throwing one on a normal road car will make very little difference, But what you might loose in power you could get in torque,
Or you may loose power by 4bhp top line but you could increase mid range power, And like its been said different car different rules the Z isnt a good car for it but a CAI on a turbo car with mapping can make a big difference, and Cars like honda with VTEC it can make a big difference (in comparison to the Z)