Last month, we introduced you to our Real Fine 509 Dart big-block buildup. It involved eschewing the conventional wisdom that the way to large displacement performance derives from a long stroke. Instead, we teamed with Dart Machinery to validate the theory that a larger bore and a conventional stroke length was the recipe for outstanding dual-purpose power.
Our target sounded simple enough: Build a 500-plus cube Rat of at least 600 hp that would be suitable for the street and strip. Dart answered with a 4.500-inch-bore/4.000-inch-stroke combination that delivered 509 ci. Basing his estimate on similar, yet smaller-displacement, combinations, Dart founder Richard Maskin predicted our project engine would make 668 hp.
In the previous installment, we followed the assembly of the short-block. With this segment, we finish off the engine and evaluate its dyno performance. In other words, we're going to see how close Dart is to its self-proclaimed bulls eye. Check out www.superchevy.com for a video of the engine on the dyno.
But first, an overview of the short-block: It consists of Dart's Big M iron cylinder block, an Eagle 4340-forged steel crankshaft, Engine Pro H-beam forged rods and JE forged aluminum pistons. The Big M block has a true priority-main oiling system, four-bolt billet steel main caps and, for our engine, a conventional 9.800-inch deck height (10.200-inch and 9.400-inch deck heights are available). As mentioned above, it uses 4.500-inch bores (4.600-inch-bore versions are available, too), which is considerably larger than a production, Mark IV-type big-block casting could handle. Indeed, a typical 454-style block with standard 4.250-inch bores can be safely overbored to 0.100-0.125-inch, yielding displacements of 476 and 481 ci, respectively, when used with a conventional 4.000-inch stroke.
So, we've got a big-inch short-block with an all-forged, heavy-duty rotating assembly. To that, Dart's builders added more Dart parts, including high-flow aluminum cylinder heads and a spider-type, open-plenum intake manifold, along with a Comp Cams hydraulic roller camshaft, with 0.540/0.560-inch lift and 242/248 duration specs, and complementing valvetrain. It's topped off with a Demon 850cfm four-barrel carburetor.
It's an amazingly simple combination that relies on no exotic parts, expensive machining or racer secrets. In a nutshell, X+Y=Z, only in our project, our X (the short-block) and Y (the heads/induction system) are really big. In fact, the large volume of the heads, along with a correspondingly-sized intake manifold and camshaft profile, go a long way to maintain robust torque in the engine. Compared with options only a few years ago, larger-volume heads and intakes, with long, straight runners, promote exceptional torque, even with a shorter crankshaft stroke.
Despite sticking with a conventional stroke length, we weren't too concerned about our project engine making strong torque-and neither was Dart's president, Richard Maskin.
"Torque is something you don't have to worry about with a 509-inch big-block, even with a 4.000-inch stroke," says Maskin. "Sure, you could get more with a longer stroke, but the combination we've laid out here will make more than 600 lb-ft across most of the power band. There's more than enough for any street/strip car."
Those thoughts were confirmed when we viewed the engine's performance on Dart's dynamometer. Right off the bat, it was generating more than 500 lb-ft. In fact, it registered 523 lb-ft at only 2,600 rpm and rose to 600 lb-ft by 3,800 rpm. The torque curve was broad and pretty flat between 2,900 rpm and 6,000 rpm, running between 580 at the low end of the tachometer, peaking at 623 lb-ft at 4,500 rpm and settling back to about 585 at 6,000. And with horsepower simply the product of torque multiplied by engine speed and divided by 5252 (TQ x RPM/5252), as long as the lb-ft readings stayed in that 600 lb-ft range as the revs climbed, achieving our 600hp goal would be a no-brainer.