Dun worry... in fact the seemingly quicker acceleration should
be the K&N filter enabling cleaner air to be fed into your
engine hence improving the performance. In essence, i think that
its mostly psychological. One way you can prove that its truly
working is use the filter for a while, then remove it. This is a
better way to see if the filter is REALLY improving your
acceleration. There are instances where bhp actually falls, but
torque goes up, but thats another chapter. But sorry I
digress...
Unlike the usual stock filter which is made of paper, aftermkt
filters (of which K&N is pretty popular and established)
actually improve air flow and air filtration. Hope this helps.