The Chevy 409 has earned a rightful place in high-performance history thanks to its early success in Super Stock drag racing--and a certain pop song by the Beach Boys. But with a relatively brief production run that lasted from 1961 through 1965 in cars and 1962 through 1966 in trucks, perhaps only 100,000 409s were produced. Finding a good one today is next to impossible, and if you do, you'll need to wrestle it away from the restoration crowd.
Few enthusiasts realize there's a budget-friendly alternative to a scarce 409. We're talking about the comparatively unloved 348. Introduced in 1958 as the first member of Chevy's big-block engine family, hundreds of thousands were installed in passenger cars between 1958 and 1961, plus a bunch more in heavy-duty 1-ton Chevy trucks right up through 1966. Most experts agree that 348 production outpaced 409 production 5-to-1, so there are still plenty to choose from. We see 'em at swap meets all the time.
No, the 348 never inspired a hit pop song, but thanks to renewed interest from the aftermarket, you can transform a 348 into a 434-cube monster with enough power to rival any similarly built small- or big-block. The key ingredients are Edelbrock's new Performer RPM 409 aluminum heads, an Eagle stroker crank and H-beam rods, Ross pistons, an Isky solid roller cam, and a new single-plane four-barrel intake manifold from Lamar Walden.
Roll it all together with quality machine work, and you're looking at well over 500 hp at 6,200 rpm and 500 lb-ft at 5,500 rpm. The upshot is that we have a potent new engine family to play with, and can you imagine the shocked look on people's faces when you pop the hood on your Camaro, Chevelle, or Nova and they see one of these?
Let's watch as Joe Jill and the crew at Superior Automotive prepare and assemble the stroked short-block. Next month we'll complete the buildup and run it on the dyno.
What We Did
Transform a forgotten 348ci into a stroker 434ci
Its a potent package!
Before delving into the assembly,...
Before delving into the assembly, a quick look at the W's unique chamberless cylinder head configuration is required to better understand the unconventional engine block. Its decks are not milled at the usual 90 degrees; rather, they're cut at a 74-degree angle so the heads are tilted to form a wedge-shaped combustion chamber inside each cylinder bore.
Because of the tilted deck...
Because of the tilted deck surfaces, traditional deck height measurement techniques are not viable. Instead, Superior mounts the block on a Rottler F-67A CNC mill and uses a digital indicator probe to plot the actual 9.600-inch deck height. The crescent-shaped region above the counterbore forms the in-block combustion chamber.
Our 348ci to 434ci recipe...
Our 348ci to 434ci recipe starts by boring the stock 4.125 bores 0.030 over to 4.155 inches. Though sonic checking is a smart move prior to any cutting, these blocks are known to be plenty thick. Our bore walls measure a super-safe 0.175 average thickness after boring. A second operation enlarges the crescent-shaped combustion chambers atop each bore by 0.060 to a final size of 4.215. Chevy originally specified the oversize region to allow piston ring installation, and it's just as important today.
Billet steel main caps from...
Billet steel main caps from CRV 409 Parts are added to the center three positions and boost bottom-end reliability to 700 hp. Each cap is used as a drill fixture to accurately position the splayed outer bolt holes in the main webs. ARP 1/2-inch center studs and 7/16-inch outer bolts replace the stock 1/2-inch bolts.
The key ingredient in the...
The key ingredient in the stroker assembly is this forged 4340 steel Eagle crank. Its 4-inch stroke is 0.750 greater than the stock 348's 3.25 stroke. Since 348 blocks have more compact crankcase dimensions than 409 blocks, Eagle reduced the counterweight diameter so it drops right into the 348 block with room to spare. The drilled output flange works with manual and automatic transmissions.
The extra 3/4 inch of stroke...
The extra 3/4 inch of stroke creates block contact. Jill says he also encounters this when stroking vintage 396 and 427 blocks and already has the Rottler CNC machine station programmed to solve it. Since the W shares the same 4.48-inch bore spacing and major internal crankcase dimensions with the '65-and-up Chevy Mk IV big-block, the same clearance relief cutting program works fine on the W block.