Hooker 2 1⁄8-inch primary...
Hooker 2 1⁄8-inch primary headers were used for our baseline runs. This size proved to work well for the 426 displacement Hemi, even in a high-output configuration. After a half day of tuning and tweaking, we cranked a full 494 hp and 499 lb-ft of torque from this combination-not bad at all.
We spent a half day on the dyno with the essentially stock Hemi, and then off it came for additional mods. With the factory combo, we already witnessed enough power to satisfy the needs of almost any power-hungry speed junky. Consider the entire package: mild compression for pump gas, a maintenance-free hydraulic cam spec'd for daily use, and a no-hassle single four-barrel carb sitting on a modest two-plane intake-about as foolproof as a combo can get. We had to wonder: If the Hemi could show these numbers in such a demure package, what would we find if we turned up the heat a bit?
Rollin' Thunder
Turning up the heat pointed us to the camshaft as a starting point, and this time we didn't fool around. We considered a Hemi a solid base for a serious performance mill, and we decided to move straight from a hydraulic flat tappet to a stout solid roller. Solid rollers aren't cheap, but neither are Hemis, so we felt justified. Instead of a full-on race roller, we opted for one of Crane Cams' street roller grinds-a PowerMax SR-254/374-2S-12. This cam is not for the fainthearted, spec'ing out with .254/.262 degrees duration at .050, and .587/.568-inch lift on the intake and exhaust lobes, respectively.
Along with the camshaft, the roller conversion requires the matching roller lifters, PN 66515-16, matching pushrods, PN 66624-16, and a camshaft thrust button, PN 99163, to keep the cam from walking in the bore. Also required with a billet roller is a compatible aluminum-bronze distributor drive gear, which we picked up from Milodon. A roller cam is much more aggressive than a hydraulic flat tappet, and requires a significant upgrade in valvesprings. We swapped out the factory single springs for a matched set of Crane duals (consult the cam manufacturer for recommendations for your application).
With the baseline in, we tore...
With the baseline in, we tore into the just-broken-in Hemi for a cam change. The crate comes with a hydraulic stick spec'ing out at .278 degrees of gross duration, and .495/.480-inch lift.
We then had a solid street-roller-equipped crate Hemi that was otherwise stock. We suspected some additional changes would be required to make the most of the new camshaft combination, but, at the time, we were content to run the engine with this single change and test it to see what kind of gain it would net. We had a bit of a delay before we could schedule a follow-up day on the Westech dyno. Unfortunately, the 950hp Holley carb we had used for a baseline was no longer available, so we substituted a 975 Race Demon carb on top of the factory dual-plane intake.
The Hemi cranked to life with the sound to match its serious performance looks. The stout street roller had the unmistakable burble of a heavy-hitting performance combo, but it wasn't so outrageous that we were afraid to run it on the street. Again, working the tuning loops, we zeroed in on the optimal jetting, and using the same 33-degree timing setting as in our previous test, we found 534 hp at 6,400 rpm. The cam change was worth 40 hp-a solid gain-and came with a good 700-rpm increase in usable powerband without detracting from power production lower in the rev range. Still, we felt the camshaft/cylinder-head combination should make some explosive power even higher in the rpm band. The key, we believed, would be to complement the combination with a change in the induction system to let it breathe even higher up the range.
With our new combo, the dual-plane factory intake manifold appeared out of place. We wanted a serious single-plane intake manifold that would add to the high-rpm breathing capacity of the Hemi heads worked by the Crane roller cam. To fill that bill, we scored a high-rise Barton single four-barrel manifold. The Barton piece has the unmistakable look of an intake single-mindedly designed for performance, and comes with Dominator-pattern carb-mounting provision. A Dominator or King Demon carb bolts directly in place, while a 4150 standard-pattern carb requires an adapter. We opted to move to a large-bolt-pattern carb-a 995 King Demon.
We weren't shy in selecting...
We weren't shy in selecting the replacement cam, moving to a Crane solid roller setup with a gross rated duration of .304/.312 degrees, .254/.262 degrees at .050, and .587/.568-inch lift at the valves. Lobe separation was 112 degrees.
The matching Crane solid-roller...
The matching Crane solid-roller followers went next, after being soaked in oil. The lifters slipped into place with no mods, even with the pronounced lifter bosses cast into the new Hemi blocks.
Crane also provided the roller...
Crane also provided the roller timing set and aluminum thrust button. Flat tappets provide a rearward thrust due to the cam's taper, while a roller cam does not. To prevent cam walk, a thrust button is needed.
We went back to the dyno and...
We went back to the dyno and changed the valvesprings, using compressed air in the cylinders to hold the valves up and a Landy tool to compress the springs for removal.
Westech's Steve Brule set...
Westech's Steve Brule set the lash to the recommended .020 inch on both the intake and exhaust valves. After running the engine and letting things settle, the lash was set again.
In the time between our last...
In the time between our last dyno session and our return with the cam change, one of our buddies at Car Craft Magazine made off with our test 950hp Holley carb (leave it to a boy with a bow tie). Luckily, we had a similarly sized Demon 975 hp on hand to provide the mix.