with some Prussian Blue. But since ours are new, we can now flip the cylinder head back over to install the springs.

Tough Springs For Tough LS9 Cylinder Heads

The dual valve springs can be placed over an intake and exhaust valve stem with the titanium retainer on top before the valve spring install tool is bolted to the rocker arm pedestal pad. Just like the steel seats, we place a few drops of engine oil between the spring and retainer. We torque the two bolts holding the valve spring install tool to the cylinder head to the same spec as the rocker arm bolts: 22 foot-pounds.

With a light smear of grease on the single stud in the center of the tool, we tighten down the nut to compress the two springs. We can start by turning the nut by hand with the 1/2-inch socket, making sure the valve stem is centered in the retainer before fully compressing the springs. Failure to do so can make it difficult or even impossible to install the valve locks without having to remove the tool and start again.

Once the springs are completely compressed, we install two locks on each valve stem by hand, locating them in the groove. This can prove to be a frustrating process sometimes, due to the small size of each lock, making them hard to handle, and struggling to keep them in place during installation without falling out. One trick you can use is a tiny amount of assembly grease or petroleum jelly to act as an engine-oil-safe temporary adhesive to make the lock stick to the valve stem during assembly.

Once the locks are properly put in place, you can back off the nut on the center stud. The springs are now installed and you can move onto the next two.

Now, with each stem held in place in the retainer with two locks, we slowly back the compressing nut off to complete the install. Once we verify that the locks are properly seated inside the retainer, we move on to the rest of the springs. After finishing all sixteen, we now have a pair of brand new LS9 cylinder heads fitted with high-end race-quality guts from Ferrea that can handle anything we plan to throw at them.

Sixteen valves and valve springs installed later, and we have a pair of LS9 cylinder heads ready for our next big boost build.

Ready For Anything

The final build plan for our LS has yet to be decided. Maybe a 6.0 iron block stroked to 408 cubic-inches or possibly an LS/LT hybrid made from the stout L8T iron block and forged crankshaft to make a 401-cube LS. Either would be able to meet our needs to create a 1,000-plus-horsepower LS for the street that will live for a long time, thanks to our new LS9 cylinder heads filled with Ferrea’s valve and spring kit that can handle the heat, boost, and abuse.

3.0-liter Gen-6 Whipple supercharger? A pair of billet-wheel turbos? Regardless of how we decide to build our next 1000-horsepower LS, we now have heads that will be able to handle the pressure.