Finally got my X-1 intake kit from the states. After searching the internet I thought I'd give it a go. Bit pricey, cost £300 in total with delivery, duty and VAT, but is the best you can get for the S4, even MRC recommended it. Can buy them from here, decent guys there, communication was great from them, real helpful. http://sdr-research.com/x1/intake.htm Fitting took a little while as it's a bit of a squeeze, when it was all in the filter was a little squashed, but works just fine. On that subject the filter is an AEM dryflow filter so contains no oils so doesn't bugger up the sensitive MAF. As for the carbon box it's a work of art, really well built and as you can see it uses the stock air feed from behind the grill so gets great airflow to the filter, and come santa pod time out will come the headlight for even more air directly onto the cone! SDR claim the X-1 measured half the pressure drop of the RS4 airbox. Also comes with a machined aluminium plate and self tappers to relocate the ignition heatsinks from the top of the original airbox to the suspension turret or bulkhead. Well anyway here's a few pics of the parts going in and the finished product fitted. The airbox fitted. Gorgeous! Seals perfectly against the bonnet to keep any hot air out. With cone fitted. Can just about see here the use of the standard air feed, can make out the filter through it.