This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

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In an age where turbochargers and superchargers dominate high-performance vehicles, high-horsepower, normally aspirated engine builds are frequently bypassed in favor of the big power headlines offered by their boosted siblings. It doesn’t have to be that way. We all know the three basic paths to horsepower: boost, rpm, and the old standby, cubic inches. How you get there is any man’s choice, but cost, reliability, and packaging strongly influence the decision process. Stock drag racing classes are currently enjoying a renaissance supported by factory supercharged cars, but the cost of those killer packages puts their new level of performance well out of reach for many working-class buyers. There is still respite for naturally aspirated cars, and High Performance Connection along with Horsepower Research is leading the charge with General Motors’ LT1 engine platform.

For a street/strip package, high RPM isn’t necessarily the best choice, as it typically diminishes low-end torque and breaks expensive parts. Boosted applications incur the added expense of packaging intercoolers and associated support hardware within increasingly crowded and difficult-to-cool engine bays. Increased displacement addresses both of those concerns head-on and is capable of delivering superb performance without the complication and added expense of turbochargers, superchargers, nitrous oxide systems, or parts-killing engine speeds that aren’t practical in a street-driven package.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

GM blocks feature world-class 319–T7 aluminum castings, robust architecture with 6-bolt mains, and deep crank-in-block construction. Note the breathing ports on either side of the mains to help equalize pressure in the sump. The 6.2-liter blocks incorporate all the same features, and HPR can build you one either way.

The gearheads at HPC wanted to test their premise that increased displacement could serve up a significant performance increase without the added expense of supercharging and its associated complexity. The goal was to add maximum bang for the buck to an existing platform and see how well it delivered. They are well-connected with their colleagues—Erik Koenig and Anthony Forney at Horsepower Research in McKinney, Texas—so they asked them to prepare the short block while they procured the CNC-ported cylinder heads from Competition Induction Designs in Cottage Grove, Minnesota.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

Stroke length on this crankshaft is 4.350-inch, making the engine undersquare. A custom K1 Technologies crankshaft is modified by Shaftech with six counterweights to help stabilize the undersquare assembly, which experiences greater stress from higher piston acceleration. The rod journals are ground to accept small-journal Chevy rod specs.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

Initial testing exceeded 700 rear wheel horsepower.

The test mule was HPC’s LT1-equipped 2018 Camaro SS 1LE, an already-potent 6.2-liter factory package rated at 455 horsepower and 455 lb-ft of torque at 4,400 rpm. The supercharged ZL1 version is factory rated at 650 horsepower at 6,000 rpm. HPC’s Elie Bejjani wanted to modify the normally aspirated LT1 engine to exceed the supercharged ZL1 rating using displacement only to reach his goal. They had already built the world’s largest LS engine for a previous project, so they set out to build the largest LT1 engine at nearly 478.7 cubic inches, or as they refer to it, the 480-inch LT1. The result of careful planning realized an initial test of 705 horsepower on E85 pump gas.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

The block was precision-machined and fitted with eight Darton sleeves, which took the bore size out to 4.185-inch. While the engine is undersquare, in this instance, the bore size is not a detriment because it easily accommodates the chamber size on the cylinder heads. In this application, the piston squirters are blocked off.

Increasing the displacement by more than 100 cubic inches would seemingly take the stock cylinder heads right out of the equation, and it does, but surprisingly the development program ended up using Competition Induction Design castings ported by Greg Good Cylinder Heads to achieve spectacular results—from a cylinder head with intake ports smaller than the factory LT1 ports. CID utilizes its proprietary-design, GEN V LT1, 6-bolt castings, and Good’s CNC porting program for the HPC project ended up with only 280cc intake ports, a full 17cc smaller than stock 297cc factory heads. How is that possible, you ask? Well, CID’s philosophy and Good’s handiwork rightly focused on increasing port velocity and thus cylinder filling along with subtle chamber mods to optimize atomization with the direct injection engine. These efforts—combined with appropriate cam timing—deliver a denser, more homogeneous charge packing more power into every combustion event.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

Callies Compstar Ultra H-beam rods, PN CSC6125CS2A2AH are fitted with ARP 2000 rod bolts and shot-peened to provide the mirror surface treatment. They are 6.125-inch on centers with small journal Chevy big end and use a .927-inch diameter wrist pin.

CID’s new heads offer up 25-percent-thicker decks and revised water jackets to strengthen the casting, which allows the use of heavier and larger diameter valvesprings to support valvetrain stability and further provides greater rigidity to accommodate higher cylinder pressures. Material increases around the already-modified intake and exhaust ports permit port modifications and flow results not possible within a factory casting. The rocker stands are tied together as one full-length rocker stand, which provides the option for the end-user to install aftermarket shaft-mounted rocker systems if desired. The heads are finished with CHE precision bronze valve guides and CHE iron valve seat inserts. They accept LT1 and LT4 intake bolt holes and can be ordered with LT1 chambers, LT4 chambers, or the Greg Good-developed CNC chambers that are the same size as a factory LT1 head.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

Wiseco custom 2618 alloy pistons configured to HPR specs with direct-injection crowns are treated with Wiseco’s ArmorGlide® coating for friction reduction. These pistons feature .200-inch-wall pins and Spirolox® pin retention. Wiseco already makes forged replacements for standard L83 engines, and they can manufacture custom direct-injection pistons for any bore size and pin height required.

