As crate engines go, GM Performance Parts' 454 H.O. crate engine is not only a bargain at its street price of around $4,600, its forged crank, pistons, and rods also make it capable of handling nearly as much power as you're capable of throwing at it. We proved that in our Aug. '03 issue ("Import Killer: 780 hp From 7.4L") by taking a bone-stock 454 H.O., swapping its stock hydraulic-roller cam for a bigger Crane Cams hydraulic roller, upgrading the GM dual-plane intake manifold to an Edelbrock Victor Jr. single-plane, and bolting on a Vortech carbureted supercharger kit for a total gain of more than 300 hp over the 470hp baseline.
It's not like there's anything wrong with the 454 H.O. as shipped. It's just that as with most things performance related, we're genetically incapable of leaving well enough alone, as evidenced by the fact that even 780 hp on pump gas was not enough. For a year, we've been waiting patiently for Air Flow Research (AFR) to release its newest big-block Chevy head: a 305cc intake-runner aluminum street head. Based on the performance we've seen from AFR's small-block Chevy and Ford heads, and combined with our experience using AFR's bigger race-oriented, CNC-ported big-block heads (see "911hp Big-Block Chevy," Aug. '03), we knew the as-cast 305cc street version would be the perfect choice for a pump-gas-friendly street/strip mill like the 454 H.O.
The 118cc combustion chambers in the stock rectangle-port cast-iron heads, combined with the small dome on the stock forged pistons, give the 454 H.O. a relatively low 8.75:1 static compression, which makes it a great candidate for supercharging. The 305cc heads have 119 cc chambers, so we had AFR mill our test heads slightly to reduce chamber volume to 112 cc's for a bump in compression to 9.2:1--still well-suited to the boost levels generated by the street-oriented Vortech supercharger kit we're using, but a bit snappier in a naturally aspirated combination. Our test heads also featured AFR's optional CNC-profiled chamber design, which greatly enhances the flow characteristics of the heads by unshrouding the valves. In fact, the set we tested was actually the very first set of 305s AFR produced with this new chamber design. As the accompanying flowbench results show (see sidebar), these heads really kick butt compared to the factory iron heads, especially on the exhaust side, and priced around $2,000 a pair fully assembled, they're quite affordable as aftermarket aluminum big-block Chevy heads go.
Operating under the bigger is better theory, in addition to the AFR heads, we selected a slightly larger Crane solid-roller cam to compare against the Crane hydraulic roller we tested in the previous configuration (see Cam Specs sidebar), had the Edelbrock dual- and single-plane intakes port-matched by AFR to their heads, stepped up to bigger 2-inch-primary headers, and then bolted the Vortech blower back on to see just how much power we could ultimately wring from an otherwise as-assembled 454 H.O. short-block.
When all the testing was done and the smoke had cleared from the dyno room, our final answer was an astounding 926 hp at 6,700 rpm and 756 lb-ft at 5,800 rpm. That's 2 hp per cubic inch on pump gas! When we ran our Import Killer headline last year, we got a bunch of letters from import guys calling us out for comparing a blown engine to some of the overhead-camshaft techno wonders that make the magic number of 100 hp per liter of displacement naturally aspirated. Well, we don't care how bad-ass some dude's naturally aspirated Honda S2000 motor is; if you go up against 900-plus pushrod ponies and 750 pounds of earth-shaking torque with a wrong-wheel-drive econobox, you're gonna get a fast and furious old-school ass-whipping.