426 Crate Hemi Dyno Test

Lucky us! We happened to get our paws on a crate Hemi-and the green light to run it to within an inch of its life on the dyno. Even better, we had a chance to bolt on a selection of go-fast goodies to see how much easy power could be netted from the same basic package. Actually, our Hemi is a 426-cube crate engine from Mopar Performance, the smallest in their stable of Hemi crates.

The 426 Hemi crate is basically a turnkey engine, requiring little more than a carb and headers to run. The engines are fairly mild in specs but are rated at 465 hp-a fistful more than the original 426's 425hp rating. Like the original engines, the crate carries cross-bolted main caps and iron Hemi heads, and features a 4.25-inch bore combined with a 3.75-inch stroke. The camshaft is a hydraulic lifter profile with .278 degrees of duration and .495/.480-inch lift, while the valves are the traditional 2.25/1.94 package. Compression ratio is a pump-gas-friendly 9:1.

Bridging the gap between those mighty valve covers is a dual-plane, single four-barrel intake manifold, a departure from the original dual fours of legend. Mopar Performance also offers a longer stroke version of the crate Hemi, at 472 cubes with 525 hp, as well as an aluminum-headed 528ci version rated at a whopping 610 hp.

Hemis are known for one thing above all else, and that is making power. The free-flowing Hemi heads encourage airflow and allow for prestigious power production, even in stock form. While other engine designs need major cylinder-head upgrades to support high horsepower levels, the Hemi responds to high-performance mods with significant output gains while maintaining the basic engine package. Well, that's the theory we wanted to put to the test.

Our plan was simple: Open the box on the stock crate Hemi, add a carb and headers, and spend a day tuning on the dyno to see what kind of power we could extract. From there, we'd make a couple of specification changes via a hot-cam combination, as well as an upgrade in the induction and exhaust systems to see what could be accomplished.

Dyno Time: Baseline
Once the lid was cracked on the Hemi's shipping box, we added a complete Milodon dual external-pickup oil-pump package and full-length oil pan, since that configuration will be used when the engine is installed in a car. Next, the factory dual-plane intake manifold was topped with a vacuum-secondary 950-cfm Holley carb, and the Hemi was ceremoniously loaded onto the Westech Dyno.

Once the Hemi was loaded, a set of Hooker 211/48-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.