The as-cast intake port flows 330 CFM at .500-inch valve lift with nearly 360 CFM available at .800-inch lift through the factory intake valve size and location, but with almost 30cc less port volume than a ported factory casting. With its new, improved port shape, the CID intake port incorporates a marginally smaller opening than a factory head, and the exhaust port is also substantially improved, flowing 270-plus CFM through the factory exhaust valve size.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

Here is the tiny .9mm Total Seal ring ready for gapping in the cylinder bore. It is a barrel-faced nitrided steel top ring, supported by a .9mm Napier second ring and a 2mm oil ring.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

The lower end is a robust combination of top-quality forged and billet components selected to support the large displacement and high output of this engine. This combination has proved to be reliable and trouble-free.

The smaller port head was initially designed to support a head and camshaft package developed to make 600 rear-wheel horsepower. When applied to the larger displacement 480-cid engine with more cam and an MSD intake manifold, the package exceeded 700 horsepower at the rear wheels. Since then, Good has performed more work on the exhaust ports, and this naturally aspirated engine is currently supplying 771 rear wheel horsepower in the Camaro. That’s probably 850-plus at the flywheel depending on drivetrain losses, or close to 1.8 horsepower per cubic inch.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

Wiseco’s direct-injection pistons are fitted at a positive deck of .015-inch and .051-inch compressed thickness Cometic 4.190-inch MLS head gaskets, PN C5319-051, seal the chambers.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

The cylinder block for this build is a GM L83 5.3-liter aluminum block (PN12620290 if purchased new). This block offers extra beefy construction to accommodate the installation of Darton sleeves that would take the bore size out to 4.185-inch. HPR advises that they can also accomplish this with the 6.2-liter block as well. Quicker availability of the 5.3-liter block guided their selection for this particular build.

When given the option of supporting the large-displacement engine with larger, lazier intake ports or smaller higher velocity ports and improved cylinder filling, the choice was clear. It must also be remembered that this engine sports a significantly larger bore size, hence the need to maintain air velocity and optimize pressure recovery as the air enters the cylinder.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

The CID aluminum cylinder LT head is specific to the direct-injection LT1 engine. According to head porter Greg Good, airflow quantity (CFM) and port volume have been and remain the main criteria for choosing a head. That’s the cylinder filling part of the intake port’s job. As a rule, larger port volumes reduce flow velocity and compromise mixture quality unless engine speed is substantially increased.

(Left) On the LT1 engine, the direct-injection strategy means that all of the air/fuel atomization has to take place inside the cylinder in a very short time frame. Good used the CID cylinder head to incorporate its smaller volume intake ports and higher port velocities to ensure maximum cylinder filling. He says the factory ports are too large for efficient filling in the engine’s optimum operating range. (Center) The exhaust port exit appears big because of its square shape, but the angle of the port/header flange gives that illusion. The port cross-section also remains on the conservative side with just enough to accommodate the increased flow from the engine’s higher output. (Right) Higher port energy entering the combustion chamber also helps improve mixture quality, which has minimal time to occur in a direct injection engine. Good focuses his porting efforts to optimize how the air behaves after it enters the cylinder.

These smaller ports are highly effective, providing ideal port velocity in the engine’s functional rpm range. Their high velocity also supports a later intake closing event to promote additional cylinder filling well after BDC for increased volumetric efficiency. The intake port floor is nearly an inch higher than an LS head and four-tenths longer for an ideal line-of-sight to the valve. The casting is exclusive to Competition Induction Design, but it uses the OEM 2.125-inch chromium nitrided intake valves and the 1.595-inch hollow-stem exhaust valves used in the current factory ZL1 supercharged engine. The compression ratio is set at 13:1, and the engine burns E85 fuel.

The short block prepared by Horsepower Research is based on a GM L83 5.3L aluminum block that was chosen for its extra beefy casting and easy availability. The larger 7.8-liter displacement (478.7-cid) required all eight cylinders to receive new Darton sleeves, which were then finished to 4.185-inches in diameter. The crankshaft is a 4.350-inch stroke K1 crank modified by Shaftech with six counterweights.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

With power revisions ramping up to 772.8 rear-wheel horsepower, the LT1 engine was transplanted into a new 2020 Camaro with a ten-speed automatic transmission. 

The Total Seal ring package features a barrel-faced nitrided steel .9mm (.035-inch) top ring, a .9mm Napier second ring, and a 2mm oil ring. The ring pack sits high on the piston in close proximity to high combustion temperatures; hence the pistons are treated to Wiseco’s ArmorGlide protection for superior resistance to detonation and micro-welding. All of these components spin on Federal-Mogul bearings, and the whole assembly is anchored with ARP fasteners, including ARP 2000 rod bolts. Lubrication is accomplished with the 2018 OEM factory wet-sump oiling system. A factory dry-sump system is being contemplated when the engine is moved into a new 2020 Camaro drag car.

This Wild Naturally Aspirated 478 Cubic-Inch LT1 Engine Makes 778 RWHP

This view shows what incoming air sees exiting the throttle body. The plenum is sized to accommodate the engine’s increased displacement, and the manifold was ported by Greg Good to achieve high port velocity entering the cylinder heads.

This LT1 engine is a work in progress, and the guys are working diligently to wring every last bit of performance from the engine. Significant gains were achieved by switching to a Holley High Ram intake with a custom-built lid, an adapter neck with a larger 103mm throttle body, and a Snow Performance methanol/water injection plate. The engine is well north of 850 horsepower and delivers more than 775 horsepower at the tire. You too can gain this kind of performance for your naturally aspirated car now that they have paved the way forward.

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