Giddy-Up 409 — Modernizing A Chevrolet W-Series 409 Big-Block

Giddy-Up 409 — Modernizing A Chevrolet W-Series 409 Big-Block

The big-block Chevrolet that we all know and love made its debut in 1965. However, as its Mark IV nomenclature suggests, there were three predecessors. Although only separated by seven years, the big-block Chevy’s granddaddy is the W-series engine. The 348 was the first big-block engine Chevrolet introduced, and was soon followed, with additional bore and stroke (4.310 inches x 3.500 inches) upping the displacement to 409 cubic inches in 1961.

While historically significant, the engine is largely obsolete in the modern world, thanks to its goofy combustion chamber design. Instead of the traditional setup, with a combustion chamber in the cylinder head housing the valves, the valves were flat against the cylinder head deck, and instead, a 16-degree wedge combustion chamber was formed by the top of the piston and the angled block deck.

With a traditional 90-degree cylinder bank angle but a 74-degree deck angle (relative to the piston centerline), a distinctive 122-degree included deck angle is created. We see something similar in modern VR6 engines, and while it was successful there, in the W-series application, it proved to be the engine design’s Achilles heel.

However, one sure way to get the Dorton brothers — Keith and Jeff — of Automotive Specialists interested in a project is for it to be off-the-wall and challenging. This is exactly what modernizing a W-series 409 is. Thankfully, Jeff Huneycutt of The Horsepower Monster was able to capture the project and document this interesting oddity.

Here you can see the Achilles heel of the W-series engines — the goofy deck angle. While the engine's cylinders are in a traditional 90-degree V configuration, the deck is offset by 16 degrees, making for a 122-degree deck angle. As you can see, that makes for a wedge-shaped chamber between the deck of the cylinder head and the crown of the piston.

An Ancient Foundation

While this engine design is approaching its 65th birthday, and only had an eight-year production life, surprisingly enough, an aftermarket block is on the market today. The version Dorton used is a cast-aluminum 9.600-inch deck height variant from Bill Mitchell Products. Besides being lighter, the BMP block incorporates billet four-bolt main caps as opposed to the factory two-bolt caps, and additional gusseting throughout the block, for additional strength.

Since the BMP block uses the standard big-block Chevy main size instead of the smaller W-series main size, a set of narrowed BBC main bearings from ACL were used. That also means that a standard, off-the-shelf big-block Chevy crank could be utilized as well. Dorton opted for a forged Molnar unit with a 4.00-inch stroke.

Here you can see the unique piston design required to work with the weird chamber. The one upside to the design is not needing a ring compressor when installing the pistons and rings into the bore.

Forged Molnar H-beam connecting rods are used, along with ACL rod bearings to secure the pistons to the crank. Ross Racing was tapped for the big 4.500-inch domed 409 pistons measuring 69.5 cc. The physically large pistons are attached to the connecting rods via a stout .990-inch wrist pin. The new bore and stroke work out to 509 cubic inches, with a compression ratio of 9.2:1

A steel Moroso oil pan, measuring 6.5 quarts, seals up the bottom end and features a windage screen and trap-door-baffled kickout in the sump to help mitigate oil motion. An ATI Super Damper is used to kill any torsional harmonics in the build, finishing off the bottom end.

No, that’s not a diesel cylinder head, but rather an Edelbrock 409 casting. The chambers, if you can call them that, are just enough recess to house the valve head and the spark plug. The Edelbrock head’s recesses measure a scant 16 cc.

The Flat Heads

The 409’s cylinder heads aren’t a flat head in the traditional sense, but rather, have an almost completely flat deck, like you would find on a diesel engine. For this build, Dorton opted for a set of 409 heads from Edelbrock, which have been CNC ported by the 409-specialists at Lamar Walden Automotive. They feature 2.190-inch intake valves and 1.720-inch exhaust valves, with a 220 cc intake runner (before CNC porting). The valves are controlled by a set of dual valvesprings offering 140 pounds of seat pressure, and 400 pounds when open.

A Lamar Walden Automotive camshaft was chosen, and features .632 inch of valve lift on the intake, and .636 inch on the exhaust with 244 degrees of duration at .050 inch on the intake and 253 degrees on the exhaust, with a 108-degree lobe separation angle. The camshaft also has a 4/7 firing order swap built into it.

A set of tie-bar Johnson hydraulic roller lifters translate the camshaft’s rotation into vertical movement. Because the lifter bores on the BMP block are spread .100 inch from stock, standard BBC rocker arms are out of the question. Instead, a set of 1.75:1 pedestal-mount aluminum roller rockers from Lamar Walden, designed specifically for this application were used. 5/16-inch-diameter, .080-inch wall-thickness pushrods were used; 8.050 inches long on the intake and 8.350 inches long on the exhaust.

Because the Bill Mitchell Products block features lifter bores that are spread .100 inch farther apart than stock, standard big-block Chevy rocker arms won’t work. However, these pedestal mount rockers from Lamar Walden Automotive are designed for exactly this scenario.

A Modern Finish

Since the whole point of this project is to truly modernize this first-gen big-block, port EFI was the call. That required a one-of-a-kind Hogan’s intake manifold and set of fuel rails. An Accufab oval throttle body was fitted to the manifold, and 76 lb/hr fuel injectors were fitted into the runners. A Billet Specialties front-drive setup was employed to run all the accessories, and a set of cast aluminum valve covers top the combination.

An MSD Pro Billet Dual-Sync distributor will not only distribute the spark from the MSD 6 EFI ignition box and coil, but also act as a camshaft position sensor for the Holley EFI Dominator ECU. Jeff Dorton will be tickling the keys to optimize the tune in the ECU.

This might be the most modern first-gen big-block Chevrolet anyone’s ever seen. The intake manifold is a completely custom piece from Hogan, in order to incorporate modern port-injection EFI.

On the dyno, the engine was saddled with a set of headers that were too small for the application, due to supply-chain issues. Between that, and the mild street-grind camshaft, the fact that it made well over 500 lb-ft of torque at the start of the dyno test was impressive. The final numbers on the graph were 526.2 horsepower at 5,500 rpm and 557.2 lb-ft of torque at 4,200 rpm.

Besides the obvious shortcomings in the engine design, which limited upper-RPM performance, Huneycutt points out that the amount of ignition timing the engine required (44 degrees) shows just how inefficient the W-series engine design is. Even though modern parts made a significant improvement over the factory pieces, it’s proof that modern technology can’t overcome the physical limitations of a poor design.

Here you can see, that the curves are stout, but that the engine is done by 5,800 rpm. 526 horsepower and 557 lb-ft from a 507 cubic-inch big-block isn’t earth-shattering by any means, but for its intended application, it’ll get the job done.

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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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