Once the Hemi was loaded, a set of Hooker 21/8-inch ceramic-coated headers were bolted to the heads, and the factory mechanical water pump was replaced by a Meziere electric unit. There's nothing quite like those gleaming valve covers to draw attention, and the Hemi got more than its fair share. With a flick of a switch on the dyno console, it fired to life, and it was showtime.
After several pulls on the dyno, the optimal jetting for our 950hp Holley was square at 82 jets front and back. We recorded a best of 486 hp at 5,800 rpm--a good 21 hp over the rated output. Considering the electric water pump, we figured the numbers were right on the mark. We set the ignition timing at 38 degrees total. Next, we ran through a timing loop, surprised to find the Hemi gaining power as timing was pulled out. With a setting of 33 degrees, we recorded a new peak output of 494 hp at 5,700 rpm. When you consider a displacement of only 426 cubes and near-500hp output with a relatively mild combo, it's hard to argue with the concept of Hemi power.
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?
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).
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.
Hooker 2-1/8-inch primary headers were used for our baseline runs. Thissize proved to work
With the baseline in, we tore into the just-broken-in Hemi for a camchange. The crate come
We weren't shy in selecting the replacement cam, moving to a Crane solidroller setup with
The matching Crane solid-roller followers went next, after being soakedin oil. The lifters
Crane also provided the roller timing set and aluminum thrust button.Flat tappets provide
We went back to the dyno and changed the valvesprings, using compressedair in the cylinder
Westech's Steve Brule set the lash to the recommended .020 inch on boththe intake and exha