Ive recently given my car to Forge motorsport in Gloucester so that they can develop an upgraded alloy intercooler for the 320d.
They started with the core they use for the 335i (proven gains for that model) and have redesigned it to fit my car (they could probably do this for most 1 or 3 series, but its best to ask them if you have a 330d/335d and are interested).
My car showed a 4bhp increase after the upgrade which may not sound much, but given the low temperatures was actually quite encouraging, it certainly 'feels' quicker and stronger but i'll wait for actual 'normal temp' dyno figures in the spring before stating categorically what the gains are. There should be a larger gain in the spring because an intercooler is more important to lowering the inlet temps (they are lower anyway in the winter).
Forge are a great bunch to deal with and really know their stuff when it comes to motorsport and fabrication. If you have any questions i'll do my best to answer them but im not that technical, so if its in depth please call the development team at Forge, and again for pricing and availability please call their sales office.
I actually forgot to take pics during the process (doh!) but will endeavour to sort some out the next time its up on the ramp, but rest assured the Forge intercooler is much bigger than the oem original.
Tel : 01452 380999