Chevy Big Block Crate 454 Engine - Import Killer, Part 2

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.

The 454 H.O.'s factory-equipped hydraulic-roller camshaft requires a cam retainer plate to prevent the camshaft from "walking" back and forth in the block. Standard Mark IV roller-style camshafts won't interchange.

Flow Results

As you study these charts, notice how much more air the smaller AFR intake runner flows at every lift point compared to the factory head.

The intake-to-exhaust flow ratio of the AFR heads is also much better than the stock heads. For example, at 0.600-inch valve lift, the AFR exhaust ports flow about 77 percent of the intake, compared to 59 percent for the iron head. This means you might be better off using a single-pattern camshaft that opens the exhaust valves later in the combustion process, because the longer the exhaust valve stays closed, the longer time the combustion pressure has to push on the piston to make power.

The charts also reveal the gains in flow from the design of AFR's optional CNC-profiled chamber design, which unshrouds the valves and improves flow by maximizing the efficiency of the valve job and port-throat design, especially at lower valve lifts.

Finally, we've included the flow data AFR cylinder head designer Tony Mamo provided us after he port-matched the two Edelbrock intake manifolds we used in this test, a Performer RPM dual-plane and a Victor Jr. single-plane, and reflowed the 305cc head through each manifold. These are the airflow numbers the engine actually sees when it's running, and it reveals that regardless of how well any cylinder head flows, it's only as good as the manifold that's attached to it.

The Easiest 900 hp Ever

This little propeller inside the Vortech blower looks like it belongs in a kitchen blender, but it stuffs enough air into our big-block to provide scary power levels. We tagged 926 hp with only 6.9 psi of boost.

This little propeller inside the Vortech blower looks like it belongs in a kitchen blender

For the clincher, we brought back our secret weapon: a Vortech YS-trim centrifugal blower. We covered the installation and operation of this carbureted blow-through system in the original Import Killer article in Aug. '02, and we changed absolutely nothing when we bolted it back on for this go-round. The blower components were reinstalled onto our 454 in less time than it takes to change an intake manifold, and we didn't even change the jetting in the Mighty Demon carb installed inside the Vortech carburetor airbox. As a precaution against detonation, we filled the fuel system with Unocal 100-octane fuel, retarded the timing to 30 degrees before top dead center, and let it rip for the numbers.

The blower's boost level can be dialed in with a pulley ratio change. A smaller pulley on the blower spins it faster to generate more boost and undoubtedly more horses.

The blower's boost level can be dialed in with a pulley ratio change. A smaller pulley on

In typical centrifugal supercharger fashion, the higher the engine revs, the more boost is generated, carrying the torque curve with it. With torque comes horsepower, and it basically came down to a matter of at what rpm we wanted to draw the line and stop. We bumped the total timing to 32 degrees and set the dyno control to a peak of 6,800 rpm. The 454 rewarded us with 926 hp at 6,700 rpm with a humble 6.9 psi of boost. The implication is clear--with the Vortec-blown combination, output is limited only by our nerve and the remarkable strength of the 454's bottom end.

--Steve Dulcich

The "Partial" Crate Engine

By now, some of you may have noticed that not much is left of our 454 H.O. "crate engine" except for its original short-block. Also recognizing what an excellent foundation this short-block represents, GMPP now offers the 454 H.O. as a partial engine package (PN 12498778), which comes with a four-bolt block, a 1053 forged-steel crank, 4340 forged-steel rods, forged-aluminum pistons, a damper, a flexplate, a front cover, an oil pump, and an oil pan. Scoggin-Dickey Performance Parts lists it for $3,298 plus shipping.

Dyno Results