Video: Inside of NRE’s 1200-HP 260-CI LS After An Hour On The Dyno

After posting an article showcasing a twin-turbo LS engine making a five-minute wide-open throttle dyno pull from Nelson Racing Engines, Tom Nelson went on to complete the durability testing of that engine by making 11 (yes, eleven) additional five-minute, wide-open, full-boost, 7,000-plus-rpm pulls on the dyno. That makes for a total full-tilt time on the dyno of just over an hour. An hour of some of the most intense torture on the engine we’ve ever seen on a dyno.

The engine not only survived the test, but did so with flying colors, as we’ll talk about in a minute. In addition to the test, Nelson opened up about the components chosen for this project, and some of the secrets to making this engine combination survive such harsh conditions without the slightest misstep.

Surprisingly, the parts, while custom, aren’t all that exotic (except for maybe the water-cooled headers). Surprisingly, most of the components are products that you can call and order with the normal wait-time for a custom part. No crazy exotic materials; no secret-squirrel components. Nelson pulls back the curtain and shares the engine’s details.

The Heart of it All

At the core of any engine is, of course, the block. “The block is the foundation of everything,” says Tom Nelson. Without a solid foundation, every other component used in a build is ultimately at the mercy of the strength of that foundation. The Chevrolet Performance LSX block is a stout foundation, as we’ve shown many times over. The cast iron block is not only strong, but also has some extra features that are beneficial to Nelson.

“It has two extra head bolts per cylinder, which will help hold the head down under high boost conditions,” explains Nelson. Of course, no engine block on the shelf will have all of the little tricks Nelson relies on for a build of this caliber, so he still had a laundry list of modifications to make.

“We’ve actually gone into the mains, and drilled through the main oil galley and machined a boss so we can put little .026-inch jets that will shoot oil at the bottom of the pistons,” Nelson reveals.

The only real “exotic” part on the build is the set of water-cooled turbo manifolds. By running a double-wall primary tube, water can be flowed around the main primary tube to help keep the temperatures of both the manifold and the turbos in check.

“When that piston is sitting there glowing red because it’s got 1400-degree combustion temperatures on the top of the pistons for half an hour, we shoot oil onto the bottom of the piston to try and cool it off and keep it alive.”

In addition to machining the block for oil squirters, Nelson also gives the block’s deck some special treatment. “We’ve cut grooves into the block deck – what we call o-ringing the block. We cut the groove at .048 inch thickness, maybe .031 inches deep. Then we use piano wire in there, which is stainless steel and really hard,” says Nelson.

“It’s a bitchin’ wire to use for o-ringing. It’s actually really cool – not many people know it’s piano wire. It sticks out of the deck and compresses the head gasket.” While O-ringing the block is definitely nothing new, using piano wire is a new one to us.

The iron LSX block was chosen, in part, for its two extra head-bolts per cylinder. NRE has also machined a groove in the deck surface for a piano-wire O-ring, to help further contain compression under harsh conditions and insane cylinder pressures.

Opening Up The Heart

Inside the block, Nelson uses some high-end components as you might expect. If you’ve done any research on how to get 260 cubes from an LS engine, you know the parts are going to be custom. When it comes to custom crankshafts, you know that means billet. “We’re running a billet Callies crankshaft in this. It’s fully counterweigheted and we’ve knifeedged the crank to chop up the oil,” Nelson relays.

Obviously one of the main benefits of aftermarket LS components is the ability to generate significant displacement without a lot of effort, but as we pointed out in the previous article, this engine is being built to take advantage of a displacement rule. “It’s only 2.725 inches of stroke. That sounds kind of odd for an LS, but we feel that we’re going to demolish the field with this little rulebook choice here.”

To compliment that 2.725 inch stroke, Nelson went with a 3.890-inch bore, which is .008 under the standard LS1/LS6 bore, and comes out to 259.09 cubic inches. Of course, regardless of bore size, the slugs for this engine were going to be completely custom pieces. For that, Nelson turned to JE Pistons.

“We designed this piston with JE Pistons to withstand this kind of boost. It wasn’t designed for light weight, it was designed for strength. One of the things we did was run a full skirt on this piston,” explains Nelson.

“Also, we designed the crown of the piston to be .330-inch thick. For example, a normal turbo piston is about .200-inch. So, we’ve added an extra .130 inch to the crown thickness to help it withstand the heat this thing is going to see.”

