Ben, the collector, i didnt want to mention it as well......i can be seen to criticise and look down on people all the time by some.
ANyway, since Chris pointed it out, you have no uniform pattern for the collector. Its not creating any sort of flow direction, they all just converge in that tiny plenum and especially around cylinders 2-3, ill be pressurerised and possibly create flow reversal around overlap in cylinders 2-3. WHere it all meets each primary pipe is pointing in a different direction, i know space is limited but ideally they would taper slowly to the turbo flange and all follow the same direction for about a foot.
The cast item is horrid......plain horrid, but it comes form some company in Europe as does the whole conversion i think. Come to think of it, have they got a turbo profile cam to run or do they keep it std?
Oh, and apart from the ceremic coating which has been mentioned (ill try find the number of the UK operation, states is better as they have far more choice) you could use a simple turbo blanket cover on teh turbine to try minimise heat tranfer as its so close to the bulkhead/mastercylinder.