Code No. 33004-AH003
Unlock the Full Potential of the HKS Metal Catalyzer with the New HKS Front Pipe!
■Features
- When the HKS Metal Catalyzer is installed, the diameter of the factory front pipe becomes a restriction to exhaust flow. To eliminate this bottleneck, HKS has developed a dedicated Front Pipe.
- Designed to optimize the connection between the HKS Metal Catalyzer and either the HKS exhaust system or the stock exhaust, this front pipe further reduces exhaust back pressure and maximizes exhaust flow efficiency.
- In addition to improved performance, the front pipe delivers a sportier exhaust note for a more engaging driving experience.
- Manufactured using high-quality TIG welding, the pipe features carefully finished flange joints to minimize flow disruptions caused by stepped pipe transitions, while also providing a clean, premium appearance.
■Components
| Material | SUS304 | |
| Pipe Diameter | Φ74.7 | |
| Sound Level (At Idel) | ||
| Stock Exhaust | LEGAMAX Sports | |
| Stock Catalyst | 81dB (59dB) | 91dB (71dB) |
| HKS Catalyst | 85dB (63dB) | 93dB (72dB) |
| Minimum Ground Clearance | 115mm (Stock Front Under Panel) | |
| Product Weight | 3.2kg (Stock: 4.5kg) | |
*LEGAMAX Sports (31021-AH005)
●Pipe Layout
Compared with the stock layout, the pipe diameter and bend angles have been optimized for improved exhaust flow.
Through repeated testing, HKS minimized the number of pipe joints to eliminate even minor steps and restrictions in the exhaust path. The increased pipe diameter further reduces exhaust back pressure, achieving a more efficient exhaust flow.
HKS Front Pipe
Stock Front Pipe
●Performance
Flow bench testing showed that, when combined with the HKS Metal Catalyzer (hereafter referred to as the “HKS Catalyzer”), the HKS Front Pipe reduces exhaust resistance by approximately 5–10% compared with the stock front pipe.
When combined with the HKS LEGAMAX Sports Muffler (hereafter referred to as “LMS”), exhaust resistance is reduced by up to 23% (④ in the table).
*With the stock muffler: 5% reduction (②) / With the LMS: 10% reduction (comparison between ③ and ④)
*Graphs and values are based on in-house testing. Results may vary depending on product variation and measurement equipment.
| Reduction Rate [%] | |
| ①HKS Catalyzer + Stock Front Pipe + Stock Muffler | - |
| ②HKS Catalyzer + HKS Front Pipe + Stock Muffler | 5 |
| ③HKS Catalyzer + Stock Front Pipe + HKS LMS | 13 |
| ④HKS Catalyzer + HKS Front Pipe + HKS LMS | 23 |
Point
Reduced Exhaust Resistance Through Smoother Pipe Bends and a Stepless Layout
The stock front pipe is designed with a relatively small diameter to match the stock catalyst, which can become a bottleneck when upgrading to a high-flow catalyst. To eliminate this restriction, the HKS Front Pipe is designed with smoother pipe bends and seamless transitions at both the front and rear flange connections, minimizing steps in the exhaust flow path.
●Performance Comparison
– HKS Catalyzer + HKS Front Pipe (HKS FP) + Stock Muffler
*Graphs and values are based on in-house test results. Results may vary depending on the vehicle and measurement equipment.
*Values shown in the table are rounded.
| Configuration | Maximum Power (kW(PS)/RPM) |
Maximum Torque (Nm(kgf･ｍ)/RPM) |
| Fully Stock | 243(330)/6600 | 420(42.8)/3800 |
| HKS Catalyzer + Stock Front Pipe + Stock Muffler |
250(340)/6600 | 439(44.8)/3900 |
| HKS Catalyzer+ HKS Front Pipe + Stock Muffler |
255(347)/6400 | 446(45.5)/4000 |
| Test Vehicle | CIVIC TYPE R (6BA-FL5) |
| Specification | METAL CATALYZER 33005-AH006 (HKS Catalyzer) HKS Front Pipe 33004-AH003 Stock Muffler R-TYPE INTERCOOLER 13001-AH007 |
Even with the HKS Catalyzer and factory muffler combination, replacing the factory front pipe with the HKS FP reduces exhaust resistance and delivers increased power across almost the entire engine speed range. In HKS in-house testing, the maximum gains were:
Power: 9(12)/5300 (kW(PS)/rpm)
Torque: 21(2.1)/3300 (Nm(kgf・ｍ)/rpm)
●Performance Comparison
– HKS Catalyzer + HKS Front Pipe (HKS FP) + HKS LEGAMAX Sports (HKS LMS)
*Graphs and values are based on in-house test results. Results may vary depending on the vehicle and measurement equipment.
