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.
As we mentioned, Dart's prediction for our project engine was 668 hp and-drum roll, please-that's exactly what we got: a peak of 668 hp at 6,000 rpm (668.9 horses, to be more precise). And while the dead-on prognostication was impressive, even more so was the overall performance of our big-bore 509. With its strong low-end torque and deep-breathing heads, the engine quickly started making big power. It crossed the 400hp level by 3,600 rpm and hit 500 by only 4,400 rpm. By 5,100 rpm it was making 600 hp and it kept pulling to nearly 6,500 rpm-that's some serious revs for a big-block street/strip engine and one of the primary reasons we were interested in exploring the big-bore/short-stroke combination.
Maskin, who's had decades of experience building racing engines, was philosophical about the results. Or, to put it another way, he wasn't surprised.
"We've been doing this a long time," he says. "We know what other engines of larger and smaller displacements make with the same basic components, so estimating the horsepower pretty much comes down to the displacement of the combination."
His confidence was reassuring and we were enthused to find our project engine exceeded expectations on all fronts. We already have an idea of what we're going to do with the engine, but that's another story for a future issue.