Introduction: The LS vs. Hemi Rivalry

The debate between General Motors’ LS engine family and Chrysler’s Hemi has raged in garages and on forums for years. Both platforms are legendary for their ability to produce massive power, but they take very different paths to get there. The LS is celebrated for its lightweight architecture, affordable aftermarket parts, and high-revving capability. The Hemi, with its signature hemispherical combustion chambers, delivers brutal torque and a deep, iconic rumble.

When the goal is 700+ horsepower, both engines can deliver — but the required hardware, tuning strategy, and overall cost vary significantly. This article dives into the essential components for achieving 700+ HP on each platform, with a focus on forged internals and high-flow cylinder heads. We also explore forced induction, fuel system upgrades, and real-world build examples to help you decide which path fits your project.

Understanding LS and Hemi Engine Architectures

LS Engine DNA

GM’s LS family debuted in 1997 and quickly became a favorite among performance enthusiasts. Key traits include:

  • Lightweight aluminum blocks (most generations) that reduce front-end weight and improve handling.
  • Six-bolt main bearing caps for superior crank support under high loads.
  • Oiling system design that allows high-rpm operation without starvation.
  • Vast aftermarket support — heads, cams, intakes, and forced induction kits are widely available for nearly every budget.

The most common LS platforms for 700+ HP builds are the 6.2L LS3 (found in ’08+ Corvettes and Camaros) and the 7.0L LS7 (from the C6 Z06). Both respond exceptionally well to forged internals and high-flow heads.

Hemi Engine Heritage

Chrysler’s modern Hemi family (introduced in 2003) revived the legendary hemispherical combustion chamber design. These engines are known for:

  • Cast-iron or aluminum blocks depending on the generation — the earlier 5.7L and 6.1L were iron, while the 6.4L (392) and 6.2L Hellcat variants use aluminum.
  • Large-displacement potential — stock Hemis can be stroked to 426 cubic inches or more.
  • Strong bottom ends from the factory, especially the Hellcat’s forged crankshaft and rods.
  • Excellent torque curve — Hemis produce peak torque lower in the RPM range than most LS engines.

The 6.4L 392 Hemi is the most popular choice for 700+ HP naturally aspirated builds, while the 6.2L Hellcat Hemi is already capable of exceeding 700 HP with minimal modification.

Forged Internals: The Foundation for 700+ HP

Whether you choose an LS or a Hemi, pushing beyond 600 crank horsepower on stock internals is risky. Forged components are the only way to ensure reliability at high power levels — especially under forced induction.

Forged Pistons

Forged pistons resist thermal expansion and cracking far better than cast or hypereutectic pistons. Both LS and Hemi builds commonly use 2618 or 4032 alloy forgings from manufacturers like Diamond Pistons or JE Pistons. For 700+ HP, opt for a piston with a thick dome and a wrist pin designed for high boost.

Forged Connecting Rods

Stock powdered-metal rods will fail under sustained high power. Both platforms benefit from I-beam or H-beam forged rods made of 4340 steel. For LS engines, Carillo and Callies rods are common choices; for Hemis, K1 Technologies or Oliver rods are popular. A rod length of 6.125″ is typical for LS stroker builds, while Hemi builds often use 6.200″ or 6.350″ rods depending on stroke.

Forged Crankshafts

A forged crank handles the torsional loads of high-rpm and high-boost operation. LS cranks in 4.000″ stroke (stock LS7) or 4.125″ stroke (stroker) are common. Hemi cranks are often offset-ground to achieve larger displacement — a 4.250″ stroke with 6.350″ rods yields a 426 cubic inch Hemi, a classic combination.

High-Flow Cylinder Heads: The Key to Airflow

Factory cylinder heads restrict airflow on both LS and Hemi engines, especially once you add a larger camshaft or boost. High-flow heads allow the engine to breathe efficiently, making more power without increasing cylinder pressure dangerously.

LS Cylinder Head Options

For LS builds, the aftermarket is vast. Some of the best heads for 700+ HP include:

  • PRC (Precision Race Components) LS7-style heads with 260+ cc runners and 2.200″ intake valves.
  • Mast Motorsports LS3 heads with CNC porting and lightweight, high-lift springs.
  • AFR (Air Flow Research) 245cc or 260cc eliminator heads — proven for high-horsepower naturally aspirated and boosted applications.

Aim for flow numbers above 340 CFM at 0.600″ lift for a 700+ HP LS build. Porting the intake and exhaust manifold also helps maximize head flow.

Hemi Cylinder Head Options

Hemi heads have larger combustion chambers from the factory, but aftermarket options still offer significant gains:

  • Thitek CNC-ported heads for the 6.4L Hemi — flow over 370 CFM with proper valve sizing.
  • MMX (Modern Muscle Xtreme) stage 3 ported heads for Hellcat applications, featuring oversized Inconel exhaust valves.
  • BES Racing Engines full custom Hemi heads designed for 1,000+ HP.

For 700+ HP naturally aspirated, aim for at least 350 CFM intake flow. For forced induction, slightly more port volume is tolerable because boost pressure compensates for minor flow losses.

Forced Induction: The Fastest Path to 700+ HP

While naturally aspirated builds can hit 700+ HP on either platform, they require aggressive cams, high compression, and premium fuel. Forced induction (supercharging or turbocharging) makes the goal far easier to achieve.

