Often with cars when you pull up after a blast and there is a lot of heat in the block it then results in localised boiling if you switch off too soon as the water pump isnt moving the water around anymore, so if a bit of the block is hot that heat ends up in only the water that happens to be sat next to it at the time you switch off, likewise if there is heat in the turbo it can do the same thing.
This is why its important to do a cooldown lap, or leave the car ticking over for a while before switching off (not just this car, any car TBH)
Not saying that is the case with this car and that is the only reason its doing it, it might not be, it could well be the sign of a bigger issue, Ive not been near it for a couple of months, but just saying its a possible explanation as to why there would be some bubbling after switchoff if it had just been driven hard and not allowed to cool properly first.
As per Fred I would want to fit a better radiator anyway, its not ever been used in the summer months since the conversion so although the radiator has coped fine in terms of controlling coolant temps so far, it doesnt mean it will cope on a hot July day.
For the record, im quite good mates with Jack and Mike, but I have utterly no interest in wether he sells the car or not, nothing to do with me, so just giving my honest opinion based on my experience of it.
As I mentioned on the phone, I'm quite happy to do some more mapping on it as the coldstart mapping hasnt yet been done properly (needs to be done over a period of a few days and I did all the mapping in one evening and always intended to revisit it to finish it off but we just havent got round to it), but also as mentioned on the phone although there is undoubtably the scope to make more power I'm not up for mapping it for more power as me and Mike both believe that it will risk becoming unreliable if pushed harder, 260bhp was always the intended output figure and neither of us has any interest in pushing it further.
The engine to the best of my knowledge has NOT had a full rebuild as mentioned in this thread by millerin etc, it had a strip down which is where millerin will have seen it in bits (he's always in and out down the workshop as he is mates with them), it then had an inspection and rebuild with some new parts like head gasket etc, but pistons are the original 100K miles old ones etc not new.
It has been very reliable in the time Jack has been using it, but you have to go into something like this with your eyes open to the fact that its a high milage standard engine with now nearly double the standard torque figure, so its obviously going to wear out at some point, and likewise adding a turbo is another thing to maintain etc, so dont assume that just beause it has been done well that it means its going to last forever, its an ex development car not a new car with a warranty etc.
P.S
Jack used to be part of MWM, he has now moved to Stone, Stone had nothing to do with building the car, it was done by MWM while Jack was still there.
Its not being sold by Stone or MWM though, its just Jack selling his own car which happened to be use as a development car by MWM. So I would approach it with the same caution as any unwarrantied private sale.