Last month we set about building a big-inch big-block. Not big as in 496 or even 540 inches, but more like 582 power-making cubes. In addition to making power based on pure displacement, we also wanted this big-block to rev well into the upper 6,000-rpm range without falling on its face. To make it even more challenging we added the caveats that it had to run on 91-octane, have a hydraulic valvetrain, decent street manners, and enough vacuum to run power brakes.
In part one of the build we machined up a Dart Big-M block (4.600 bore) over at JR Competition Engines and filled it with a 4.375-inch forged Scat crank, Mahle pistons, COMP bumpstick (275/279 duration with 0.680-inch lift and a 112 LSA), and a rock-solid Moroso oiling system.
With the short-block complete, it was time to address the top of the engine. This is an area where you can spend a little or a lot of cash. Going budget will still make decent power, but if you want a big payoff you need to realize that sometimes you do actually get what you pay for. Bargain heads will make basement power, and stud-mounted rockers will work, to a point. But if you want to churn out the maximum potential power, and spin at a higher-rpm level, then parts from the upper shelves are required. Then again, you don’t want to go and buy the most expensive parts you can find under the misguided assumption that you’ll make even more power. The key here is to shop smart and get the “right” parts suitable for attaining your power goals and holding up to how you plan on running your engine. Spend too little and you’ll leave performance on the table, spend too much and you’ll have nothing extra to show for the lighter wallet. Do it just right and you’ll end up with a rock-solid mill that’ll bring a smile to your face every time you romp on the go pedal.
|Dart Big-M block
|Scat 4.375-inch stroke forged crank
|COMP hydraulic camshaft
|Scat H-beam rods
|Mahle forged custom pistons
|Mr. Gasket oil filter adapter
|COMP double-roller chain and gearset
|COMP billet aluminum cover
|ATI Super Damper
|Moroso high-volume pump
|Moroso 6-quart pan
|Fel-Pro gasket set
|ARP accessory bolt kit
|Big flow Dart CNC Pro1 355
|(Flow numbers at 28-inch water)
|Dart 355 CNC heads
|Dart aluminum valve covers
|Fel-Pro head gaskets
|Dart 4500 intake
|Fel-Pro intake gasket kit
|T&D Sport Comp shaft rockers
|COMP short-travel lifters
|COMP push rods
|COMP push rods
|MSD Pro-Billet distributor
|MSD billet hold down
|ARP head studs
|ARP assembly bolt kit
|Holley Ultra HP Dominator
Wire a set of bargain-basement speakers to your high-end stereo system and the result will be bad sound and tears. Well, cylinder heads are the same way. The best short-block money will be handicapped by poorly flowing, or improperly sized, heads. For this reason we went with these Dart Pro1 355 CNC aluminum heads (PN 19574136). They are specifically designed for big-inch, high-rpm use and every intake port, exhaust runner, valve bowl, and combustion chamber is 100 percent CNC-machined for optimal flow. This is done on a five-axis machine that can produce compound curves and complex shapes beyond what can be done by hand with a grinder. The assembled heads included a massive 2.300-inch intake and 1.880-inch exhaust stainless valves in addition to springs good for up to 0.790 lift and titanium retainers.
The Dart heads feature a chamber volume of 121 cc, which gave us an effective compression ratio of 10.6:1, which is perfect for premium pump gas. The exhaust ports are also 0.300-inch higher. To mate the heads to the block we used a set of ARP head studs (PN 235-4303) and a pair of Fel-Pro PermaTorque MLS head gaskets (PN 1077-1).
