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.
Dart's cylinder head studs...
Dart's cylinder head studs employ this bull-nosed profile designed to bottom out in the fastener bore, producing the proper light interference fit on the block threads as the stud is tightened.
According to Lake and McAfee, no special dimensional tolerances are required when assembling the aluminum block. Main and rod clearances were set a touch on the fat side, in the 0.003-inch range, but that's their preferred oil clearance for all their buildups, especially when they don't know how the engine will be broken in. No special goops or procedures are employed for head sealing, either; just quality studs and a standard Fel-Pro gasket with aerosol gasket adhesive. Really, there is only one arguably trick component in the entire engine: the camshaft. Because the Dart block's cam journals are big-block Chevy in diameter, the cam is a custom-order piece.
Comp Cams supplied the stick, a hydraulic roller grind, on its 12-000-9 core. Lobe lift is 0.363-inch on the intake and 0.361-inch on the exhaust, while intake and exhaust duration at 0.050-inch lift are 236 and 242 degrees, respectively. Lobe separation angle is 110 degrees and the cam was installed on the 108 degree intake centerline. With Dart 1.6:1 rocker arms, net lift works out to 0.581-inch on the intake and 0.577-inch on the exhaust. So while the lightweight block requires a non-catalog camshaft, the cam timing used here is fairly conventional small-block fare.
Due to the wider pan rails, an OE-style oil pan won't fit. But not to worry; pans are readily available off the shelf from Moroso and others, in both wet- and dry-sump varieties. If you've opted for a wet-sump setup with a standard Chevy oil pump like this engine, you'll need to use a big-block oil pump shaft to compensate for the elevated camshaft centerline. A remote oil filter is also required since the block lacks a filter pad. And if you're running a block-mounted mechanical fuel pump, you'll need a 0.200-inch-longer fuel pump shaft, available from Dart. Finally, you'll need to machine a 0.391-inch spacer to slip between the intake manifold and distributor-again, to adjust for the increased cam height-or you can simply use one of the many adjustable-sleeve distributors on the market.
With a Fel-Pro 0.041-in. head...
With a Fel-Pro 0.041-in. head gasket, the compression ratio works out to 10.02:1-compatible with 87-octane pump fuel.
Once assembled, the aluminum small-block went straight onto Dart's Stuska-Depac engine dyno to test the results. There, the small-port combination did not disappoint: From 6,000-6,500 rpm the mouse did better than 500 hp, with a peak of 528 hp at 6,100 rpm. And perhaps even more impressive, there's more than 400 lb-ft of torque available throughout the engine's rpm range, from 2,000 rpm on up, with peak torque, 512 lb-ft, arriving at 4,800 rpm. This lightweight small-block is a little torque monster. And all this was achieved with a hydraulic roller cam, a single four-barrel carb, and 87-octane pump gas. Now there's real street performance you can use every day. Of course, there's another bottom line where this build is concerned. Here's the question everyone is dying to know: What does the aluminum small-block weigh? To establish a baseline for comparison, first we weighed a late-model, all-iron small-block in the standard Dart dyno configuration: complete, less flywheel, water pump, and alternator. Thus equipped, the cast-iron mouse tipped the scales at 476 pounds. Then we moved the heavy-metal lump aside and tossed the aluminum mill on the scale. In identical dress, the Dart aluminum V-8 weighed only 366 pounds. Light weight, solid driveability, and proven small-block performance make for a hard combination to beat.
What is it
400ci build with a Dart aluminum block
It's a reliable package that looks impressive under any hood
When OE-style hydraulic rollers...
When OE-style hydraulic rollers are not an option, the Dart guys like to use Comp Cams or Howard's lifters in their house buildups. These +0.300-inch long pieces from Comp require 6.900-inch pushrods in the high-cam Dart block.
Rocker arms are Dart house...
Rocker arms are Dart house label pieces (not yet in the catalog) with a 1.6:1 ratio. Valvesprings are 1.437 inch in diameter, the standard components on the Pro1 assembled head.
An all-aluminum Mouse motor...
An all-aluminum Mouse motor begins to take shape in Dart's engine assembly room. The cast-aluminum timing cover with integral timing pointer and the 7-inch SFI crank damper are by Engine Pro.
A Dart dual-plane intake manifold,...
A Dart dual-plane intake manifold, Demon 650-cfm carburetor, and MSD Pro-Billet distributor complete the combination. Secondary ignition wires are MSD as well.
With a standard distributor...
With a standard distributor housing a 0.391-inch spacer is required, or you can use a distributor that employs an adjustable sleeve to compensate for the Dart block's elevated cam centerline.
The best numbers on the dyno...
The best numbers on the dyno were achieved with out-of-the-box jetting on the Demon carb and 37 degrees of spark advance, all in by 2,500 rpm.
|*Corrected to 60 degrees F, 29.35 inches Hg
|ALUMA-MOUSE COMPLETE PARTS LIST
|Aluminum race series block, 4.125-inch bore, 9.025-inch deck height
|Aluminum Pro1 Platinum cylinder heads, 180cc intake runners, 72cc chambers, assembled with valves, springs, retainers, seals, guideplates
|Aluminum intake manifold, dual-plane air-gap style, single carb
|Private label aluminum roller rocker arms, 1.6:1 ratio
||call for application
|Chrome stamped-steel valve covers
|Custom-ground cam on 12-000-9 core, big-block journals
||call for application
|Pro Magnum 0.300-inch tall Retro Roller lifters
|Pushrods, 5/16x7.100-inch, 0.080-inch wall
||call for application
|8.5mm plug wire set
|Crankshaft, 4340 forged steel, 3.75 stroke, 2.100-inch journals
|TM-77 main bearing set, standard
|Double roller timing chain and sprocket set
|H-beam connecting rods, 4340 steel, 6.0-inch
|Timing cover with pointer, aluminum
|7-inch SFI crankshaft damper
|Forged pistons, 4.125-inch bore, Grafal coating, with rings
|Oil pump, standard
|Oil pump driveshaft; big-block Chevy
|7-quart oil pan, 8.25-inch sump with scraper
|Carburetor, 650-cfm, mechanical secondaries
|Head gaskets, 0.041-inch compressed thickness
|Two-piece rear main seal
||call for application
|Timing cover seal and gasket set
|Oil pan gasket set