Except for the iconic valve covers, Automotive Specialists’ new-age 409 build hardly bears any resemblance to the classic big-block. But this engine still has the combustion chambers in the cylinder bores and is still very much a W-series engine at its core—just with 526 hp!
Automotive Specialists Updates the Classic 409 for a New Millennium
When it comes to big-blocks, sightings of Chevrolet’s W-series engines are getting more and more rare out in the wild. But historically, they are incredibly important.
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The W-series marked the first big-block offering for Chevrolet, which needed more power and torque for the increasingly heavy cars and trucks it was producing. The 348ci version came first and started showing up in 1958.
But that was the 348. Nobody sings great songs about the 348. The engine that everyone cares about when you’re talking about W-series engines is the famous 409. You know, the one that the Beach Boys sang about in the song … uh … “409.” Yeah, it’s catchy, but it ain’t deep.
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The foundation for this build is an aluminum 409 block from Bill Mitchell Products (BMP). BMP says that even with the billet steel main caps, this block weighs in at just 150 pounds. Aftermarket support for the 409 is pretty thin, so to make life easier it can accept standard big-block main and rod bearings, crankshaft, timing set, oil pans, distributor, cam bearings, and other components. Check out the iconic 74-degree deck angle (most engines have a block deck that’s 90 degrees to the crankshaft centerline).
Anyhow, the 409 was the real performer. Although it didn’t have a long production life— appearing in ’61-64 model years—the 409 was one of the first American-made engines to break the 1 horsepower per cubic inch barrier when it was rated at 409 hp and 420 lb-ft of torque in 1962 thanks to dual Carter four-barrel carbs.
By 1963 that number improved to 425 and 425 with a solid flat tappet valvetrain. And that’s not even counting the infamous Z11 variant that was punched out to 427 ci with 14:1 compression and was rumored to produce nearly 500 hp. Of course that was simply a homologated drag race engine and only a tad more than 50 were ever sold to the public.
The block has the larger 2.750 big-block main journals (original 409 is 2.500) so we were able to source a stroker big-block crank from Molnar Technologies. Stroke is now 4.00 inches, which is a full 1/2-inch longer than the 409 left the factory with.
The 409 and 348 are quirky engines because the combustion chamber isn’t in the cylinder head but is in the block. The deck of the block is 74 degrees to the centerline of the crankshaft where almost all other engines are 90 degrees. That creates a wedge-shaped void between the top of the piston and the deck of the cylinder head for a combustion chamber.
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Because of this weird arrangement, the W engines typically create a lot of swirl in the combustion charge for lots of low-end torque, but the vertical valve arrangement makes it hard to develop a port that moves lots of fuel and air efficiently.
This block should be significantly stronger than the original casting, even if it is aluminum. One major factor is the billet steel main caps. The 409 only came with two-bolt mains, but the BMP block has four big 1/2-inch fasteners on all five caps.
Chevrolet’s engineers apparently knew early on that they were at a disadvantage against the Mopar Hemi and Ford’s big FEs, and the Mark IV big-block first appeared on ’65 model year vehicles. The Mark IV big-blocks kept the 409’s 4.84-inch bore spacing but otherwise it went with a more conventional 90-degree deck and combustion chambers in the cylinder heads.
These days the aftermarket still offers a ton of support for both the first-generation small-block and the Mark IV big-block. But support for the W-series 409 is a lot more sparse. That was the challenge engine builder Keith Dorton, owner of Automotive Specialists, faced when a customer wanted a modernized 409 for his ’63 Impala restomod build.
Because of the unconventional combustion chamber design, the pistons by necessity must have a large dome. These forgings are from Ross Racing Pistons. That dome is 0.297 inches high and takes up 66.5 cc’s, which forces the rings way down. It also makes the piston heavy at 771 grams, but given the engine design there’s not much to be done about it.
So Dorton put together a recipe for a big-inch, completely modern 409 utilizing absolutely zero OEM components. That means port fuel injection, all-aluminum components, and one seriously sexy intake manifold.
For the build, the car owner and Dorton were able to source an aftermarket 409 block from Bill Mitchell Products and updated cylinder heads from Edelbrock, but there simply was no intake manifold available to fit his needs. So, they worked with Hogan’s Racing Manifolds to come up with a billet unit that’s an absolute jaw-dropper.
Like the crankshaft, the H-beam connecting rods are also from Molnar. They have a big-block-sized 0.990-inch wristpin.
Thankfully, it all came together to run just as great as it looks. This is going into a show car that’s going to get driven. But the owner is looking for good street performance and isn’t planning to take his expensive ride to the dragstrip. So, the cam choice is a bit on the small side for excellent torque right off the jump and good street manners. Still, 557 lb-ft of torque and 526 hp along with modern reliability ain’t nothing to sneeze at and should make this Impala scream like a scalded dog. We can’t wait to see it all come together!
