1,000HP LSX376-B15 Part 1: Building The Long Block At Chevy Perf.

It’s no secret that Chevy’s LS engines are good breathers, so when you force-feed one with a few pounds of boost, its output sprouts like Godzilla’s vegetable garden. Stock, production-vehicle engines are generally capable of handling the boost delivered by basic bolt-on blower kits – anywhere from 5 to 8 pounds, which typically adds about 100 to 120 rear-wheel horsepower.


The components of the rotating assembly are collected and prepped for a series of inspections and measurements to ensure each conforms to the factory specifications. Shown is the forged aluminum piston set, which is used in both the LSX376-B8 and LSX376-B15 engines. When matched with the LS3 heads, they deliver a boost-friendly compression ratio of approximately 9.0:1.

That ain’t bad, but when you’re planning to go after bigger dyno numbers with a high-boost charge, a stronger bottom end is called for because the factory parts simply weren’t designed for that type of performance. In this three-part series, we’re going after big numbers to help our new 1978 Malibu wagon project car “Fugly” get down the quarter-mile in the 9-second range. So thus begins the build of our 1,000+ horsepower, Whipple supercharged behemoth Chevy Performance LSX376-B15. By the way, you can check out the second installment by clicking here, and the third installment by clicking here.

Sure, a Dominator-topped, nitrous-slurping big-block would do the trick, but it’s been done. We’re looking for a challenge and a supercharged LS is the most contemporary way to build big power. And besides, the greater weight balance with an LS power plant – even with an iron block and all the accouterments of the supercharger – will be a valuable advantage for the nose-heavy Chevy.

We’re going to show you nearly every nut and bolt involved in this project in words, photos and video, starting here with the assembly of one of Chevrolet Performance’s boost-ready LSX376B-series crate engines, which will be foundation for our build-up. After this, we’ll show how the engine responds with a large-displacement supercharger, sneaking up on our power goal with moderate boost and the crate engine’s stock valvetrain. Then, we’ll got nuts with higher boost, a Crane Cams solid-roller camshaft and complementing valvetrain, and maybe some other hardcore parts. We’re looking for 1,000+ horsepower and plan to rely on Holley’s new Dominator EFI system to conduct the air/fuel symphony.

After the dust settles in the dyno room, we’ll drop the engine in our Malibu and go get our 9-second time slip. But first things first…

Left: A custom air gauge is used to measure the outer diameter of each piston. The technician rotates the piston within the fixture and air jets are used to determine the diameter, which is recorded on a master file for the engine. The gauge is calibrated every four hours to ensure absolute accuracy. Right: Another air gauge is used to measure the pistons’ pin bores. In all, there are 15 air gauges used throughout the engine assembly, taking measurements down to 0.00001-inch. Again, every measurement is recorded in a master file for each engine.

Inside the LSX376B Crate Engines

Chevrolet Performance developed the boost-capable LSX376B-series engines a couple of years ago with the express purpose of offering economical long block-style assemblies that are ready to accept the supercharger or turbo system of the builder’s choice. There are two versions – the lower-boost LSX376-B8 (part number 19260831) and higher-boost LSX376-B15 (part number 19299306).

With the LSX376 ‘B’ engines, we’ve created affordable foundations for supercharged or turbocharged power that fit just about every budget. – Dr. Jamie Meyer

As their names imply, the LSX376-B8 is rated to about 8 pounds of boost and the “B15” is good for about 15 pounds or so. Each uses a mix of purposeful high-performance components and production components, which helps keep down the price. They didn’t skimp where it counts, however, such a forged steel crankshaft on the “B15.” The other important component of each assembly is a set of forged aluminum, low-compression pistons, which are essential for longevity and staving off engine-killing detonation. If you simply bolt a blower onto a production engine, you’ll be dealing with compression of around 10.5 or 11.0:1 – or higher – and hypereutectic pistons.


The LSX376-B15 engine uses the tough connecting rods from the Camaro ZL1’s LSA engine, which were designed from the outset for a supercharged engine.

