Supposedly Jap Performance are reporting on some test done at the Scooby clinic.....
"In the coming edition of Japanese Performance magazine there will an interesting feature on a group test of panel panel filters...
Conducted at Scooby Clinic, using their Dyno Dynamics rolling road, air intake temperature remained the same (16-17°C) and two power tests per filter were taken
All filters were tested all of the performance panel filters on a 54-plate Impreza WRX STi 2.0-litre, which was originally fitted with a standard panel filter. The standard panel filter was in reasonable condition, showing dirt on roughly half the face of the paper pleats.
Filters tested were:
K&N
ITG
Pipercross
Green
Cosworth
Do Luck
The results? The pre-oiled Do-Luck foam filter
Gave a max BHP of: 297.7 (12.9 BHP extra over the stock filter). Its nearest competition was K&N which gave 10.4 bhp more..."
Obviously these tests weren't done on a zed but it gives me enough info to think about trying it out - although I've had the K&N in for the last 9k miles for the sake of £30 I'm not faffing around trying to clean it and oil it