*Values shown in the table are rounded.
| Configuration | Maximum Power (kW(PS)/RPM) |
Maximum Torque (Nm(kgf･ｍ)/RPM) |
| Fully Stock | 243(330)/6600 | 420(42.8)/3800 |
| HKS Catalyzer + Stock Front Pipe + HKS LMS |
255(347)/6600 | 439(44.8)/3900 |
| HKS Catalyzer + HKS Front Pipe + HKS LMS |
258(351)/6500 | 455(46.4)3900 |
| Test Vehicle | CIVIC TYPE R (6BA-FL5) |
| Specification | METAL CATALYZER 33005-AH006 (HKS Catalyzer) HKS Front Pipe 33004-AH003 LEGAMAX Sports Muffler 31021-AH005 (HKS LMS) R-TYPE INTERCOOLER 13001-AH007 |
Even with the HKS Catalyzer and LEGAMAX Sports combination, replacing the factory front pipe with the HKS FP reduces exhaust resistance and delivers further power gains across almost the entire engine speed range. In HKS in-house testing, the maximum gains were:
Power: 9(12)/3400 (kW(PS)/rpm)
Torque: 25(2.6)/3400 (Nm(kgf・ｍ)/rpm)
●Performance Comparison
– HKS Catalyzer + HKS Front Pipe (HKS FP) + HKS LEGAMAX Sports (HKS LMS) + Power Editor R
*Graphs and values are based on in-house test results. Results may vary depending on the vehicle and measurement equipment.
*Values shown in the table are rounded.
| Configuration | Maximum Power (kW(PS)/RPM) |
Maximum Torque (Nm(kgf･ｍ)/RPM) |
| Fully Stock | 243(330)/6600 | 420(42.8)/3800 |
| HKS Catalyzer + HKS Front Pipe + HKS LMS |
258(351)/6500 | 455(46.4)3900 |
| HKS Catalyzer + HKS Front Pipe +LMS+PER |
272(370)/6200 | 484(49.4)/3800 |
| Test Vehicle | CIVIC TYPE R (6BA-FL5) |
| Specification | METAL CATALYZER 33005-AH006 (HKS CAT) HKS Front Pipe 33004-AH003 (HKS FP) LEGAMAX Sports Muffler 31021-AH005 (LMS) R TYPE INTERCOOLER 13001-AH007 Power Editor R 42018-AH015 (PER) |
Adding the PER to the HKS Catalyzer + HKS FP + LEGAMAX Sports combination unlocks even greater power potential. In HKS in-house testing, the maximum gains were:
Power: 21(29)/5700 (kW(PS)/rpm)
Torque: 38(3.9)/4300 (Nm(kgf・ｍ)/rpm)
●Sound Comparison – Frequency Analysis of Exhaust Noise
Installing the HKS Front Pipe also changes the exhaust sound characteristics of each muffler combination.
・HKS Catalyzer ＋ HKS Front Pipe ＋ Stock Muffler
→ Retaining the characteristics of the factory muffler, the exhaust note becomes a clear,
refined sport sound with a controlled low-frequency tone.
・HKS Catalyzer ＋ HKS Front Pipe ＋ LEGAMAX Sports Muffler
→ Delivers a powerful, more aggressive and race-inspired exhaust note with a strong
presence across the entire frequency range, from low to high frequencies.
For measured sound pressure levels (dB) for each combination, refer to the table below.
| Combination | Proximity Exhaust Sound (dB) |
| HKS Catalyzer ＋ HKS Front Pipe + HKS LEGAMAX Sports | 93 |
| HKS Catalyzer ＋ HKS Front Pipe + Stock Muffler | 85 |
| Stock Catalyzer ＋ HKS Front Pipe + HKS LEGAMAX Sports | 91 |
| Stock Catalyzer ＋ HKS Front Pipe + Stock Muffler | 81 |
| Stock Catalyzer ＋ Stock Front Pipe + Stock Muffler | 84 |
*HKS Catalyzer…HKS METAL CATALYZER (33005-AH006)
*HKS Front Pipe…(33004-AH003)
*LEGAMAX Sports…(31021-AH005)
* Graphs and values are based on in-house test results. Results may vary depending on the vehicle and measurement equipment.
| Vehicle | Model | Engine | Model Year | Material | Pipe Size | Consist of | Code No. | Manual | Remarks |
|---|---|---|---|---|---|---|---|---|---|
| CIVIC TYPE R | FL5 | K20C | 22/09 - | S3 | Φ74.7 | 1 | 33004-AH003 |
|
Estimated replacement time: 1–2 hours. |
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