400ci Dart Aluminum Small Block Engine Build - Aluma-Mouse
This All-Aluminum Small-Block Demonstrates That Light Makes Might
From the April, 2010 issue of Chevy High Performance
By Bill McGuire
Photography by Bill McGuire
All-aluminum small-blocks have mystique. Even today, when production V-8s come with aluminum blocks straight from the showroom, there is still something magical about an all-alloy Gen I Mouse motor. Back in the '60s they were the acme of high technology, the signifiers of high-level factory connections, generally found only in exotic racers like Jim Hall's Chaparrals and Mickey Thompson's Indy cars. Here in the 21st century, aluminum small-blocks, now available to one and all straight off the rack, continue to dominate in venues where good power and light weight are key-sprint cars, to name one example.
All this is exactly what famed Detroit race car fabricator Ron Fournier was thinking when he went shopping for a new engine for his personal, handbuilt track roadster. Fournier designed his 1,600-pound bomb as a tribute to the great track roadsters of the '50s, and also as a sort of street-legal sprint car-he likes to hot-lap the roadster at local dirt tracks when he gets the chance. An all-aluminum small-block was the perfect choice for his rod, so he called his buddies at Dart Machinery in nearby Troy, Michigan, leading purveyors of aluminum Chevy blocks. The build for Fournier's engine was performed in-house at Dart's engine shop by Jeff Lake and Tony McAfee, the company's Pro Stock specialists.
Though the piece is cast in aluminum rather than iron, the Dart block bears some dimensional similarities to the Chevy-based Olds Rocket block originally marketed by GM Performance Parts. So while the Dart casting is somewhat non-standard compared to a conventional SBC, parts channels are still comfortably wide. To accommodate big stroker cranks, the oil pain rails have been spread outboard 0.400-inch on each side, while the camshaft is raised 0.391-inch in the block, rolling on big-block Chevy journals. Thus configured, the casting can accept bores of up to 4.185 inches and strokes of up to 4.125 inches, for as much as 454 ci. While Dart's block is most typically used in oval racing, the casting was designed from the start to support street hardware, including a mechanical fuel pump, a conventional distributor, and a wet-sump oil system. There are a few wrinkles involved in setting up the Dart block for road use, however, and we'll cover them here.
Pistons are Mahle forgings...
Pistons are Mahle forgings with an all-over Grafal coating, running conventional 1.5mm top and second rings with a 3mm, three-piece oil ring package.
Fournier's roadster may be a dirt sprinter in spirit, but for the engine buildup Lake and McAfee deliberately went 180 degrees from the typical high-revving, no-flywheel, light-switch combination employed in the circle-track world. Instead, they opted for real-world street performance, with good driveability and a big, fat torque curve. Sidestepping the more expensive and exotic reciprocating components, they set the displacement at 400 ci with a 4.125-inch bore and a 3.75-inch stroke. Since that's still on the biggish side for a small-block, their cylinder head choice for this engine may raise an eyebrow or two in some quarters: the Pro1 Platinum series with 180cc intake ports, the smallest offered by Dart.
Among his other duties at Dart, McAfee heads the company's advanced wet-flow bench research program, where he has developed some firm convictions about what works and what doesn't for a given combination. "This is the smallest port we offer and I would say it's way underestimated," he says. "The 180 has the best overall performance for the street and it's absolutely ideal for hydraulic roller cams. For power peaks below around 6,400 rpm and displacements up to 400 inches, this is the head you want." To finish off the conservative, high-velocity airflow combination, a 650-cfm Demon carburetor and a dual-plane Dart intake manifold were selected.
Dart's aluminum block comes...
Dart's aluminum block comes standard with screw-in core plugs and four-bolt, steel billet main caps at a street price of around $5,200. For the extremely weight-conscious, aluminum main caps are available at extra cost.
Engine Pro supplied the forged...
Engine Pro supplied the forged steel H-beam rods with 2.100-inch-diameter big ends, 6.00-inch center-to-center length, and floating pins.
The Pro1 Platinum series heads...
The Pro1 Platinum series heads selected for this engine feature 180cc intake runners for good all-around street performance. The heads are available bare or assembled with valves, springs, and guideplates.
Our buildup was performed...
Our buildup was performed by Dart's resident Pro Stock experts, Jeff Lake (left) and Tony McAfee.
Here's the correct way to...
Here's the correct way to apply RTV sealant-neatly, sparingly, and inboard of the fastener bores. The 0.400-inch spread pan rails require a non-standard pan gasket, PN Z1256 in the Fel-Pro catalog. The crank is an off-the-rack Eagle forging with 400-sized stroke and 350-sized main and rod journals.
Intake valves are 2.02-inch...
Intake valves are 2.02-inch paired with 1.60-inch exhausts. The crescent-shaped, 72cc chamber design was informed by Dart's wet-flow bench research, as is the five-angle valve job that comes standard on all Dart heads.