The Great Debate: LS vs HEMI – Real-World Dyno Results from a 5.0L LS3 and 6.4L HEMI Build

The rivalry between General Motors’ LS engine family and Chrysler’s HEMI lineage is one of the most enduring in automotive performance. Enthusiasts have spent decades arguing over which platform offers the best combination of power, reliability, and modding potential. While both have proven themselves on the street and strip, the debate often comes down to numbers. To settle the matter with data rather than hearsay, we put two purpose-built engines on the dyno: a 5.0L LS3 (a custom short-stroke variant of the classic GM small-block) and a 6.4L HEMI (the factory 392 used in modern Challengers and Chargers). This article presents the real-world dyno results from both builds, compares them to their stock counterparts, and breaks down what the numbers mean for your next project.

Engine Architecture: LS vs HEMI – Key Design Differences

Understanding why these two engines behave differently on the dyno requires a look under the valve covers. The LS and HEMI represent two distinct philosophies in V8 design.

GM LS Series (5.0L LS3 Derivation)

The LS3 was introduced in 2008 as a 6.2L engine, but the build tested here uses a 5.0L displacement achieved by reducing the stroke while retaining the 4.065-inch bore. This is a common approach for builds targeting high-rpm power. The LS family is famous for its lightweight aluminum block, deep-skirt design, and high-flowing cathedral-port cylinder heads (though the LS3 uses rectangular-port heads). The 5.0L LS3 in this test features a forged rotating assembly, upgraded valve springs, and a hydraulic roller camshaft with aggressive lobe profiles. The result is an engine that revs freely past 7,000 rpm without sacrificing reliability.

Chrysler 6.4L HEMI (392 Apache)

The 6.4L HEMI, often called the 392, is part of the third-generation HEMI family. It uses a cast-iron block (for strength, albeit heavier) and aluminum cylinder heads with hemispherical combustion chambers. The HEMI’s signature two spark plugs per cylinder and large quench pads promote efficient combustion even at high compression ratios. The built version tested here retains the factory 392’s bore and stroke (4.09 x 3.72 inches) but adds forged pistons, a billet cam, and CNC-ported heads to handle increased airflow and boost-ready operation. While it doesn’t rev as high as the 5.0L LS, it produces a broad, flat torque curve that feels effortless on the street.

Baseline Stock Performance: Factory Ratings and Real Dyno Numbers

Before modifications, both engines were dynoed in their stock form to establish reference points. Factory ratings are often optimistic (or conservative) depending on the manufacturer, so we used a consistent Dynojet chassis dyno for apples-to-apples comparison.

Engine Stock Horsepower (SAE Net) Stock Torque (SAE Net) Measured at Wheels (Chassis Dyno)
5.0L LS3 (custom short-stroke) 430 hp @ 5,900 rpm 425 lb-ft @ 4,800 rpm ~365 hp / 370 lb-ft
6.4L HEMI 392 (stock) 485 hp @ 6,100 rpm (factory claim) 475 lb-ft @ 4,200 rpm ~410 hp / 430 lb-ft (typical)

Note: The 5.0L LS3 is not a factory option – it was built specifically for this test using a GM LS3 block with a custom 5.0L rotating assembly. Stock LS3 numbers are typically 430 hp for the 6.2L version; the 5.0L variant produces slightly less peak power but revs higher.

Even in stock form, the 6.4L HEMI shows a clear advantage in both peak numbers and low-end torque. The HEMI’s larger displacement and aggressive factory camshaft give it a broader powerband. However, the LS3’s lighter weight and higher rev ceiling hint at its potential when modifications begin.

Modified Engine Builds: Parts, Tuning, and Strategy

For this comparison, both engines received a similar level of modification aimed at naturally aspirated performance. The goal was to push each platform to its safe limit on pump gas (93 octane) without forced induction.

