In the Chevy world, very few engines have the wow factor of a 409. Be it a bone-stock restoration or a high-end race engine, the allure of a 409 lies in its unique design and rarity. When Chevrolet introduced the W-motor in 1958, it had a displacement of 348 ci and an odd appearance compared to the standard small-block Chevy, which had only been available for three years at that point. The 409 was introduced in 1961, and it was an evolution of the 348 design, utilizing a larger bore and a longer stroke.
The strange shape of the cylinder heads and valve covers makes these engines easy to spot, but there are lots of other differences that make the 348 and 409 unique. While it didn't take kindly to high rpm, it was a very popular engine combination in the 1960s. That's where our engine comes into play, as it once lived a tough life on the dragstrip. It was the motivation for a '55 Chevy drag car that ran in the Chattanooga, Tennessee, area in the mid-to-late '60s. The car was built and raced by Don Roberts of Graysville, Tennessee, but Don passed away a few years ago, so some of the details regarding the engine are fuzzy.
The casting number on the rear of the block (3830814) tells us the engine would normally be found in a '63 Impala. However, we noticed a peculiar detail as we continued to run the numbers. Like most Chevy blocks, the stamping pad is located on the front passenger-side of the engine. As we scraped away gunk and paint from the area, we couldn't find any numbers or letters—nothing. That told us this block had either been decked or it was an over-the-counter block. To get our answer, we rubbed muriatic acid over the stamping pad, as that can usually show the codes, even if the block has been decked. At this point, we still had not disassembled the short-block, so we did not have proper access to measure the deck height to double-check. After all of our theories and testing, we determined the block was an over-the-counter purchase.
As we continued to scrape around and find details on this engine, we filled the cylinders with oil and let them soak for a few days. Before starting the disassembly process, we wanted to turn over the engine, and we honestly did not know what to expect. We didn't know if it would be stuck due to a 30-year stint in a barn, but it required very little effort to get it spinning again. So far, so good.
Disassembly provided a couple of other strange details. The crankshaft casting numbers were barely visible, appearing to have been ground off, leaving only the last two numbers of the code: 72, which is the end of the 3788072 casting number. This designates a '61 crankshaft, which from our research, is no better or worse than any other 409 crankshaft. The high-performance 409 engines featured a windage tray, so the third and fourth main caps featured extra-long studs instead of bolts. These studs were in place but had been cut off flush with the main cap nut—an odd modification, but they obviously had some sort of reasoning behind it.
By far, one of the most peculiar aspects of this 409 was the assortment of parts that came with it. We have no way of confirming any of our speculation, but we can confirm that every single part that came with the engine was 348 equipment. Even the oil pan was a 348 piece, making our minds wander into the years of "it ain't cheatin' if you don't get caught" drag racing in the Southeast. Was this a cheater engine, claiming to be 348 ci, when it was really a 409? All signs point to yes.
The casting numbers would have given it away, but Don's '55 Chevy was allowed a 10 percent engine setback in the gas classification. That means the rear of the block would be tucked in tight against the firewall, making the numbers impossible to see. The block had no stamping codes, so the tech guy had no ammunition there. With 348 cylinder heads, intake manifold, and oil pan, this 409 could've been a wolf in sheep's clothing.
So if all this is true, why would a racer go to all this trouble to say he had a smaller engine? In the '60s, most classes were separated by the weight of the car and the (claimed) cubic inches. If you had a car with big cubic inches (such as a 409), you'd likely be forced to race in one of the faster classes such as A/Gas or B/Gas. However, if you had a smaller engine, like a 348, you could squeeze into a slower class, such as D/Gas and clean house, especially if that 348 turned out to be a 409.
Regardless of this engine's history as a drag racer, it proved to be quite resilient. As we disassembled the engine, we kept thinking, "There has to be a reason he took this engine out of the car." We expected to see at least one chewed-up journal or a scarred cylinder, but no, we found zero flaws in this barn-fresh 409 short-block. An unbelievable find, this 409 only needed a simple rebuild to be ready for action once again.
Follow along in this installment, as we reuse the original rotating assembly to preserve the history of a drag racer who is no longer with us. Despite some advice to have the block bored (regardless of the condition of the cylinders), we kept the original bore and will utilize the original 11:1 forged pistons. We know the heavy original pistons are not ideal for today's high-performance applications, but the fact that all of these parts were usable gave us enough reason to give up some horsepower.
Next month, we will finish the bottom end and update the barn-find 409 with Edelbrock aluminum cylinder heads and a Comp Cams hydraulic roller setup. Then, we'll end the three-part build with dual quads and a Pertronix ignition, which will be put to the test on the dyno. For now, follow along with the unearthing process and check out some of the features that make W-motors so unusual (and fun).
1 After removing the 348 oil pan, we were pleased to see the cleanliness of the rotating assembly, considering the lengthy dry spell. High-performance 409s had a windage tray, but the extra-long main studs were cut off to provide clearance for the 348 oil pan, which did not have enough room for the tray.
