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.
There's something nice about being able to purchase a brand-new 426 Hemiin 2003, some 32 y
We added a complete Milodon dual external-feed, swinging oil-pickupsystem and race pan, si
The oiling system ensures an adequate oil supply under extreme dragstripforces. It bolted
We used a Holley 950hp vacuum secondary carb mounted on the stock MPdual-plane intake for
An ATI Super Damper was bolted to the front of the crank in place of theOE piece to meet S
We cheated a little with a Meziere electric water pump--a move that addedto our power numb