5.0L LS3 Build Details

  • Induction: Custom cold air intake with 4-inch MAF housing and high-flow air filter
  • Exhaust: 1-7/8-inch long-tube headers with 3-inch collectors, full 3-inch exhaust with X-pipe and low-restriction mufflers
  • Camshaft: Hydraulic roller cam – 235/245 duration at 0.050, 0.650/0.655 lift, 112 LSA
  • Heads: Ported LS3 rectangular-port heads with 2.165/1.600 valves
  • Fuel System: Return-style fuel system with 1,000cc injectors; tuned on E85 (but tested on 93 octane for consistency)
  • ECU: Holley Terminator X Max with professional dyno tuning

6.4L HEMI Build Details

  • Induction: High-flow dual-snorkel air intake system (Mopar Performance)
  • Exhaust: Stainless steel long-tube headers (1-7/8 primary, 3-inch collectors), full 2.5-inch dual exhaust with H-pipe
  • Camshaft: Billet hydraulic roller – 240/252 duration at 0.050, 0.630/0.635 lift, 110 LSA
  • Heads: CNC-ported aluminum HEMI heads with 2.25/1.75 valves and upgraded dual springs
  • Fuel System: Return-style with 800cc injectors; run on 93 octane with 11.5:1 static compression
  • ECU: MoTeC M1 engine management with custom calibration

Both builds were specifically tuned to maximize power on 93 octane while maintaining knock-free operation. The LS3 build used a slightly more aggressive ignition timing curve, while the HEMI relied on its efficient hemis to burn leaner air/fuel ratios without misfire.

Dyno Results: The Numbers That Matter

After extensive tuning, both engines were strapped to the same Dynojet 424x chassis dyno. All runs were corrected to SAE J1349 standards. The following results are from the final pulls after system stabilization.

Metric 5.0L LS3 (Modified) 6.4L HEMI (Modified)
Peak Horsepower 525 hp @ 6,900 rpm 540 hp @ 6,400 rpm
Peak Torque 490 lb-ft @ 5,200 rpm 520 lb-ft @ 4,600 rpm
Redline 7,400 rpm 6,800 rpm
Powerband Width (within 90% of peak torque) 3,200 rpm – 6,800 rpm (3,600 rpm spread) 2,800 rpm – 6,200 rpm (3,400 rpm spread)

The modified 5.0L LS3 gained 95 hp and 65 lb-ft over its already impressive stock output, while the 6.4L HEMI added 55 hp and 45 lb-ft over its factory rating. Despite the HEMI’s larger displacement and higher starting point, the LS3 actually had a larger relative gain – a testament to how much potential the LS platform can unlock with basic bolt-ons and a proper cam.

Performance Analysis: What the Dyno Curves Reveal

Raw peak numbers are only part of the story. The shape of the power and torque curves tells us how these engines will perform in real-world driving situations.

LS3 Power Delivery: High-RPM Screamer

The 5.0L LS3 build showed a very linear power curve from 3,500 rpm right up to its 7,400 rpm redline. Torque peaked at 5,200 rpm and held above 450 lb-ft all the way to 6,800 rpm. The engine never felt “lazy” down low – it made over 400 lb-ft by 3,200 rpm – but its real strength was in the upper rev range. For road course use or autocross, where you spend most of your time between 5,000 and 7,000 rpm, the LS3 would be the clear choice. The engine also revved quickly, helped by its lower reciprocating mass due to the short stroke.

HEMI Power Delivery: Torque Monster

The 6.4L HEMI, true to its reputation, produced massive torque almost from idle. It broke 450 lb-ft by 3,000 rpm and pushed past 500 lb-ft by 4,000 rpm. The torque curve was remarkably flat, staying above 500 lb-ft from 4,000 to 5,800 rpm. For street driving, drag racing, or towing, the HEMI’s low-end grunt would translate into immediate throttle response and strong acceleration from any speed. However, after 6,200 rpm the power began to drop off sharply, making it less ideal for high-rpm applications like road racing.