LS Forced Induction

An LS3 or LS7 with forged internals and high-flow heads can easily exceed 800 HP with a modest supercharger kit. Popular options include:

  • ProCharger D-1X or F-1A-94 centri blowers — support up to 1,200 HP with proper intercooling.
  • Magnuson 2650 or 2300 roots-style superchargers — instant throttle response and huge low-end torque.
  • Twin turbo kits from Hellion or BorgWarner — great for road course cars due to better heat management.

With a forged LS short block and quality heads, 700 HP is achievable at 8–10 psi of boost on 93 octane pump gas. Run E85 and you can push 14–16 psi for 900+ HP.

Hemi Forced Induction

Hemi factory supercharger packages (Hellcat, Demon) already produce 707+ HP from the factory. Upgrading a Hellcat to 850+ HP is straightforward: pulley swap, injectors, tune, and a high-flow blower inlet. For naturally aspirated 6.4L Hemis, adding a Vortech or Kenne Bell supercharger with forged pistons and rods yields 750–850 HP reliably.

Turbocharging a Hemi is also common — the 6.2L and 6.4L blocks can handle 1,000+ HP with proper head studs and a billet main girdle. The downside is that aftermarket turbo kits for Hemis are generally more expensive than LS equivalents.

Fuel System and Tuning Considerations

700+ HP engines consume fuel at a shocking rate. Both platforms require upgraded fuel pumps, injectors, and management systems.

  • Fuel pumps: A triple-pump in-tank setup (like an Aeromotive Stealth system) or a brushless external pump works well for both LS and Hemi. For E85 compatibility, ensure all parts are ethanol-rated.
  • Injectors: 1,300 – 2,000 cc/min injectors (or 95 lb/hr and up for gasoline). Direct injection is available on later LT and Hemi engines, but for 700+ HP many builders convert to port injection for better compatibility with high-flow heads.
  • ECU tuning: LS builds benefit from Holley HP EFI, MoTeC, or stock ECU reflashes (HP Tuners, EFI Live). Hemi builds often use HP Tuners for Chrysler or aftermarket standalone ECUs from Haltech or MoTeC. A proper dyno tune is non-negotiable for reliability and safety.

Cost Comparison: LS vs. Hemi 700+ HP Builds

One of the biggest factors in deciding between LS and Hemi is budget. Below is a rough comparison for a 700+ HP street-driven build using forged internals and high-flow heads with a centrifugal supercharger.

Component LS Build Cost Hemi Build Cost
Short block (forged)$3,500–$5,500$5,000–$8,000
Cylinder heads (CNC ported)$1,800–$3,200$2,500–$4,200
Supercharger kit$4,000–$6,500$5,500–$9,000
Fuel system + tuning$2,000–$3,500$2,500–$4,500
Total approximate$11,300–$18,700$15,500–$25,700

LS builds are typically $4,000–$7,000 cheaper because of higher production volume and more competition among aftermarket manufacturers. However, Hemi builds offer a unique sound and torque curve that many enthusiasts consider worth the premium.

Reliability and Longevity

When built correctly, both LS and Hemi engines can last tens of thousands of miles at 700+ HP. However, a few factors affect long-term reliability:

  • Cooling: LS engines tend to run cooler due to aluminum construction, but Hemis (especially iron-block versions) hold more heat. Upgraded radiators and oil coolers are essential for both.
  • Oil starvation: At high RPM, Hemis are more prone to oil pooling in the heads because of the larger combustion chamber volume. A high-volume oil pump and baffled pan are recommended for Hemi builds. LS engines benefit from a trap-door oil pan mod.
  • Valvetrain wear: LS engines with high-lift camshafts need heavy-duty trunnions and springs; Hemis require careful lifter selection to avoid failures (Johnson 2110 lifters are popular for 6.4L builds).

LS in Modern Muscle and Swaps

The LS is the go-to engine for swapping into third- and fourth-gen F-Bodies, Fox-body Mustangs, early Novas, and even BMWs or Mazda RX-7s. In newer GM chassis, an LS3 or LS7 upgrade is straightforward. The LS’s compact dimensions and light weight make it ideal for track-focused builds.

Hemi in Dodge/Chrysler Platforms

Hemis are most commonly found in Challengers, Chargers, 300s, and Ram trucks. The Hellcat and Redeye platforms already offer 707–797 HP stock, making them a starting point for 1,000+ HP builds. Hemis are also swapped into classic Mopar A-bodies (Dart, Duster) owing to their period-correct appearance and monstrous torque.

Conclusion: Which Platform Should You Choose?

Both the LS and Hemi can hit 700+ horsepower with forged internals and high-flow cylinder heads. The right choice depends on your goals, budget, and the vehicle you’re building.

  • Choose an LS if you want a lighter engine, lower cost, and an immense selection of off-the-shelf parts. It’s ideal for track cars, road racers, and budget-conscious builds.
  • Choose a Hemi if you want massive low-end torque, that unmistakable Mopar sound, and the street cred of a legendary name. It’s perfect for drag strip warriors, muscle car purists, and high-horsepower street machines.

No matter which path you take, investing in quality forged internals and professionally ported cylinder heads is the foundation for a reliable 700+ HP engine. Combine those with a well-matched forced induction system, proper fuel delivery, and a skilled tune, and you’ll build a powerplant that dominates the road — and the dyno.

Looking for more detailed part recommendations? See the latest builds on EngineLabs and MotorTrend for hands-on advice.