Left: The LSA rods are delivered to the assembly line as single pieces, then the cap is carefully snapped off, creating a perfect, puzzle piece-like fit when it’s installed on the engine. Right: Like the pistons, each rod is measured with a custom air gauge tool, which measures the small and big ends simultaneously. This one passed with flying colors and is headed for our project engine.

Perhaps just as importantly, the engines use LSX-LS3 cylinder heads, which are based on the high-flow, rectangular-port design of the production LS3 engine, but with a six-bolt head bolt design matched with the LSX block’s six-bolt provisions. It significantly enhances clamping strength for the heads, providing – along with standard multi-layer steel head gaskets – exceptional cylinder sealing under high boost pressure. That’s just what our project engine will see when we get our greasy mitts on the crate engine.

“Chevrolet Performance engineers developed the LSX Bowtie block and LSX cylinder heads specifically for the rigors of extreme performance,” says Dr. Jamie Meyer, Performance Marketing Manager for Chevrolet Performance. “With the LSX376 ‘B’ engines, we’ve created affordable foundations for supercharged or turbocharged power that fit just about every budget. Of course, the blower, fuel system and other necessary components are up to the customer, but with their durable forged components, six-bolt head clamping and lower compression, these engines deliver a lot of boost for the buck.”

The heads also offer tremendous airflow attributes, too, which is just what we want for an engine that will have plenty of air crammed through it. They have rectangular ports similar in design to the LS7 design, with large, 260cc intake ports. The LSX six-bolt castings also feature a little more meat on the bone in strategic areas to support additional port work. We don’t know if we’ll hog ’em out further, but it’s good to know the heads can handle it.

Left to Right: The roller lifters are measured, too – and not simply to confirm their diameters. Out-of-round and taper is measured, as well. With the camshaft, the part number is verified, the part number is recorded in the master file and then the journals are measured with another air gauge. Out-of-round and taper are also determined. With all of the respective measurements completed, work begins with building the rod-and-piston assemblies. A cast iron LSX Bowtie Block with the regular-production 9.240-inch deck height is the engine’s foundation and is delivered to the assembly line already honed and cleaned. After an inspection, it undergoes a wash to remove residual oil or grease and is then blown dry with compressed air. The main bores, cam bores, damper inner diameter and other journals are then measured with air gauges.

We’re also told these crate engines use the latest version of the LSX block, which was revamped recently to improve strength and durability, particularly under boost. That’s an assuring thing to keep in mind as we head for four-digit horsepower territory on the dyno.

Building For Boost

LSX376-B15 PN 19299306 Specs

  • Power: 450HP at 5,900 rpm, 444 lb-ft. of torque at 4,600 rpm naturally aspirated
  • Displacement: 376 CID, 6.2L
  • Bore x Stroke: 4.060” x 3.620”
  • Compression Ratio: 9:1
  • Block: LSX Cast Iron with 6-bolt cross bolted main caps
  • Crankshaft: Forged 4340-steel, LSX 8 bolt flange
  • Connecting Rods: Forged Powdered Metal Steel
  • Pistons: Forged Aluminum
  • Camshaft: Hydraulic-Roller Tappet
  • Cam Specs .560” Intake / .555” Exhaust @ .050”: 210 deg. Intake / 230 deg. Exhaust, LCA: 121 degrees
  • Cylinder Heads: Aluminum LS3 Rectangular style ports, Combustion Chamber: 68cc
The LSX376B-series crate engines are assembled at a specialized facility in the Detroit area, which blends the best of hand-assembly and production-line techniques. Every component associated with the rotating assembly the respective holes they fill in the block are mic’d with ultra-precise air gauge tools and their specifications recorded in a master file for each engine. Think of it as high-tech blueprinting.

Computer-controlled and calibrated torque wrenches ensure consistency with every engine, too, but they don’t replace the eyes and experience of specially trained builders who guide each engine from start to finish. There are only four stations involved with each engine’s assembly, with a single builder at each one responsible for specific tasks. In the first station, the rotating assembly and engine block are inspected, measured and prepped for assembly. At the second station, the bottom end of the engine is installed and at the third stage, the heads and other top-end parts are added. The final station is an inspection stop, where each engine subjected to a roster of checks, including leaks, compression and oil pressure.