Most big-blocks don’t perform well at higher rpm levels due to lackluster valvetrains. Sure, stud-mounted rockers can be had from $300 to $600, but they just can’t hang at high rpm. As Brad Rounds, of T&D machine products, told us, “Shaft-mount rockers don’t make horsepower in and of themselves, but they allow you to make more power by providing a stable, high-rpm valvetrain platform to work from. For the absolute ultimate in horsepower and high-rpm stability, shaft roller rockers are a must. In addition to reducing flex, they also offer greater options in offsetting the rocker arms for different head and valve configurations.” Shaft rocker systems are known to cost a little more, but T&D recently released a new Sport Comp system targeted toward those on a tighter budget. By streamlining the manufacturing techniques, and removing options like internal oiling (not needed at these power levels) they were able to get the price down into an area that’s more wallet friendly. This T&D kit (PN 10010) included intake and exhaust ratios of 1.70 and priced out right over a grand.
For our application T&D supplied two different height stands. The taller (PN 00553 +125) was for the intake sides, while the shorter (PN 00550) was for the exhaust side. T&D was able to get the cost down on these rocker kits by limiting the number of ratios and offsets available as well as using less expensive retention hardware. They also left the bases bare and didn’t black oxide coat them. By removing features not needed for these power levels and applications T&D was able to get the cost down. The best news is that these rockers still utilize the same design and materials for bearings, shafts, adjusters, and rocker arms as in their premium systems.
To run these Sport Comp shaft rockers from T&D, dowel holes need to be drilled into the Dart cylinder heads. To make this simple T&D included a drill guide and detailed instructions. The other tool is a stand height gauge that’s used to determine which shims are needed to nail down the perfect geometry.
And here’s our Dart 355 heads with the dowel holes all properly drilled. It took a little effort, and careful reading and rereading of the instructions, but our reward will be a rock-solid valvetrain capable of higher rpm power.
With the locating dowel pins installed, we could use the supplied shims to get the proper rocker stand height. This shim height was found by using the included stand height gauge and following the T&D instruction sheet.
With the shims in place, we bolted down the intake and exhaust rocker stands, making sure to match up the intake and exhaust stands properly.
And here’s the T&D Sport Comp shaft rocker system completely installed. For our application we ended up needing eight COMP Hi-Tech chromoly heat-treated 3/8-inch diameter 7.550-inch (PN 8901-8) and eight at 8.680 inches in length (PN 7951-8).
If you want to rev a big-block higher, and not have to use solid lifters, then the best route is to go with something like these new black oxide–coated COMP short travel hydraulic roller lifters (PN 15854-16). Typical hydraulic lifters inevitably “pump up” at high rpm, which results in improper piston position and power loss. The short travel design limits the lifter’s internal piston and cuts down on the loss of power at higher rpm.
A 582 big-block wants air, lots of air, so we went with this Dart single-plane 4500 intake (PN 41124000). This design has a raised water crossover to insulate incoming air and the runner cross-sections help maintain high mixture velocity. They also have integral nitrous bosses if you want to go that route. Before installing, JR Competition Engines port matched the intake to our Dart 355 heads. The intake was secured using stainless six-point fasteners from our ARP accessory bolt kit (PN 535-9601) and a set of Fel-Pro gaskets (PN 1275).
Just like the valvetrain, the ignition system needs to remain stable at higher rpm levels. This MSD Pro-Billet distributor (PN 85551) incorporates two sealed ball bearings to maintain shaft accuracy to well over 10,000 rpm. There’s also a high-output magnetic pickup bolted to the base to accurately trigger the ignition. To hold it in place we also grabbed an MSD billet aluminum hold-down clamp (PN 8110).
Westech’s Steve Brulé helped us spec out the valvetrain and assembled the top end, including making sure the T&D rockers were correctly installed and adjusted. His other job was dialing in the Holley Dominator carb and making the whole deal sing on the dyno.
OK, so the polished Dart intake and valve covers made the engine look killer, but the real question was how it would perform on the SuperFlow 902 engine dyno. For gas we were running 91-octane pump gas.
We don’t know what sounds like more fun, 700 lb-ft of torque at 4,500 rpm (peak of 736 at 5,100 rpm) or 804 hp at 6,400 rpm. What we did notice was how stable the valvetrain remained throughout the pull. Even at 6,700 rpm, horsepower was just under 800 ponies and there were zero signs of valve float or other issues.