By Richard Holdener
Diehard Dodge guys might argue the fact, but the modern Hemi and (GM’s) LS have at least one important design criteria in common. Chevy guys will note that engineers stepped way up in the head flow department when they designed the LS family, especially the later (rec-port) LS3 motors. Not to be out done, the Dodge boys blessed their beasts with not only a ton of technology (Multiple Displacement Systems (MDS), Variable Camshaft Timing (VCT) or Active Intake systems, but impressive head gear as well. Like GM, the Hemi motors combine mild cam timing with impressive head flow to produce amazing power. Toss in the fact that only one manufacturer can claim ownership to the legendary Hemi name-and you start to see why the Dodge boys would rather fight than switch.
The head flow offered by the modern Hemi motors is important as it all but dictates how well the motor responds to other performance modifications, most notably cam timing. Right from the factory, the Hemi motors (5.7L, 6.1L and 6.4L) were blessed with impressive cylinder heads. In stock trim, the intake ports on the 5.7L heads top 260 cfm. That is enough airflow to support over 525 hp on a modified (normally aspirated) Hemi application. The larger 6.1L (and 6.4L) heads flow even more, but the icing on the cake is that all heads will respond to porting. We’ve seen ported Hemi heads post flow numbers topping 370 cfm. Why all the talk about head flow on a cam test? Since the Hemi motor already offered adequate displacement, compression and head flow, all it needed was more aggressive cam timing to show some serious gains. Basically you have a motor that has everything BUT a performance cam. When you add the right cam to a Hemi, you end up looking like a hero.
We recognized that the power gains would be greater on a 6.1L or 6.4L, but we decided to run this test on the more common (and now affordable) 5.7L Hemi. Before swapping cams, we had to select a suitable test motor. The after market is full of various crate and performance Hemis, but we decided to go the low-buck route and snag one from a local wrecking yard. Hemis were available in a variety of different applications, but our 5.7L test motor came from the engine bay of a 2006 Dodge Ram truck.
Like GM, Dodge trucks handily out sold their Hemi-powered performance cars, so look for a truck motor when searching for a project power plant. As delivered from the salvage yard, our 5.7L Hemi test motor came complete with wiring harness, sensors and full accessories (essentially a complete take-out motor) for $1,700. Compared to the popular 5.3L LS truck motor most commonly used by GM enthusiasts, the 5.7L Hemi offered both increased displacement and power. Let’s not forget the 5.7L was also sporting one of the most famous names in the industry!
Before running the Hemi on the dyno and performing a cam swap, we replaced the factory valve springs with 26918 springs from the COMP Cams catalog and filled the crankcase with Lucas 5W-30 synthetic oil. The motor was tuned using a FAST XFI management system and run through a set of STR8 exhaust manifolds. Run in otherwise stock trim, the 5.7L Hemi produced 385 hp at 5,500 rpm and 421 lb-ft of torque at 4,300 rpm. Illustrating that the Hemis know how to produce more than just peak horsepower was the fact that torque production from the 5.7L exceeded 375 lb-ft from 3,300 rpm to 5,300 rpm.
Though COMP offered a number of milder grinds for the Hemi, we stepped up to the XFI 273H-14. A healthy grind to be sure, the hydraulic roller cam offered a .547/.550 lift split, a 224/228-degree duration split and 114-degree lsa. We plan on installing ported heads at a later date and wanted a cam to work with our future upgrades. Equipped with the 273 cam, the 5.7L Hemi produced 449 hp coming at 6,100 rpm and 443 lb-ft of torque at 4,500 rpm. The cam swap increased the peak power output from 383 hp to 448 hp, a gain of 65 hp, but out at 6,300 rpm, the Hemi Helper offered an additional 100 hp!
Power Numbers: Stock vs COMP 273H-13 Cam
Run in stock trim with the spring upgrade and SRT8 exhaust manifolds, the stock Hemi produced 385 hp and 421 lb-ft of torque. That the Hemi produced more torque than horsepower was a sure indication of the mild cam timing, especially given the impressive head flow. Hardly a race cam, the 273H-13 offered impressive power gains. Swapping the cam netted an increase of 65 horsepower (peak to peak) and an additional 100 horsepower at 6,300 rpm. For stock motors looking for a sizable torque gains while maintaining idle quality, check out the smaller 260H-13 cam, but we plan on stepping up to ported heads and even a stroker short block, so we opted for the more aggressive 273H-13.