which is the best panel air filter to buy? and does it actually make a difference to performance and sound?
K&N, Courtenay sport, ITG, green filter, not much difference between them in terms of sound or performance. Some are foam, others are cotton and need oiling when they are cleaned.
Will give a tiny gain in performance and responsiveness, won't really effect sound.
i wouldnt go down the cone filter route as you will most likly suffer some heatsoak and loose power rather than gain it
would keep the veccy c pipe and put in a better pannel filter
having tried numerous panel filters and induction kits on vectraa's Cavaliers and now Astra's, i am of the opinion that the standard vauxhall paper element is as good as any. most of the aftermarket panel filters have gaping holes in their filtration medium when held up to the light, which i found very worrying. the only gain to be had with these filters is the fact they can be cleaned and re-used. also if you unpleated the paper element you would see the overall surface area is much bigger compared to say K&N, Pipercross etc. so i concluded that it has much more flow area and when changed regularly, performs as well as any.