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Cammin' The Hemi -- Engine MastersPutting Comp's New Hemi Grinds To The Test From the February, 2009 issue of Popular Hot Rodding By Steve Dulcich
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Chrysler's new line of Hemi engines is a worthy successor to the legendary status of the Hemi of yore. Not convinced? If the stock performance of the new powerplant isn't enough to get your attention, get the wrenches out and you'll find the Mother Lode of easy power. We did, and judging by the numbers, the Hemi is in a league of its own in terms of small-block power. We've been on the dyno plenty with traditional small-block engine packages, and if the criteria is to make power from a production based engine, Chrysler's new Hemi reigns among the best. The stock power output just hints at the potential within. We had the opportunity to tap into some of that hidden potential, thanks to the new line of cams just off the grinders at COMP Cams. These are not radical Pro-Street race grinds, mind you, rather hotter grinds aimed squarely at street performance, with duration numbers ranging from a conservative 208-degrees, to a moderate 224-degrees; hardly the type of wicked 'shafts that will rattle your teeth. It didn't take a crystal ball to predict that the Hemi would be hungry for the extra lift and duration, what with its stingy factory cam specing out at meager 196-degrees duration at .050. What was shocking was just how much power and rpm was waiting to let go. We closed dangerously near the 500 hp and 7,000 rpm mark with the largest of these sticks. That the Hemi would belt out these kinds of numbers borders on the astounding, considering the modest 9.6:1 compression ratio and 346 cubes. There's power to be had with this Hemi engine, maybe more than you bargained for.  COMP Cams has recently introduced...  COMP Cams has recently introduced a new line of XFI hydraulic rollers for the new generation of Hemi. As luck would have it, we had a Mopar Performance 5.7 crate on the pump to see for ourselves what they were worth.  Mopar's crate engine is based...  Mopar's crate engine is based upon the truck 5.7 Hemi with some changes to make it suitable for retrofit application. The engine is available in either an MPI fuel injected version, such as our test engine, or equipped for a four-barrel carburetor. Mechanically, the engine assembly is straight production, with the exception of a unique cast aluminum intake manifold. The engines are shipped with production truck exhaust manifolds and cams.  A closer look at the Mopar...  A closer look at the Mopar Performance crate engine's intake manifold reveals a single-plane layout, with a centrally mounted throttle body, an induction aimed at making the engine more adaptable in retrofit applications. The four-barrel carbureted intake shares the same basic layout.  Baseline testing the crate...  Baseline testing the crate engine in totally stock form netted peak power numbers of 376 hp at 5,700 rpm, and 372 lb-ft of torque at 4,600 rpm, at STP correction factor. Not bad! We figured since we were going to run some hot cams through the engine, we'd first address the exhaust situation by ditching the factory log manifolds.  TTI makes these beautiful...  TTI makes these beautiful 1 3/4-inch full-length headers, designed to fit a new Hemi into a conventional A, B, or E body chassis. The headers were worth big dividends in power and torque, raising the bar to 393 hp at 5,700 rpm, and 390 lb-ft at 4,700 rpm. With this baseline of nearly 400 hp with the production cam still in place, we were ready to look for even more with the COMP cams.  One additional change was...  One additional change was required before we could run the cams, and that had to do with the engine management system. The Mopar Performance controller is not readily programmable for the serious modifications we had in mind. We needed full control over the fuel and spark curves, as well as a much higher rev limit to really get the most of our new cams. Westech's fuel injection guru Tom Habrzyk, wired the Hemi with components from FAST.  How do you change cams in...  How do you change cams in the new Hemi? Actually, it is one of the simpler engine designs to work with. Begin by removing the crank damper and timing case casting up front, and the valve covers up top.  The Hemi engine is far ahead...  The Hemi engine is far ahead of older engines in terms of gasket sealing, using captive O-rings or rubber gaskets to seal the major castings and valve covers, rather than the paper or cork gaskets of older engines. These can survive several cam changes without the need for replacement.  Under the valve covers, you'll...  Under the valve covers, you'll find two rows of shaft-mounted rockers, just as you'd expect in a Hemi engine. Unbolt the rockers, using the time-honored technique of backing the mounting bolts off a little at a time to avoid stressing the shafts, and remove the rockers and pushrods. Keep track of the position of the rocker assemblies so that they go back on in the same position.  otate the engine over to line...  otate the engine over to line up the timing marks of the cam and crank gears, then remove the cam drive gear. The sheetmetal wheel attached to the cam gear signals the cam position for the ECU.  Behind the cam gear is the...  Behind the cam gear is the tensioner assembly, which also serves as the thrust plate for the camshaft. It can be unbolted and removed to gain access to the cam. The timing chain is captive due to the front crankshaft-mounted oil pump, and can be just draped over to the side, out of the way.  There is no need to pull the...  There is no need to pull the intake manifold, or lifters with the Hemi engine. Just rotate the cam in the bore through several turns, and the lifters will be retained in the up position.  With the camshaft removed,...  With the camshaft removed, a view down the lifter bores reveals that the lifters are held up away from the lobes by the guide/retainers, much like with a GM LS-series engine.  With the factory cam out,...  With the factory cam out, the COMP replacement cam is carefully slid into position. We started with the smallest of COMP's offerings for the Hemi, the XFI 260 (see spec chart).  Reassemble the cam drive by...  Reassemble the cam drive by realigning the timing marks and bolting on the cam gear. The timing chain tensioner has a provision to be pinned back, relieving the chain tension to ease the installation. From here, it's just nuts and bolts to reassemble the engine and it's ready to run.  We were rewarded for our efforts...  We were rewarded for our efforts with substantial power gains, even with the smallest of the cams tested. We scored 424 lb-ft at 4,800, and 443 hp at 6,200 to 6,500 rpm. That's a gain of 50 hp and 34 lb-ft with the smallest of the COMP Cams.  Back in for round two, we...  Back in for round two, we opened the Hemi again to install the mid range cam, the COMP XFI 268. This cam proved to be a real sweet runner, making for a very nice balance of idle quality and all-out power. Power was up another 20 hp to rate at 463 hp, while torque output was little changed recording 423, but peaking at a higher 5,000 rpm.  Our Martini shot of the day...  Our Martini shot of the day came with the installation of the biggest of our trio of cams, the XFI 273. While it's the largest cam of the currently available series, it is relatively mild in specs by the standards of brawny street cams, measuring a comfortable 224/228-degrees duration at .050 inch. Power proved the potential lurking in the Hemi, recording a blistering 491hp peak at a jaw-dropping 6,900 rpm, while torque checked in at 417 lb-ft at 5,000 rpm. Does the new Hemi have muscle? With nearly 500 hp on tap from a stock engine with a street cam and headers - oh, yeah!
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