Hemi Horsepower Helper: 100 Horsepower Cam Swap

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.

We wish they were as cheap as LS motors, but this 06 5.7L Hemi take out set us back $1,700. Many of the components including the accessory drive were removed prior to the cam test.

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!

We wish they were as cheap as LS motors, but this 06 5.7L Hemi take out set us back $1,700. Many of the components including the accessory drive were removed prior to the cam test.

Long-tube headers would be ideal, but we did the next best thing by ditching the factory truck manifolds in favor of a set of SRT8 manifolds.

 

After running the stock cam to establish a baseline, off came the valve covers to provide access to the rocker shafts.

Many 5.7L Hemis (like ours) came equipped with MDS lifters. These applications must run the MDS solenoids. The non MDS motors can use the simple plastic plugs.

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.

After the baseline runs, off came the factory damper using an LS damper removal tool.

Next came the front cover to allow access to the timing chain, gears and oil pump. We made sure to remove the plugs and rotate the motor to TDC prior to removal of the timing chain.

The timing chain was secured using a single retaining bolt. We removed the bolt and set aside the timing chain. We liked the fact that there was no need to drop the pan or oil pump to facilitate the cam swap. The cam retaining plate was secured by three bolts. The third retaining bolt (not visible) was located directly behind the oil pump (still accessible from above).

Out came the mild stock cam and in went the healthy 273H-13 grind from COMP Cams. Like the GM LS, it was not necessary to remove the lifters to facilitate the cam swap. We just rotated the cam and pushed the lifters up into their respective lifter trays.

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!

Our stock 5.7L heads had been previously upgraded with 26918 Beehive springs from COMP Cams, so they were ready for the new cam profile. We also upgraded the pushrods during the cam swap.

Power Numbers: Stock vs COMP 273H-13 Cam

Stock COMP 273H-13
RPM HP TQ HP TQ
3000 210 368 212 371
3300 240 382 248 394
3600 275 400 283 413
3900 305 411 319 429
4200 335 419 353 442
4500 358 417 380 443
4800 375 410 401 439
5100 382 393 412 424
5400 383 372 423 411
5700 377 347 440 405
6000 364 319 447 391
6300 344 287 444 370

After installation of the COMP 273H-13 cam, the power output of our 5.7L Hemi jumped up from 385 hp and 421 lb-ft of torque to 449 hp at 6,100 rpm and 443 lb-ft of torque at 4,500 rpm.

Power Numbers

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.

Sources

COMP Cams
compcams.com

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Power & Performance News is the source for news, tech and products that help you get more performance from your vehicle. If powertrain performance projects and hardcore technical content are your interest, Power & Performance News is the publication designed for you. Our acclaimed editorial staff covers all aspects of engine and driveline upgrades with a mission of presenting information that is both interesting and achievable for the “average car guy”.
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