basically said:
when we were doing the mapping on my car which has a k03 turbo, standard bottom end & a head that has been ported and has 31mm exhaust valves, Robin was doing mapping on his too. We hired a rolling road for a few hours to get the maps finished off properly and do power runs. Robins car is the same spec but 1341cc bottom end with a standard head. Both cars made almost exactly the same peak power (mine was actually 0.2bhp more haha unlucky Robin!). robins made more power in the mid-range thanks to the extra cc's and increased compression ratio. But his ran out of steam in the high RPMs whereas mine carried on increasing power thanks to the head capable of flowing more.
So yeah they definitely make a difference, to an otherwise standard G40, probably not so much but if you are increasing the boost significantly then it's a good idea.
