I don't into a cone filter benefiting any otherwise stock car, and here's why: (BEW for example)
Diesel operates on a fuel throttle, not air. More fuel= more power, period. More fuel is the only way to make more power. The lambda (a/f ratio) varies widely, from 0.8 to 10 (these are factory ecu calibration limits, anyway). Diesel does not require a fixed (stoichiometric) air/fuel ratio, so adding more airflow without fuel won't add power, especially when you are already running "lean" in gasser terms. Yes, it has a lambda sensor, but it doesn't serve the same function in the same way as a gasser. At full load, the lambda map(s) is/are a fuel limiter, not a fuel/air ratio regulator.
The max power the factory setup can make, with the factory ecu calibration, is NOT airflow limited, it is limited by the 2d torque map at full throttle. (yes, I know it's really 3d, but let's pretend it acts like a 2d map for the sake of argument). Once you hit about 85% throttle position it's done, no more fuel (power) for you, in the factory calibration. At high altitude it's less throttle before you hit the limit. The smoke map(s) stops being limiting at full throttle, by design, about 2500 rpm. From then on up it's what's commonly referred to as the "torque" map that limits full power.
You can observe this by data logging vag-com measuring blocks group 8, which displays the torque request alongside the rpm/altitude limiter and the "smoke" limit.
Group 3 will show the airflow. EVEN IF the new filter did somehow increase the max airflow, it wouldn't matter for making more peak power, because airflow is not limiting above 2500 rpm IN A CAR WITH FACTORY ECU
THERE IS ABSOLUTELY NO BENEFIT TO AN OTHERWISE COMPLETELY STOCK CAR
There MIGHT be an argument to be made about better turbo spool at lower rpm, or maybe better torque at lower rpm, IF you can show a shift in the MAF-based fuel limiter to max out at a lower rpm, for example.
You could say there's less smoke in a stock car "before the turbo spools", which is immaterial with a properly operating VNT and maf sensor
You could even argue the benefits for turbo safety in a tuned car, (lower pressure ratio for the compressor due to "less restriction" -what a lovely catchall phrase that is), but if you don't improve the intake tract after the maf (OMI) then you still haven't fixed the problem.
You might could say smoke is reduced in a tuned car, but unless you are maf-limited it won't matter, any way.
If there is a dyno showing a benefit, I would tend to suspect the test car had a bad maf, or something similar. There have been numerous dynos of completely stock BEW at very close to the rated HP/TQ of 100 hp and 177 ft-lb. (VW rates these cars at the wheels) It looks like the second dyno is a healthy, stock car.
Boost pressure is ECU regulated, stock boost, stock airflow. Maybe the turbo doesn't require as much drive pressure to make the boost, resulting in a better delta and a reduced vnt angle, better overall efficiency? Maybe a little, but not 15% gain. Any gain will tend to get lost in the statistical noise.
There are benefits to be had for a modified car, but stock, no way will you see any appreciable magnitude of gains.
