Report:

Zero/Sports® 76 mm Air Intake Kit, World League Cat-Back
&
EDO cat-less Down-Pipe
&
Recalibration of the Engine Control Unit
on 2007 Subaru STi

Prepared by: EDO Performance, LP 16182 Gothard St, Unit P Huntington Beach, CA92647
www.edoperformance.com

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 THEORY & BACKGROUND

3.0 METHODOLOGY & PARAMETERS

3.1 METHODOLOGY

3.2 PARAMETER

4.0 RESULTS & ANALYSIS

4.1 RESULTS

4.2 ANALYSIS

5.0 IMPLICATIONS

REFERENCES

1.0 INTRODUCTION

The goal of the experiment was to quantify the gain of horsepower (HP) in a 2007 Subaru WRX STi from the installations of Zero/Sports® 76 mm Air Intake Kit, Zero/Sports® World League Cat-Back and EDO cat-less Down-Pipe and the recalibration of the Engine Control Unit (ECU).

2.0 THEORY & BACKGROUND

The function of air intake is to introduce cold air into the internal combustion engine to increase the engine power [1]. It may also increase the life of the engine and fuel economy of the car. In principle, the air intake maximizes the amount of oxygen available to the engine for combustion with fuel by introducing “cold” air into the engine because cold air has higher density for a given volume. However, the term “cold” air does not always literally mean cold air. It can also mean introducing higher amount of oxygen to the engine. Most of cold air intakes have the following design:

• Larger diameter of the intake
• Smooth interior of the intake for less resistance
• Better direct route to the intake
• Optimizing the length of the intake to maximize airflow at certain RPMs
• Using less restricting air filter
  

Cat-Back refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent to open air. The design of the cat-back is usually large pipe diameter that allows the gas to exit with as little back-pressure as possible such that not restricting the power of the engine [2].

The design of downpipe is to provide better flowing unit of exhaust gas. This usually
achieved by its larger diameter of the exhaust.

ECU Controls various aspects of a car’s internal combustion operations. At its simplest form, the ECU controls the quantity of injected fuel to the engine cylinder at each engine cycle [3]. With advances in technology, most ECU controls the ignition timing, variable valve timing, level of boost maintained by the turbo charger and other peripherals. These controls are monitored by sensors located on different parts of the engines.

3.0 METHODOLOGY & PARAMETERS

All experiments were completed at sea-level altitude and average humidity of 30%. The
average outside temperature was 860F.

3.1 Methodology

Dynapack 5000® Dynamometer was used to measure the wheel-horsepower (WHP) and the ECU of the car was reset before each configuration to eliminate skews in the dynamometer reading. The horsepower reading was calculated from the average of three dynamometer pulls of each configuration.

3.2 Parameters

Configuration 1: (Baseline): Original 2007 Subaru WRX STi

The 2007 Subaru WRX STi was purchased on December 2007 with its original settings (Factory ECU Calibration) and hardware intact.

Configuration 2: Stock Exhaust Installation of Zero/Sports® 76 mm Air Intake

From configuration 1, the original air intake was removed and replaced with Zero/Sports® 76 mm Air Intake Kit. The following items were included in Zero/Sports® air intake kit:

Zero/Sports® air filter 76 mm pipe and silicon hoses Metal clips Other fitments

Figure 1. Zero/Sports Air intake kit

Configuration 3: Stock Exhaust with Cat-Back removal

From configuration 2, the Zero/Sports® Air Intake Kit was removed and the original intake was re-installed to the car. In addition, the original Cat-Back was removed from the car.

Configuration 4: Stock Exhaust with Zero/Sports® World League Cat-Back

From configuration 3, Zero/Sports® World League Cat-Back was installed as an addition. Zero/Sports® cat-back was made of steel with diameters of 2.5”, 8” and 4” of tubes diameters respectively as shown in figure below.

Figure 2. Zero/sports World League cat-back

Configuration 5: Zero/Sports® Cat-Back with Cat-Less EDO Downpipe

From configuration 4, the original downpipe was removed and replaced with EDO Performance Cat-Less Downpipe which had 3” diameter with bell-mouth design.

Figure 3. EDO Cat-less Down pipe

Configuration 6: Zero/Sports® 76 mm Air Intake, Zero/Sports Cat-Back and Cat-Less EDO Downpipe

From configuration 5, the original air intake was removed and replaced with Zero/Sports® Air Intake Kit.

Configuration 7: ECU Recalibration

From configuration 6, the factory calibrated ECU mapping was recalibrated using TurboXS® Utec.

