[DaveW]

Ben is correct, IM240 is a driving 4 minute (....240 sec) test where the driver follows a simulated throttle on/off, cruise, RPM, and load over time cycle.
Attached emissions equipment captures the emissions output measurements during the test.

The measurements are then compared to the relevant ADR37/xx requirements for a pass/failure result.

I have discussed with several tuners as i work towards my ECU selection,
The key components of the output is Tune, Cam, Compression. O2 sensors, not throttle bodies or ignition system.
The induction side...# of throttle bodies will have no effect on emissions provided the fuel A/R is tuned appropriately, the issue for big throttle bodies, is the ratio of opening to pedal movement affecting large TB, and multiple large TBs, vehicle drivability.....chime in here Gav...
The CAM and O2 sensors seem to be the issue. The wilder the cams, the more total unburnt hydrocarbons TUHC produced at the relatively low rpm scale used on the IM240 test cycle.
The leaner you go to correct this, elevates the NOx and you fail at this measurement.
I'm told that good wide band O2 sensors are a key factor in the ability (speed) of the ECU to react to changed conditions and that most vehicles fail the IM240 at the throttle chop and accel points in the drive cycle.

This is all I've learnt so far, but suffice to say, there is a good chance you will pass provided the CAM is from something relatively mild and the tuner is on the ball.

Dave