2 Light surface rust in the cylinders is usually a bad sign. We were optimistic and soaked the cylinders with oil before trying to spin the engine. Here, you can see the peculiar combustion chamber configuration, which is housed inside the cylinder instead of the head.
3 The casting number 3830814 means this is a block from 1963. All 409 engines from '63 used this block, including the Z-11 engine, which was actually 427 ci. The stamping numbers and suffix code on the front of the block generally determine the engine's configuration and horsepower rating.
4 The stamping pad on the front of the block should have given us an answer to this engine's original home, but it had no visible numbers or letters. That means this block was more than likely an over-the-counter piece from Chevrolet.
5 After spinning the engine over, we disassembled the rotating assembly to check for damage. Each and every component was in surprisingly good shape, including the crankshaft.
6 A closer look at the crankshaft casting numbers shows another odd modification to this engine's bottom end. For some reason, most of the casting number has been removed, leaving only the "72" on the end of the 3788072. This is a 1961 crankshaft.
7 We used emery cloth and sandpaper to clean the crankshaft's journals. We then used sandpaper to clean up the counterweights. The forged crankshaft checked out fine, so it will be reused.
8 The block was sent to Riverside Machine Shop to be cleaned and checked for cracks and distortion in the cylinders. It was determined that the cylinders did not need to be bored, so they were simply honed in preparation for the rebuild. Riverside also installed the new cam bearings and freeze plugs.
9 Years of neglect can cause major rust issues if the engine isn't stored properly. After we got the block back from Riverside Machine Shop, it looked like a brand-new casting. The lifter valley cleaned up nicely, and Riverside also ran a hone through the lifter bores.
10 One of the most unique aspects of 348 and 409 engines is the angle of the deck in relation to the angle of the cylinders. This wedge acts as the combustion chamber, meaning the cylinder heads are essentially flat on the mating surface.
11 Before we got too carried away with assembling the 409, we masked off the important stuff and laid down some classic Chevy Orange paint. High-temp engine enamel paint covers well and offers a glossy finish.
12 The flawless block is now ready for assembly. Before we can start installing the rotating assembly, we must take a few steps to help this engine survive some serious abuse.
13 Any time you're threading fasteners into an old block, it's a good idea to use a tap to clean out the boltholes. Since the bottom end was together when we found the 409, the boltholes for the main caps were in good shape. The cylinder head boltholes needed the most attention.
14 ARP main studs are threaded into the block and hand-tightened. ARP suggests hand-tightening the studs to ensure proper torque specifications when the nuts are installed.
15 Since the main journals were in great condition, we used standard bearings, opting for the Clevite brand. At this point, we installed the bearings into the block, making sure they were positioned correctly. Then we gave the bearings a healthy dose of heavy weight oil for lubrication.
16 Crankshaft installation is a two-man job. We lowered the crankshaft into place, making sure none of the bearings moved as we sat it into its final resting place.
17 The main caps can now be fit with new Clevite bearings. Heavy weight oil is used to coat the bearings. Also note the blue main seal and two small-black rubber end pieces. These are essential items, and they are included in all Fel-Pro 409 gasket sets.
18 After sliding all of the main caps into place, we gave the studs a coating of ARP Ultra-Torque fastener assembly lubricant. Old-school engine builders used regular motor oil for years, but Ultra-Torque lubricant ensures proper torque specifications.
19 We installed the ARP washers and nuts and then torqued them to 110 ft-lb in three equal steps. This torque specification is only accurate when Ultra-Torque lubricant is used, and keep in mind that these torque specs do not apply to original-style bolts.
20 All 409 engines came with a canister-style oil filter, so we used a Mr. Gasket kit to swap it to a more conventional spin-on filter. We used PN 1270, which calls for an AC PF-25 filter. That part number is discontinued, so we had the local parts store cross it out with a Wix brand, No. 51069.
21 The Mr. Gasket 1270 oil filter adapter uses the original bypass, which fits into the block with a rubber seal. Use red Loctite on the two adapter bolts and do not overtighten the bolts. Also pay close attention to the bellhousing bolt in this area, as the bolt can protrude into the aluminum housing and cause a nasty oil leak.
22 While the block is being prepared for final assembly, the pistons and connecting rods bathe in gasoline. This helps break down the carbon buildup on the pistons and ensures the ring grooves are free of any debris after a good cleaning with a wire brush.
23 After soaking and cleaning the pistons, the next step is installing the ARP rod bolts. We sent the rods to Riverside Machine Shop to have the new bolts pressed into place. After the bolts are pressed in, the rods are resized to ensure a perfectly round surface that matches the original journal size.
24 Tune in next month to see the 409 build continue by completing the rotating assembly, installing a pair of Edelbrock Performer RPM cylinder heads and a killer Comp Cams hydraulic roller setup.