The E9X series airbox system is a brilliantly designed intake with an excellent flow path and feed system for ambient air. However, upon closer inspection, there are restrictions in the inlet tube that connects the airbox to the intake manifold. By redesigning the tube while retaining the airbox, we were able to allow the V8 engine to breathe more efficiently and therefore make more power. In addition to the new tube design, we also identified a further restriction in the air feed system. To overcome this, we designed a scoop to allow increased airflow through the airbox. This further reduces inlet temperature readings and increases system performance.
The Eventuri E9X M3 intake system is made up of a series of components designed to perform a specific purpose and manufactured to the highest standards. Here are the details for each component and the design ethos behind them:
Each suction system consists of:
- Carbon Fiber Intake Pipe
- High Flow Urethane Cone Filter
- Fiber Air Intake carbon
- CNC machined breather adapter
- Laser cut stainless steel debris guard
- OEM spec silicone joint and clamps
Dyno performance increase: 8-10hp, 10-12ft-lb
Dyno testing was done that showed a consistent gain of around 9 hp and 11 ft-lb of torque. The gain is not just at peak, but throughout the rpm range. On the street, this translates to more response at mid and full throttle with the car pulling much more eagerly towards the redline. The tests were run on the same day back to back and temperatures were monitored to ensure consistency. The car was tested first with the stock intake and hood closed. We then left the car on the dyno and installed the Eventuri. The car was then run again with the hood closed. Several tests were performed with both configurations to obtain a consistent result.
Improved performance on road Dyno (Insoric): 16 HP, 14 Nm
The system has been tested even using a road measuring device (Insoric). On the road, the airflow is much better than what the fan can achieve on the dynamometer and so the intake system is able to perform better. The following graph shows the difference the Eventuri intake makes on the road compared to the stock airbox. The measured gains were 16 HP and 14 Nm: the solid lines indicate the Eventuri and the dotted lines indicate the stock airbox. The red line indicates the power at the crankshaft and the blue line indicates the wheels.
Data logging flow and input temperature
To monitor and log the data output from the ECU, we used a Bavarian Technic diagnostic tool. The car was fitted with the stock system and so the data was recorded in 4th gear up to redline. The Eventuri intake was then fitted and the same method was applied. The outputs show that the mass airflow with the Eventuri is greater across the entire rpm range, with a greater difference at higher rpm where the restrictions in the stock system become more apparent. Additionally, the difference between ambient temperature and inlet air temperature (IAT) is also less with the Eventuri, because the scoop allows for a higher air velocity through the airbox. Here are 2 screenshots of the data output, one at around 5000 rpm and the other at around 8300 rpm.
Data logging summary:
- IAT difference at 5000 rpm vs ambient: stock intake = 9.6 degrees C : Eventuri = 5.3 degrees C
- IAT difference 8300rpm with ambient: stock intake = 7.6 degrees C : Eventuri = 4.7 degrees C
- Air mass flow rate at 5000 rpm: Stock intake = 635 kg/h : Eventuri = 650 kg/h
- Air mass flow rate at 8300 rpm: Stock intake = 1168 kg/h : Eventuri = 1202 kg/h
Test VBox acceleration
Finally we took the car for some road testing using a Vbox unit to record acceleration from 60-130mph (also 100-200km/h). For the Vbox tests our test car had a primary decat and stage 2 tune for all test runs. Tests were performed on the same stretch of road, always on the same day to minimise variables. The results show that with just the added intake, acceleration times from 60-130 mph and even 100-200 km/h were reduced by around 0.3 seconds, which is a significant change at those speeds.
Acceleration results summary:
- 60-130 mph with standard aspiration = 11.157 seconds
- 60-130 mph with Eventuri aspiration = 10.886 seconds
- 100-200 km/h with standard aspiration = 9.56 seconds
- 100-200 km/h with Eventuri intake = 9.236 seconds
Carbon intake tube
The intake tube has been designed to improve the airflow path compared to the stock tube, from the filter to the manifold. It is a one-piece design that has no internal interfaces and therefore provides a much smoother path for the airflow to negotiate. Additionally, the geometric transition is from a circular opening for the filter to the oval outlet for the manifold. This is a much more efficient shape change than the stock pipe which must go from a rectangular opening for the filter to an oval outlet for the manifold.
The stock intake pipe has 2 accordion sections which are used to allow the pipe some flexibility for the movement of the engine. These sections introduce more internal interfaces to the incoming airflow which results in turbulence and therefore a less efficient path for performance. The Eventuri pipe, on the other hand, has zero internal interfaces and so the airflow can remain laminar, which allows the engine to breathe more efficiently.
Another disadvantage of the stock pipe is the large internal face at the stock filter connection. This exposed wall causes the airflow to circulate as it enters the tube from the filter due to the abrupt change in geometry from the rectangular opening of the filter to the more oval shape of the tube.
Flexibility and Movement
A major challenge to overcome was the requirement for movement with the engine. Rather than using silicone joints with flexible sections (which would have introduced interfaces similar to the stock hose), we designed the hose itself so that it could move with the engine. The hose has a compressible neoprene band around the section that interfaces with the stock airbox. This section seals the hose to the airbox but allows movement in and out of the airbox as the engine moves. By allowing the tube itself to move, we were able to create the smoothest flow path possible.
Air intake carbon
The E9X M3 airbox system is saturated with cold air from 2 supplies: one supply lower feed from under the headlight and a top feed from behind the kidney grilles. The primary feed is the lower one from under the headlight as it connects directly to the airbox with minimal change of direction and a large opening to the airbox. This is also a high pressure area of the car and the airflow moves through the airbox from underneath to the outlet at the top which connects to the outlet vent in the bonnet. The other feed is from behind the kidney grilles which although a welcome addition provides a much lower volume of air to the airbox than the lower feed. This is because the airflow has to change direction 90 degrees twice and also because the ducting narrows significantly before entering the airbox.
Looking closer at the lower duct, it becomes clear that the duct has a large ridge that comes back on itself just before the airbox opening. This acts as a barrier that inhibits direct airflow entry into the box by reducing the airflow inlet velocity.
By designing a scoop to sit over the stock duct and curve first to eliminate this ridge, airflow can now pass from the duct to the airbox without restriction.
The airflow path is much smoother, and as a result, the velocity of the air entering the airbox is greatly increased. This allows intake temperatures to be lower than without the scoop – we’ve recorded on-road IAT data where we were able to reduce intake air temperature by 2 degrees using the scoop. To illustrate the effectiveness of the scoop, we devised a simple experiment using a leaf blower to generate flow and an air velocity meter to measure the velocity of the air entering the airbox. We fixed the blower in a position so that it pushed air directly into the lower duct and placed the meter inside the airbox to measure the incoming velocity. The results showed a significant increase in velocity of almost 50% when using the scoop. The full video of the test can be seen in the Video tab.
Debris Shield
The final component is a debris shield attached to the filter, which deflects debris and water from directly impacting the filter. With the increased airflow entering the airbox with the scoop, this is a major addition. There is no negative impact on performance as the airflow is not impeded through the airbox, temperatures are still lower than stock.
