I got to do some airflow testing on a 2001 330ci yesterday. Was curious to see how well the new 3 liter engine flowed. Testing was performed as always with OBDTOOL recording RPM and mass air flow. We performed 4 second gear runs with DSC disabled and merged the data points together for a smoother curve.
The air temperature at the filter was 35 degrees.
From the graph it looks like the engine breathes well down low all the
way through the midrange but starts dropping off a little under 6k. Calculating
volumetric efficency results in
RPM VE
1300 = 95%
1500 = 100%
1800 = 97%
1900 = 97%
2200 = 99%
2500 = 100%
3000 = 106%
3500 = 104%
4000 = 105%
4500 = 106%
5000 = 103%
5500 = 101%
5800 = 101%
6000 = 96%
6100 = 95%
6200 = 94%
6300 = 94%
6500 = 93%
From this we can see the engine breathes well down low which would lead you to expect the engine to have good low end torque which it does. Peak breathing is between 3000-4000 rpm this would correspond to peak torque which it also does. The flow starts dropping off at around 5500 though and is down quite a bit at the rev-limiter. So something in this engine is restricting airflow.
The design of the airbox is interesting. It has two smaller feeds into it but from the main feed the air needs to make a 90 degree turn to head down then a 180 degree turn to head back up through the filter. If I can find a used airbox for this car I will see if I can increase the flow.
Theoretically, this engine could produce around 264hp if we could keep
the airflow (torque) perfect to 6500 rpm.
HP = (torque*RPM)/5252.
264 = (214*6500)/5252
Probably won't be able to do that of course though.