What's the worse it can happen? Blown engine? You can get a SH engine for 370z for £3k, is not the end of the world.
In reality, I'll give you just one example. Charles, the owner of CJM in USA, had exactly the same car and same kit as me, ran it for over 60.000 miles with no problems at all. Took the kit off recently and sold it on the forum. '09 370z, Twin Turbo, E85. 671rwhp @ 12 psi - STOCK ENGINE!! 11.2 @ 133mph