An interesting feature of the 409 design is you actually don’t need a ring compressor to install the assembled pistons and rods into the block. Although the deck of the block is 74 degrees to the centerline of the crankshaft, the piston still travels perpendicular to the crank, making for an odd entry angle. That extra pocket that creates the combustion chamber is slightly larger than the actual cylinder bore, so the piston seems to slide in on an angle. If you are careful, the rings are compressed as the piston is pushed in by hand and a compressor isn’t necessary.Here, you can see the piston in the hole. The piston’s diameter is 4.500 inches and the piston top is flush with the deck (even though it is only a small portion of it). So with the 4.000 stroke that makes final displacement 509 ci.The cam is a hydraulic roller from Lamar Walden Automotive. The 409 uses the same 1-8-4-3-6-5-7-2 firing order as both Chevrolet’s small- and big-blocks, but this grind has a 4/7 swap, which has shown to be really helpful with big-inch engines. Otherwise, the lobes are ground with 244 and 253 degrees of duration at 0.050 tappet lift and 108 degrees of lobe separation.The cam is paired with a set of hydraulic roller lifters from Johnson. These have a tie-bar to keep the roller face in line with the cam’s tappets, so upgrading from the stock flat tappets is a piece of cake.To keep the oil from running right out the bottom of the engine Dorton is using a steel oil pan from Moroso with a 6.5-quart capacity. Large kickouts and a windage screen help control power-robbing windage.Like with the block, for the heads we’re going with new aluminum castings—except these are from Edelbrock. They are outfitted with 2.19-inch-diameter intake valves and 1.72 exhausts. You can also see how the intake and exhaust valves aren’t inline but offset. This arrangement is what gives the W-series engines their iconic valve cover shape.
Plenty of big 7/16-inch studs help hold the heads in place. The nut for each stud is torqued to 70 lb-ft with extreme pressure lube on the threads.The 1.540-inch-diameter springs are a dual-nested setup and can handle up to 0.600 lift. The retainers used are high-strength steel.Lamar Walden Automotive takes the already-healthy Edelbrock heads and both the intake and exhaust ports for improved flow.The BMP block moves the lifter bore locations, so getting a set of standard stud-mounted rocker arms to work can be difficult. Instead, Lamar Walden offers a set of aluminum rockers that are mounted on the pedestals you can see here. The tops are cut on a curve to keep the fulcrum properly aligned with the valvestem. To keep the stands from spinning, the manufacturer suggests drilling the heads and pinning the stands (you can see the holes in the stands). Instead, Dorton decided to mock up the proper rocker location and then weld a strap between the two stands so they cannot rotate. Also, you can see the shims to get the proper stand height for best valvetrain geometry. It’s a tricky setup, but it seems to work.Here, you can get a better look at the rockers in place. Notice that with the unique stands, no pushrod guides are necessary. But each rocker’s fulcrum bolts directly to the top of the stand, they must be shimmed properly to center the rocker over the valvestem tip.By the way, the valvesprings are set up with 140 pounds on the seat and 400 open. The aluminum rockers maintain the stock 1.7:1 ratio, so gross valve lift is 0.632 for the intakes and 0.636 for the exhausts.Up top we went way off the beaten path for the 409 with a full custom billet intake from Hogan’s Racing Manifolds. That’s one of Accufab’s high-flow throttle bodies bolted up front.Nothing new to add here, we just wanted another opportunity to show you all the gorgeous welding and machinework on the billet intake.
W-series engines are instantly identifiable by the unique scalloped valve covers. The stock ones were stamped steel. We’ve upgraded a bit here with these gorgeous castings from PML (which are all made in the USA). At this point, breathers still need to be added. You can see how they were cut and welded in place in the photo of the engine on the dyno.The front drive is all polished aluminum from Billet Specialties. A modern serpentine belt system should be much more efficient than the old-school V-belts the 409 was originally outfitted with.The distributor is a modern Dual Sync unit from MSD and required to work with the Holley Dominator ECU for the engine controls. It is made for a big-block, but Dorton made it work with the sleeve and spacer you see just above the valley cover.One hiccup we ran into was procuring a good set of headers for dyno testing. In short, we couldn’t get any. The stupid supply chain screwups bit us here. All we could get for the dyno test were these shorty headers that were a poor design and too small (just 1.75-inch primaries) for this engine, which surely hurt power production. The car builder is having some custom headers made, but they were still months out as this went into publication, and we just couldn’t wait.All engine controls will be handled by a Holley Dominator ECU, including timing and fuel control. Here, Jeff Dorton makes subtle changes to the fuel map while tuning on the dyno.Here’s the setup on the dyno. The final product? The big-inch 409 made 557 lb-ft of torque and 526 hp, but just like all W-series engines, it struggles to provide enough air in the upper rpm ranges and power fell off sharply after 5,500 rpm.
