5.7L Hemi Engine Build - Modern Mopar Muscle

XV conservatively rates the base engine package at 360 hp with the stock cam, but also offers upgraded packages, including more cam and the matching valvesprings, for ratings of 400 and 420 hp. The more powerful of these two packages, the XV Stage III, would be the subject of our next test. Featuring a COMP Cams camshaft with a rated advertised duration of 273/277 degrees, and measuring 224/228-degrees dura- tion at .050-inch tappet rise with .547/.550-inch lift, this is not a "wild" cam. Although considerably healthier than stock, the XV Stage III cam is moderate by conventional performance standards, especially in terms of duration. There was, however, the definite sound of performance, which was conspicuously absent with the OEM cam. To go along with the cam upgrade, the package also includes a set of uprated "beehive" valvesprings from COMP designed for the more aggressive valve action of the hotter stick. The ignition, carb, and intake setup remained the same, although the carb and spark calibration were changed to that offered for the Stage III package.

So what are a mild performance cam and the corresponding calibration worth in an otherwise all-stock 5.7 Hemi? As with the previous setup, the tuning was already done via the XV calibration, so all we needed to do was run for the numbers. Stout numbers they were, with peak horsepower now surging to 438 hp at 6,700 rpm, and peak torque recorded at 390 lb-ft at 5,200 rpm. The cam and spring change alone were worth a gain of 67 peak horsepower, and extended the useable rpm range by 900 rpm. We were impressed. Equally impressive was the fact that the added power did not come at the expense of torque, with peak torque increasing by a substantial 24 lb-ft. In fact, other than a slight loss in torque below 3,200 rpm, the larger camshaft got up and ran away from the output posted by the OEM cam combination. Unless you are building for a tow truck, there is little reason not to recommend the upgraded cam combination.

Swapping in Hemi power has never been easier with the components from XV, and one could argue that making Mopar power has never been cheaper or simpler. After all, we had a basically stock engine with a carb, intake, spring, and cam combo making a very streetable 438 hp. With the small-block of old, getting there would require head work, nasty levels of cam, or a combination of both. The new Hemi has unbelievable potential to offer for the streetbound Mopar. Unlocking that potential in a classic Mopar is as simple as turning the key with these parts from XV Motorsports. And the best part is that at the end of the day, you've got a Hemi to boot!

Finding A Hemi Core
Don't have a new Hemi lying around? All you need is a basic long-block like this one-you don't even need the computer, wiring harness, or even the fuel-injection manifold, for that matter. Even though they've only been produced since 2003, more than a million 5.7L Hemis have been turned out, so they're becoming more plentiful with each passing month. We had no problem finding them for sale on eBay and at core suppliers like Street & Performance (479-394-5711) for around $2,500.

Why does a nearstock new Hemi make so much power? The key is in the heads, with unobstructed ports leading to the opposed-valve layout. As the valves open, they are directed toward the bore'scenterline, eliminating the effects of bore shrouding. Note the Hemi's dual plug arrangement.