Battle of the Gen 5 LT Intake Manifolds: Holley Hi-Ram vs. CID

When it comes to squeezing every ounce of performance from your Camaro or Corvette Gen 5 LT, the intake manifold plays a pivotal role.

Enthusiasts and builders often debate the merits of different intake setups, and two names that frequently surface are the CID and the Holley Hi-Ram. Recently, we had the opportunity to test these two titans back-to-back on Brandon Hill’s new 454 Gen 5 LT1 Direct Injection (DI) hydraulic engine. The results were illuminating.

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The Test Setup

Before diving into the numbers, here’s a quick overview of our test setup:

• Engine: GPI 454 LT DI hydraulic engine with the following specifications:
  • Compression Ratio: 16:1
  • Displacement: 454 CI
  • Platform: Gen V LT
  • Heads: GPI 9k Heads
  • Camshaft: GPI Custom Cam
  • Pistons: Diamond Pistons
  • Crankshaft: Callies Magnum Crank
  • Air Intake: Bellmouth Velocity Stack Air Intake
  • Collector: Custom build merge collector
  • ECU: Holley ECU
  • Intake Manifolds:
    • CID Intake: Equipped with a 112mm throttle body.
    • Holley Hi-Ram: Featured a 103mm throttle body, a spacer, the Performance Design carbon lid, and prior porting (though not perfectly matched to the new heads)

Both manifolds were tested under identical conditions to ensure a fair comparison.

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Dyno Results

We recorded torque and horsepower at RPM intervals from 5,100 to 8,800 RPM.

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Analyzing the Performance

CID’s Dominance Across the RPM Range

The CID Intake Manifold showcased remarkable performance throughout the entire RPM spectrum. From the outset, the CID intake demonstrated higher torque figures. At 5,100 RPM, it delivered 678.7 lb-ft of torque, noticeably surpassing the Hi-Ram’s 657.8 lb-ft. This trend continued across most RPMs:

• Mid-Range RPMs: Between 5,100 and 7,800 RPM, the CID maintained a consistent torque advantage.
• High RPMs: As we moved past 8,000 RPM, the CID’s torque advantage became even more pronounced. At 8,800 RPM, it produced 600.4 lb-ft compared to the Hi-Ram’s 565.7 lb-ft.

The CID intake’s design is optimized for high-RPM efficiency, and this was evident in the horsepower numbers:

• Peak Horsepower: The CID achieved a peak of 1,015.3 HP at 8,400 RPM, while the Hi-Ram peaked at 968.2 HP at 8,000 RPM.
• Sustained Power: Even as RPMs increase, the CID maintained higher horsepower figures, indicating its ability to excel in max effort builds.

The CID intake features a larger 112mm throttle body compared to the Hi-Ram’s 103mm. This larger opening allows for increased airflow, which is crucial at higher RPMs when the engine demands more air:

• Better Cylinder Filling: The enhanced airflow ensures that each cylinder receives an optimal air-fuel mixture, improving combustion efficiency.
• Reduced Air Restriction: The design minimizes bottlenecks in the intake path, allowing the engine to “breathe” more freely.

Manifold Absolute Pressure (MAP) is a critical factor in engine performance:

• Higher MAP Readings: Up to 7,800 RPM, both setups had nearly identical MAP KPA data. Beyond this point, the CID intake showed a 2 KPA advantage at 8,800 RPM, indicating less pressure drop and more efficient airflow at high speeds.
• Performance Under Load: The CID’s ability to maintain higher manifold pressure under demanding conditions means the engine can produce more power without straining.

Holley Hi-Ram’s Notable Performance

While the CID intake had some advantages, the Holley Hi-Ram still offered commendable performance:

• Strong Mid-Range Torque: At 6,000 RPM, the Hi-Ram slightly edged out the CID in torque, delivering 682 lb-ft compared to 673.6 lb-ft. This makes it a viable option for street and more conservative builds focusing on lower to mid-range power.
• Cost-Effective: The Hi-Ram can be an attractive and affordable option for those looking for solid low to mid range performance.

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The Verdict

Both the CID Intake Manifold and the Holley Hi-Ram have proven themselves as capable performers on the Gen 5 LT engine platform.

The CID Intake Manifold demonstrated superior performance, making it an excellent choice for applications where mid to high end power is paramount. Its ability to maintain higher torque and horsepower beyond 8,000 RPM showcases its efficiency and suitability for high RPM applications.

On the other hand, the Holley Hi-Ram has proved to be a formidable intake, especially in the low to mid-RPM ranges. Its performance is impressive, considering that its setup was not perfectly optimized for this specific engine. The Hi-Ram’s ability to deliver strong power and torque in the low to mid range RPM ranges makes it a great option for street applications or builds that prioritize mid-range power at the expense of some top end performance.

Ultimately, the “best” intake manifold depends on your specific goals and how you plan to use your vehicle. Whether you’re chasing peak horsepower numbers or seeking a balanced power curve for street performance, both options have distinct merits that can be tailored to your build.