426 Crate Hemi Dyno Test, 486 bhp Baseline! Options

[PBB]

426 Crate Hemi Dyno Test
Thrashing the Big Lung

By Steve Dulcich
Photography: Steve Dulcich

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.



There's something nice about being able to purchase a brand-new 426 Hemi in 2003, some 32 years after they originally went out of production. Credit Mopar Performance for keeping the Hemi alive and well. Add a carb and headers, and she's ready to run.

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.



We added a complete Milodon dual external-feed, swinging oil-pickup system and race pan, since this is the configuration it will run when installed in the car. Got oil?



The oiling system ensures an adequate oil supply under extreme dragstrip forces. It bolted on without a hitch.



We used a Holley 950hp vacuum secondary carb mounted on the stock MP dual-plane intake for our baseline testing.



An ATI Super Damper was bolted to the front of the crank in place of the OE piece to meet SFI safety specs when this baby hits the track.



We cheated a little with a Meziere electric water pump--a move that added to our power numbers by eliminating the parasitic drag of the stock belt-driven pump assembly. It saved considerable time, as it eliminated the need to set up a pulley system.

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.



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.

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?

ROLLIN' THUNDER



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.

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.



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.

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).



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 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 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 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.

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.



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.



With the roller cam, our fat-headed 426 Hemi was churning to the tune of 539 hp. We were pretty happy, but we knew there was plenty left without having to go back inside.

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.



It only stands to reason that a roller-cammed Hemi needs a serious induction. To fill that bill, we opted for a Barton high-rise single-plane. The Barton manifold is flanged for a large Dominator- base carb.

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.



Topping the Barton intake was a 995 King Demon carburetor. The combination of intake and carb gave our Hemi a look of pure power. We liked the look but wanted the numbers to back it up. We also changed out the stamped-steel valve covers for a set of cast MP pieces.

With the intake and carb change, our Hemi took on a different character, at least in the looks department. The wickedly sweeping divorced runners of the Barton intake and the fat King Demon carb had the look of serious hardware. While we found the appearance satisfying, we were more interested in the numbers. It seemed a shoe-in that the induction was the cork in our previous combo, and confidence was running high that the upgraded induction would let the rest of the combo swill some serious air and turn a number.

We found tuning the King Demon no more difficult than a conventionally sized carb, and we limited our tuning to running a standard jetting loop. The King Demon features replaceable air-bleed circuits; however, no changes were required to get a fine-looking fuel curve. With the induction change, we hit paydirt, recording 594 hp at 6,600 rpm within five dyno pulls. As is typical with a single-plane versus a dual-plane, the lower end of the torque curve softened some, but the high-end charge really woke up.

The intake and carb were worth another remarkable 60 hp, pushing the output of our 426-cube engine so close to the 600hp number we could taste it. We wanted to push the engine over the magic 600hp mark, but our dyno time was winding down. A little more flogging or a change to synthetic lube would have easily moved it over the hump.



The new combo put up the numbers when it came to the crunch, belting out a solid 594 hp at 6,600 rpm. What a difference an induction can make! We were within spitting distance of 600 hp, with a 9:1 426-cube motor through a pair of factory heads--but these are Hemi heads. We likely could have topped the 600 mark with a little tuning or by changing to a more slippery oil, but time was running short.

Stashed in the corner at Westech was a set of TTI 21/4-inch big-tube Hemi headers. On a 426-cube engine, we suspected they would be a little too much, but at least we gave them a try. Time was short, so we left our oh-so-close-to-600hp previous combo and made the move to the fat-tube headers. Unfortunately, they were a little too much for our combo, and we saw power drop over most of the range, with the exception of a blip above our previous output line in the midrange. It was clear we weren't going to hit our magic number with this combo, but, sorry pal, we were way past the two-minute warning, and there was no time to go back. Too much header cost us torque, power, and time.



We used the twilight of our dyno time to try a set of big-tube TTI headers with 21/4-inch primaries. They were too much for our little 426-cube mill, and the numbers showed it. Had we run them on a blown, nitrous'd, or big-cube engine like a 528 Hemi, the story would have been different.

So, how do we sum up this little adventure? Well, we can say what Mopar fans have known for years--Hemis make power. We had close to 600 hp on hand, close enough to call it there. When you consider we got there with only 426 cubes and the stock cylinder heads, it walks the walk. Try writing a list of other production engines that will do the same, and you won't have to worry about running out of ink.

- Mopar Muscle

[PBB]

What I find amazing is that while this engine hass 9:1 compression, puts out 486 horsepower and is completely streetable, there was a high power version of the original that had 12.5:1 compression, put out 550 horsepower and idled at 1500 rpms.
Straight from the factory!

[Peabody]

Wow....thats one powerful engine

[fallon]

drool drool drool


so how much do one of these badboys cost?

[PBB]

$12,000+

[fallon]

well i guess ou get what you pay for