4.0 RESULTS & ANALYSIS

4.1 Results

Configuration 1: Original 2007 Subaru WRX STi

Figure 4. Configuration 1 graph

With original settings and hardware, the 2007 Subaru WRX STi registered 240.2 wheel-HP at 5700 RPM.

Configuration 2: Stock Exhaust Installation of Zero/Sports® 65mm Air Intake

Figure 5.Configuration 2 graph

With Zero/Sports® Air Intake, the car registered 258.9 wheel-HP, a gain of 18.7 HP.

Configuration 3: Stock Exhaust with Cat-Back removal

Figure 6. Configuration 3 graph

With the removal of cat-back from the original setting, the car registered 245.8 peak wheel HP, a gain of 5.2 HP.

Configuration 4: Stock Exhaust with Zero/Sports® World League Cat-Back

Figure 7.Configuration 4 graph

With the Zero/Sports ® Cat-Back, the car registered 243.5 peak wheel-HP, a gain of 3.3 HP.

Configuration 5: Zero/Sports® Cat-Back with Cat-Less EDO Downpipe

Figure 8. Configuration 5 graph

Combination of Zero/Sports® Cat-Back and EDO Cat-less downpipe registered peak wheel horsepower of 248.2, a gain of 4.7 HP from configuration 5.

Configuration 6: Zero/Sports® Intake, Zero/Sports Cat-Back and Cat-Less EDO Downpipe

Figure 9. Configuration 6 graph

With the addition of Zero/Sports ® Air Intake, the car registered peak wheel horse power of 277.9, a gain of 29.7HP.

Configuration 7: ECU Recalibration

Figure 10. Configuration 7 graph

Finally, a combination of configuration 6 and ECU recalibration, the car registered a 291.1 peak wheel horsepower, a gain of 50.9 HP from stock Subaru WRK STi.

4.2 Analysis

The following table summarizes the results of the experiment.

Additions	Peak HP	RPM	Gain / Loss (HP)
Original WRX Sti	240.2	5700	-
Zero/Sports 65mm Air Intake	258.9	5800	18.7( From stock)
Stock Exhaust & Cat-Back removal	245.8	5800	5.2 (From stock)
Stock Exhaust & Zero/Sports Cat-Back	243.8	5600	3.8 (From stock)
Zero/Sports Cat-Back with EDO Cat-Less Downpipe	248.2	5900	4.4
Zero/Sports Air Intake, Zero/Sports Cat-back and EDO Down pipe	277.9	6000	29.7
ECU recalibration	291.1	5200	50.9 ( From stock) 13.2

Table 1. Summary of results from different configurations

Based on the modifications implemented to the 2007 Subaru WRX STi, the addition of Zero/Sports® 65mm Air Intake provided the biggest boost of peak wheel horsepower (WHP) at 18.7, about 8% over stock. The additions of Zero/Sports Cat-back and EDO Cat-Less downpipe provided smaller gain of peak WHP at around 2% over stock. However, replacing the stock Cat-Back with Zero/Sports® Cat-Back would free more power from stock configuration, about 1.5%. A combination of Zero/Sports® 65mm Air Intake, Cat-Back and EDO downpipe showed an improvement of 12% in power.

Before the recalibration of the ECU, most of the gain in power was achieved at higher RPMs than when the car was in stock configuration. It was an achievement of power at a significant economy loss to the engine. After the ECU recalibration, the power produced was 21% higher over stock configuration and the power was achieved at 5,200 RPM, lower than in stock configuration.

5.0 IMPLICATIONS

From the experiment, building a balanced performance car requires combinations of hardware and software recalibration. A gain of power at an economical cost would be the addition of an air-intake as shown in configuration 2. By adding a 65mm air-intake and without recalibration of the ECU, the car achieved gain of 7.8% over stock configuration at slightly higher RPMs. Recalibration of the ECU to suit the hardware modification(s) is essential in achieving higher peak power at lower RPMs.

REFERENCES

[1] http://en.wikipedia.org/wiki/Cold_air_intake, Cold Air Intake, September 14, 2008

[2] http://en.wikipedia.org/wiki/Exhaust_system, Exhaust System, September 29, 2008

[3] http://en.wikipedia.org/wiki/Engine_control_unit, Engine Control Unit, October 4, 2008

[4] http://www.zerosports.co.jp/shop/index.php?main_page=product_info&products_id=129, Zero/Sports ® Racing Development, October 6, 2008

[5] http://www.zerosports.co.jp/shop/index.php?main_page=product_info&products_id=543, Zero/Sports ® Racing Development, October 6, 2008

[6] http://shop.edoperformance.com/edo-hiflow-catless-downpipe-wrxsti-p-9844.html, EDO Hi-Flow cat-less down pipe, October 6, 2008