Supporting Mods Breakdown: Camshafts, Intake Manifolds, Exhaust for LS vs HEMI Builds

Building a high-performance engine—whether it is a GM LS or a Chrysler HEMI—requires more than just a big cam or a set of headers. Success depends on how well the camshaft, intake manifold, and exhaust system work together as a system. Each component must be selected to complement the others and match the intended use of the vehicle. This breakdown will cover the key differences and best practices for LS and HEMI builds, helping you choose the right parts for your power goals.

If you are new to engine building, start by understanding that the camshaft controls when valves open and close, the intake manifold directs air into the cylinders, and the exhaust system removes spent gases. When these are properly matched, you gain maximum power, throttle response, and reliability. Mismatched parts can lead to lost performance or even engine damage. We will explore each component in depth and then discuss how to combine them effectively.

Camshafts: The Heart of the Build

The camshaft is often the first modification enthusiasts consider because it directly influences power band, idle character, and peak output. Both LS and HEMI engines respond well to aftermarket cams, but their architecture and aftermarket support differ significantly.

LS Camshafts

LS engines feature a pushrod design with a cam-in-block layout, which allows for compact packaging and relatively low cost upgrades. The aftermarket for LS cams is enormous, with options ranging from mild street grinds to aggressive competition profiles. Popular choices include the Texas Speed cam and the factory LS3 cam (often used as a baseline upgrade). Key things to consider:

  • Lobe separation angle (LSA): Tighter LSAs (110–112°) produce a choppy idle and shift the power band higher; wider LSAs (114–116°) idle smoother and maintain vacuum for accessories.
  • Valve lift and duration: LS heads flow well up to about 0.650" lift; exceeding that often requires upgraded springs, retainers, and pushrods.
  • Variable valve timing (VVT): Late-model LS engines (e.g., L99, LS3 with VVT) require VVT phaser limiters or specific VVT cams to retain timing control.

For a street-driven LS, a cam in the 220–230° duration range at 0.050" with 112–114° LSA works well with bolt-ons. For boosted builds, a wider LSA (115–118°) helps reduce overlap and prevent reversion.

HEMI Camshafts

HEMI engines (Gen III and Gen IV) use dual overhead cam (DOHC) or pushrod designs depending on the generation. The 5.7L and 6.4L HEMIs are pushrod engines, while the Hellcat and 6.2L stretched versions are also pushrod, but the architecture is different from LS. HEMI cams must account for the HEMI's unique combustion chamber shape and offset rocker geometry. Popular aftermarket cams include the Mopar Performance cam and grinds from Comp Cams.

  • Lobe separation: HEMIs generally respond well to LSAs around 112–114° for street/strip use; tighter LSAs can work but may cause vacuum issues in street cars.
  • Valve lift: Factory HEMI heads flow well to about 0.600" lift; beyond that, head porting and upgraded springs are recommended.
  • VVT and MDS: Many HEMIs come with Multi-Displacement System (cylinder deactivation) and variable cam timing. Deleting MDS requires a non-MDS cam and appropriate lifters, while VVT can be locked out with a phaser limiter or replaced with a fixed phaser.

For naturally aspirated HEMIs, a cam in the 230–240° duration range at 0.050" paired with a 112–114° LSA provides strong mid-range and top-end gains. For forced induction, a cam with less overlap (wider LSA) is advisable to reduce reversion.

Cam Selection Considerations for Both Platforms

  • Power band goals: Decide whether you want peak power at 6500 rpm or a broad torque curve from 3000 rpm.
  • Drivetrain compatibility: A very aggressive cam requires a higher stall converter for automatics or a no-lift shift tune for manuals.
  • Emissions compliance: If you need to pass a smog test, choose a cam with reasonable overlap and maintain catalytic converters.

Intake Manifolds: Fueling the Fire

The intake manifold must supply an even, dense air charge to all cylinders. A mismatch between cam and intake can rob you of power or create distribution issues. LS and HEMI manifolds differ in design and available upgrades.

LS Intake Manifolds

The LS platform offers a wide range of intake manifolds, from budget-friendly to race-ready. Factory LS3 and LS7 manifolds are excellent for mild builds up to 600–650 hp. For higher power levels, consider:

  • Holley Hi-Ram: A high-rise dual-plane style manifold that works well for forced induction or high-rpm naturally aspirated builds.
  • LSX (GM Performance): A large plenum manifold designed for 5.3L and 6.0L LS engines; it flows well and accepts standard LS fuel rails.
  • Fast intake: The LSXR manifold offers a CNC-machined runner and plenum for maximum airflow; it can support over 1000 hp.

When selecting an LS intake, match the runner length to your cam's power band. Shorter runners (e.g., Hi-Ram) favor high-rpm power, while longer runners (e.g., truck manifolds) improve low-end torque. A common mistake is installing a high-rpm intake on a mild street cam, resulting in soggy bottom-end response.

HEMI Intake Manifolds

Factory HEMI intakes (like those on 5.7L and 6.4L engines) are plastic with integrated runners and are adequate up to about 550–600 hp. For higher outputs, aftermarket options include:

  • Edelbrock Supercharger manifold: Designed for supercharged applications, this manifold improves airflow under boost and works with stock HEMI heads.
  • Mopar Performance intake: A cast aluminum manifold that flows significantly better than factory plastic units; it's a direct bolt-on for 6.4L HEMIs.
  • Bodied intake: Some builders use custom sheet metal intakes for extreme builds, but these require significant fabrication.

HEMI intakes often use a longer runner design than LS intakes, which helps torque but can limit top-end breathing. If you are swapping to a larger cam, consider porting the factory manifold or upgrading to a Mopar Performance unit. Keep in mind that HEMI cylinder heads have a unique port shape and spacing, so aftermarket intake compatibility is more limited than LS.