Unlike some other Chevrolet Performance crate engines, the LSX376B-series engines do not come with an intake system or oil pan, which helps keeps the cost down and creates less waste – after all, who needs a production-style intake manifold if you’re going to drop on a 4.0-liter Whipple twin-screw compressor? And with LS engines being thrown into so many different cars these days, what good is a production oil pan that’s just going to be removed or sliced up anyway? We’ll definitely need a custom pan for our Malibu. Custom headers, too – but more on all that in our next installments of this high-boost project.

Until then, check out the photos we took inside the assembly facility and learn more about what goes into these specialized crate engines. We’ll definitely be putting out LSX376B15 to the test soon!

Assembly Photos and Captions


A forged steel crankshaft with a 58X reluctor wheel is carefully lowered into place, but prior to installation, the rod and main journals are measured in four places to calculate out-of-round and taper. Also, the crank’s snout and the damper’s internal diameter are measured to calculate the interference fit.

In goes the camshaft. For our “B15” engine, it’s the LS7’s high-lift hydraulic roller, which has a pretty wide 121-degreee lobe separation angle a hydraulic roller, along with 0.558/0.558-inch lift and 211/230-degrees duration specs.

With the crankshaft and camshaft in place, the roller timing chain setup is installed, after which the high-volume, wet-sump oil pump from the LSA production engine is installed on the crank snout.

The piston assemblies are slide into place after the rod bearing received a coat of oil. Guide tools threaded onto the ends of the rods and a piston ring compressor ensure an easy, damage-free installation. The connecting rod caps are then torqued down to 64 ft-lbs.

With the engine upright, the roller lifters are carefully tapped into place and their respective keepers cinched down.

It takes a lot of pressure to drive on the damper onto the crank snout and a hydraulic cylinder is used for the task. Then, the damper bolt is tightened with a 6:1 gear-reduction tool, because of the high torque rating – 37 ft-lbs plus 140 degrees.

Both the LSX376-B8 and B15 engines use multilayer steel cylinder head gaskets that offer exceptional cylinder sealing for supercharged and turbocharged engine combinations.

The engine breathes through Chevrolet Performance’s LSX-LS3 cylinder heads, which are based on the high-flow, rectangular port design of the standard LS3 head, but with a six-bolt configuration that greatly enhances the clamping strength when compared with production-style four-bolt heads. They also feature large, 260cc intake ports.

The LSX-LS3 heads have 68cc combustion chambers and 2.160-inch hollow-stem intake and 1.550-inch solid-stem exhaust valves. The valves are held at a 15-degree angle.

The valvetrain comes next and includes LS3 pushrods and a set of LS7-style 1.7-ratio rocker arms, which feature and offset design on the intake-side arms. They’re torqued down to 30 Newton-meters.

A valley cover caps the engine and essentially completes the engine assembly. The LSX376 “B” engines are delivered without an intake manifold to make it easier and more economical to accommodate a blower or turbo. And because vehicle installations very so wildly, they’re delivered without an oil pan, too. A dust cover is installed over the crankshaft.

After the engine is assembled, it’s moved to final-inspection station, where it is leak-tested by pumping the water passages with about 20 psi of compressed air. The engine is also primed with warm oil to validate oil pressure and the compression is checked. From here, it will be shipped to our dyno facility, where the next stage in our project will begin with the supercharged installation. Stay tuned!

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About the author

Barry Kluczyk

Barry Kluczyk has been writing about and photographing cars for more than 20 years, starting with test-drive columns he launched at Central Michigan University’s newspaper. Along with serving as the editor for several magazines and contributing to countless more, he’s also authored three automotive books to date. Barry is an active enthusiast who has owned more than 50 cars over the years – and is always looking for the next project. He grew up in the “Thumb” area of Michigan, northeast of Detroit and lives in the Motor City’s northern suburbs, near legendary Woodward Avenue.
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