For the standard 500 1.4 you could start replacing the filter to a BMC or an ITG in place of the paper filter. You will see then on ebay uk. The next is too fit a CAI system - I would recommend an ITG (discussed on a different thread). The manifold is a restrictor on power - this can be changed to a more free flowing one. The CAT is close to the manifold - some had discussed re-locating further down but the best option from what I have been 'told' is to change it to a pukka sports cat - a less restrictive one. There has been quite a discussion in the UK on 95 octance verus V power i.e. 99 octane - quite a few different opinions - but the higher octane seems to increase the bhp although it would be more remarked on a turbo charged engine (an Abarth) with a esseesse ECU or a piggy back chip from TMC. If you turbocharge the standard 1.4 with the 6 speed gearbox - you will have gearbox trouble - it cannot take the extra power of the turbo. The Abarth in the Fiat 500 (A500) uses a 5 speed gearbox from the Alfa 147. I hear that the US are the first to get the multi-air engines to the dissapointment of Europe ! Also the 1.4 multi-air turbo engine has recently won an award for the best engine in the world !