Honda Fit GK5—Carbon Fiber Intake Manifold R&D Process

Japanese Car Fan Magazine 📅 Published: Today, 2024-12-05

Development Background

The current generation Honda Fit GK5, launched in China in 2014, is now midway through its lifecycle but remains incredibly popular. With its L15B engine producing 131 horsepower and a curb weight of just over a ton, the GK5 has become a leader in the sporty compact car segment. By tuning the factory ECU to raise RPM limits and optimize fuel injection and ignition timing, the GK5 easily surpasses 100 horsepower per liter, making it a top choice for budget-friendly track enthusiasts.

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Engine power fundamentally comes from air and fuel. Effectively increasing the air intake will result in an immediate and significant boost in power. While the market is filled with various intake upgrade products for the GK5, most are limited to intake boxes upstream of the throttle body. However, when considering the entire intake system, after increasing the flow through the intake box, the intake manifold downstream of the throttle body becomes the bottleneck.

The factory intake manifold design must balance engine performance, fuel efficiency, and NVH (noise, vibration, and harshness). As a result, the GK5’s stock intake manifold has become a significant pain point when seeking to unlock the full potential of the L15B engine.

OEM Analysis

Let’s first analyze the factory design to determine how we can improve upon it.

1️⃣ The GK5 intake manifold inlet has airflow-guiding vanes, and the inlet shape is non-circular. This design organizes airflow to reduce noise. As our design prioritizes performance over intake noise, these features will be omitted.

2️⃣ Air enters the throttle body and flows into a centralized plenum chamber through a long connecting pipe. This ensures even airflow distribution to all four runners. However, this connecting pipe occupies space that could be used to increase plenum volume, which would further enhance engine power.

3️⃣ Honda utilizes space efficiently with its "MM" concept. For example, to the right of the connecting pipe, Honda designed a resonance system to strengthen wave dynamics at low RPMs, enhancing low-end torque. While beneficial for street driving, this feature can be sacrificed for more plenum volume to improve track performance.

4️⃣ The runners are slightly tilted left, likely to avoid the oil cap and timing chain cover, making maintenance more convenient. However, this unconventional tilt complicates carbon fiber manufacturing, increasing production costs.

New Design Goals

After internal discussions, LRPTEC identified several key goals for the new design:

• Increase horsepower by at least 10 HP to make the product competitive.
• Maintain OEM fitment for sensors, lines, and mounting points.
• Avoid interference with surrounding components to simplify installation.

These ambitious goals presented significant challenges to our engineers.

Design Workflow

💡 Precision Modeling
To preserve key OEM features, LRPTEC used industrial-grade 3D scanning to create accurate CAD models of the stock manifold.

💨 Wave Dynamics Optimization
The intake manifold uses wave dynamics to boost power. By fine-tuning runner length, diameter, and plenum volume, we aimed to enhance the powerband at higher RPMs. Using 1D engine simulation software, we validated the design adjustments.

🔧 Iteration Process
After 60+ iterations, the first design prototype was finalized. Flow simulations were used to identify and address areas of turbulence and uneven airflow distribution.

Prototyping and Testing

📈 The first prototype, produced using powder-sintered 3D printing and reinforced with carbon fiber, showed only a 5 HP gain, which was unsatisfactory.

Second Round Redesign:

• Targeted the 7500+ RPM range, as most GK5 race cars exceed the factory rev limit.
• Optimized for aftermarket large-diameter throttle bodies.
• After 20 iterations, the second design yielded a 12.7 HP increase at 6500+ RPM.

Production and Material Choice

LRPTEC chose Toray T300 3K carbon fiber for its superior thermal and mechanical properties. CNC-machined 6061 aluminum was used for mounting points, bonded with aerospace-grade epoxy for durability. 10,000 km of real-world testing confirmed the design’s reliability and consistent performance.

Test Results

📊 Testing configurations included:
1️⃣ Full modifications: +21.1 HP, reaching 194.5 HP total.
2️⃣ Stock engine with aftermarket manifold: +13.5 HP, reaching 167 HP.
3️⃣ Mixed modifications: +16.6 HP, reaching 187 HP.

Summary

LRPTEC’s carbon fiber intake manifold for the GK5 is a result of meticulous design, analysis, and testing. This exclusive product reflects LRPTEC’s commitment to performance and quality. Thank you for supporting our vision to redefine aftermarket engineering!