Obviously, getting an LS down to 260 cubic-inches is a tall task. To do that, Nelson spec'ed a billet 2.725-inch crankshaft and 3.890-inch pistons. The JE pistons are built to survive in a severe-duty application, with an extra .140-inch of crown thickness and a full skirt design. The Callies billet crank is fully counterweighted with two center counterweights, all of which employ Callies knife-edging to help reduce windage and drag.

The process of connecting the crankshaft to the piston also got a dose of the mad scientist treatment. “I took a BBC rod, which has a .990 pin, and grafted that into the piston. It’s a 6.535[-inch long] rod, and that’s going to make a huge difference in strength having a big block rod in in small-block LS. Then, we’re using an H13 tool-steel wrist pin with a .225-inch wall. This thing is super thick,” Nelson says.

Keeping the crank and rods spinning at sustained high-RPM is a task that you might expect to fall to something super-trick. Instead, Nelson opted for the tried-and-true solid performer – Clevite H-series main and rod bearings. That says a lot when the only off-the-shelf part in your engine, is the bearings.

The Top Floor

Moving up to the top end, there aren’t a whole lot of details revealed on the cylinder heads, but by paying attention, we were able to discern a few things. One, is that they are Mast Motorsports castings, and two, is that they are cathedral-port heads, which is interesting because you’d expect a LS3 or even LS7 style head in this kind of application.

While not disclosing valve sizes, Nelson does say he’s using an Inconel exhaust valve in the setup. “For me, on a turbocharged engine, Inconel valeve are a must. With a regular valve, they get really hot, and then get soft and end up tuliping. So you always want to use Inconel on the exhaust valve,” he relates.

While official details on the heads used on the engine are scarce, we are able to determine that they are a variant of Mast Motorsports cathedral-port castings, with stainless intake and Inconel exhaust valves. This image also shows that the ports and chambers have been completely CNC machined as well.

Again, while not disclosing the specifics of the valvetrain, Nelson did discuss some of the engineering that went into the camshaft, saying: “The camshaft is truly the brain of the engine. We designed lobes specifically for this engine. This engine is going to run at high-RPM for a long time, so we wanted the lobe to be smooth and gentile so the valvespring can easily control it.”

Pumping the Lifeblood

In a situation such as the one this engine will spend most of its life in, a proper oiling system is essential. That obviously means a dry-sump system will be the configuration of choice. “A dry-sump is super-important because in an engine where you’re going to be pounding on it full-throttle for the whole time, you’re going to need good oil on those bearings,” Nelson says.

“We’re using an all billet dry sump by Daly Engineering. Daly has separated each main into its own scavenge area. What’s unique is that there are no lines from the pan to the pump. The pump mounts directly to the pan, and they have bored oil passages in the pan itself to feed the pumps.”

The Daly Engineering dry-sump pan (left) seals each main area into it's own individual scavenge section for maximum efficiency. The air/oil separator turbine (right) prevents any aerated oil from making it directly back into the system. Instead, diverting it to the tank, allowing it to de-aerate.

Nelson also worked with Daly to incorporate an air/oil separator into the pump assembly to minimize as much oil aeration as possible. “What happens is when you are revving the engine and the oil pumps are sucking in that oil really hard, it mixes with air and it starts frothing. Air is not a good lubricant,” explains Nelson.

“That’s going to make a huge difference, in my opinion, on how long this thing will live. I feel like not enough people discuss oil aeration, so hopefully we’re inspiring some people to think about that.”

Inspecting the Wear

At the end of the twelfth five-minute dyno pull, Nelson decides to pull the oil pan and inspect the components to see what kind of wear could be observed. “I couldn’t believe how cherry everything was. I’m not even going to replace the bearings The H series bearings in the rods and mains don’t even look worn. They’re perfect,” says Nelson

With the dyno trials complete, the only thing left to do is to run the engine in-class and see what happens. Nelson is banking a lot on the small-displacement twin-turbo combination being able to outrun the significantly larger naturally aspirated entries in the class. While they know they are making more steam on the dyno, their combination is also unproven as of yet, making it the underdog.

“There are a lot of little things we’ve engineered in the engine, to try and make it all work,” says Nelson. “We’re either going to be crying or laughing at the end of it, or maybe both.”

After a full hour of wide-open throttle, full-boost,, and 7,000-plus rpm, Nelson pulled the main and rod caps off to check the bearings. Surprisingly, their condition belied the torture they had just been through, with Nelson commenting, "I'm not even going to change them!"

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About the author

Greg Acosta

Greg has spent seventeen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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