I would personally say that was the nitrous that caused that

it can make a mess of anything and looks like he was lucky.

odd how Steve only said to me this afternoon about Steve Bennetts Sierra when it backfired on gas ! slight curse there possibly

I would say its time for a set of direct port injectors really, cant really trust that manifold to flow the nitrous equally and its maybe a slightly expensive engine to be taking any more risks with,

fair play though, I'm sure chip will be on here later to give a good solution to fixing the problem if its caused by nitrous