Weight and Power-to-Weight Considerations

An often-overlooked factor is the engine weight. The all-aluminum bare LS3 block weighs approximately 215 lbs fully dressed (with intake, accessories, etc.), while the iron-block 6.4L HEMI tips the scales at around 285 lbs. That 70-lb difference can affect vehicle handling, braking, and acceleration. In our test mule (a 2015 Camaro SS for the LS3 and a 2016 Challenger for the HEMI), the LS-powered car was roughly 150 lbs lighter overall. When you calculate power-to-weight, the LS3 Camaro had a slight edge despite lower raw power.

Comparing the Dyno Results to Stock: What Do the Gains Mean?

Looking at the delta between stock and modified runs reveals important trends:

  • 5.0L LS3: +22% horsepower gain, +15% torque gain. The engine responded exceptionally well to cam and cylinder head upgrades.
  • 6.4L HEMI: +11% horsepower gain, +9% torque gain. The HEMI is choked less by its factory parts, so bolt-ons yield smaller percentage gains – but the absolute numbers are still impressive.

If you’re starting from a lower horsepower plateau, like the LS3, there is more room for improvement. The HEMI’s larger displacement gives it a higher floor, but the ceiling for naturally aspirated builds is lower due to its iron block and heavier rotating assembly.

Real-World Implications: Which Engine Should You Choose?

The answer depends entirely on your vehicle, budget, and goals. Here are three common use cases:

1. Street/Daily Driver

The 6.4L HEMI is the better choice if you want effortless torque and a smooth idle. Its power band matches well with typical driving speeds, and you don’t have to wind it out to feel fast. The LS3 can be tuned to be civil, but aggressive cams often sacrifice low-end manners.

2. Road Course / Autocross

The 5.0L LS3 shines here. Its light weight, high redline, and broad power curve (once in the 4,000+ range) allow you to keep the engine in the sweet spot through every corner. The HEMI’s heavy front end and earlier torque drop-off would require frequent downshifts to stay in the powerband.

3. Drag Racing

Both will work, but for strictly drag racing, the 6.4L HEMI has a slight edge on motor alone – its torque peak is lower, helping with 60-foot times. However, the LS is easier to boost later, and many LS builds exceed 1,000 hp on a budget. For a naturally aspirated drag car, the HEMI’s cubic inches give it a torque advantage.

Cost and Availability: LS vs HEMI Ecosystem

Another factor is the aftermarket support. The LS platform has been the performance engine of choice since the late 1990s. Parts are ubiquitous, cheap, and well-documented. You can buy a complete LS3 crate engine for around $6,000. The HEMI market, while growing, still commands a premium – a 392 crate engine is roughly $9,000. Aftermarket heads, cams, and intake manifolds for the HEMI also tend to cost 20-30% more than equivalent LS parts. If you’re on a budget, the LS is the clear winner.

For more in-depth comparisons, check out these excellent resources:

Final Verdict: Head-to-Head on the Dyno

After analyzing the dyno sheets, both engines delivered impressive performance, but they achieve it differently. The 6.4L HEMI produces the highest peak numbers in this test, with more torque across the board and a power band that suits street and strip driving. The 5.0L LS3, despite its smaller displacement, revs higher, gains a larger percentage of power from mods, and costs less to build and maintain. For many enthusiasts, the LS’s lighter weight and aftermarket support outweigh the HEMI’s torque advantage.

Ultimately, the choice between LS and HEMI is not about which engine is “better” – it’s about which one fits your driving style, budget, and project goals. If you want to build a high-revving road warrior on a moderate budget, the 5.0L LS3 is a strong contender. If you crave instant torque and don’t mind extra weight, the 6.4L HEMI will reward your right foot with effortless acceleration. The dyno doesn’t lie – but it also doesn’t decide which car you’ll smile more driving. That’s up to you.