I admit I have more time than money.

work has some scrap ally, there is some 16mm tube (13mm internal bore) and I think I can fit about 26 of them into a water to air intercooler that will fit in the same place as the original air to air item, plus a radiator obviously, according to my school boy maths the 50mm diameter air pipe has a surface area of roughly 1900 square mm, the pipes in the heat exchanger have over 4500 square mm between them, would that be enough to give an unrestricted flow of air through, or would it slow it down to much and loose pressure?

any help as to whether this is a good idea or not will be very much appreciated, I can make the thing, just not sure if it would be a waste of time or not, I think it should work!