:?: Does anyone now what the diffrenc is betwen cast iron gt40 heads and the alloy ones (other than the material there made of) and can they flow the same :?:

Same basic design, the alloys flow a little better out of the box. There are also a number of different versions, in cast there is the GT40 and GT40P's while in alloy there are GT40Y and GT40X's.

Flow specs are: (intake/exhaust cfm)
GT40 - 192/128
GT40P - 198/139
GT40Y - 213/134
GT40X - 226/161

The GT40 and GT40P's can be ported fairly easily and can flow similar specs to the alloys, I have a set of ported GT40P's which flow 235/175 cfm and there is still probably a bit left in them.

So how easy are the X and Y heads to obtain compared to the cost of porting a set of P's?

By the time you buy and port the GT40P's you will probably have spent the same as getting some of the GT40X's over from the US (around $2k I would imagine). But if you need that sort of flow I would be looking at a set of Edelbrock, Trickflow or AFR alloys.

The x303's can be bought for 2200 up here in QLD at raceparts australia.

If you want y303's a mate of mine might be selling some for about 1700-1800...i think its about that