Intake Manifold Guidelines

  • Fuel system: Ensure the manifold works with your injectors and fuel rails. Most aftermarket LS intakes accept standard LS injectors, while HEMI intakes may require adapters.
  • Throttle body: A larger throttle body can be a bottleneck if the manifold is restrictive, but too large a throttle body can hurt throttle response on a relatively small cam.
  • Cold air intake: Pair your manifold with a high-quality cold air intake that supplies ambient air, not hot underhood air.

Exhaust Systems: Freeing the Flow

After drawing in air and burning fuel, the engine must expel exhaust efficiently. An exhaust system that is too restrictive will choke power, while one that is too large can reduce exhaust velocity and hurt low-end torque. Both LS and HEMI engines benefit from headers and a properly sized exhaust.

LS Exhaust Systems

Long-tube headers are the gold standard for LS performance. They scavenge exhaust pulses better than shorty headers, especially with a larger cam. Popular brands include Borla and Corsa. Key considerations:

  • Primary tube size: 1.75" primaries suit mild cams (up to 450 hp), 1.875" for 450–650 hp, and 2.0" for 650+ hp. Oversized primaries can lose low-end torque.
  • Collector size: A 3" collector is common; 3.5" collectors help on high-horsepower builds but are louder.
  • Catalytic converters: High-flow cats (e.g., Random Technology) flow well and keep the vehicle emissions legal. Some aftermarket cats are designed to handle high exhaust temperatures.
  • Cat-back systems: A 3" cat-back exhaust with a cross-pipe or H-pipe is typical for LS swaps. Straight-through mufflers (Borla Atak, Magnaflow) provide aggressive sound without excessive restriction.

For LS engines with a cammed idle, a 3" dual exhaust is common. If you are building a turbo LS, consider a 3.5" or 4" single exhaust to reduce backpressure.

HEMI Exhaust Systems

HEMI builds also benefit from headers, but the available options are fewer than for LS. Long-tube headers for 5.7L and 6.4L HEMIs are available from American Racing Headers, Kooks, and Mopar Performance. Key aspects:

  • Header type: Long-tube headers are preferred for maximum power, but shorty headers can be a simpler install and fit in factory engine bays without modifications.
  • Primary size: 1.75" to 1.875" primaries are typical for mild to moderate builds; 2.0" primaries fit high-horsepower setups.
  • Exhaust diameter: A 3" dual exhaust is recommended for most HEMI builds. Many aftermarket cat-back systems are designed specifically for HEMI-charged cars like Chargers and Challengers.
  • Sound profile: HEMI engines have a deep, rumbling tone. Exhaust systems with resonators reduce drone, while straight-through designs amplify the exhaust note.

HEMI engines with the factory active exhaust system (available on many modern Chargers) can be retained if you choose a system that supports the electronically controlled valves. This helps keep the exhaust quiet during cruise but opens up for wide-open throttle.

Exhaust System Considerations

  • Material: Stainless steel (304 or 409) resists corrosion better than aluminized steel; it is worth the extra cost for a daily driver.
  • Emissions: Some states have strict catalyst requirements. Aftermarket catted headers must be CARB-approved if you live in California.
  • Sound level: Aggressive cams combined with open exhaust can exceed track noise limits; consider adding resonator or performance muffler if you autocross.

Putting It All Together: Matching Cam, Intake, and Exhaust

Selecting each component in isolation will not yield the best results. The camshaft, intake manifold, and exhaust system must be chosen as a matched set to achieve your power goals. Here is how they interact:

  • Cam and intake: A long-duration cam that shifts the power band to higher rpm will benefit from a high-rise intake with short runners. Conversely, a mild street cam with low duration works best with a dual-plane or factory intake that favors low-end torque.
  • Cam and exhaust: More overlap from an aggressive cam requires an exhaust system with good scavenging qualities. A long-tube header with a 3" collector helps pull exhaust gas out, reducing reversion. For boosted applications, a less aggressive cam with a wider LSA pairs better with a free-flowing exhaust to prevent too much reversion under positive pressure.
  • Intake and exhaust: The intake and exhaust systems should be sized similarly. A high-flow intake without a matching exhaust creates a restriction on the exhaust side, limiting power. If you install a huge cam and big intake but retain stock exhaust manifolds, you will leave a lot of power on the table.

A common combination for a naturally aspirated LS street build is a 228/232 duration cam, LS3 intake manifold, and 1.875" long-tube headers with a 3" cat-back. For a comparable HEMI build, a 234/240 duration cam, Mopar Performance intake, and 1.875" long-tubes with a 3" dual exhaust yields similar gains. Always confirm that your engine management system can handle the cam's fueling needs—especially for VVT and MDS systems.

Conclusion: Making the Right Choices for Your LS or HEMI Build

Supporting mods—camshaft, intake manifold, and exhaust system—are not just a laundry list of parts. They are a system that must work in harmony. For LS engines, the aftermarket offers incredible breadth and depth, making it easy to find parts for any power level. HEMI engines enjoy a growing aftermarket, but require careful attention to platform-specific details like VVT, MDS, and cylinder head geometry.

When planning your build, start with a realistic power target and a driving goal. Then select a cam that moves the power band where you want it, an intake that breathes at that rpm range, and an exhaust that matches the flow demand. Use reputable manufacturers known for consistent quality, and verify compatibility with your engine controls. Whether you are building a street cruiser, a weekend track car, or a show-stopping drag racer, a well-matched combination of cam, intake, and exhaust will deliver the performance you are after while keeping the engine reliable and enjoyable to drive.