Flow figures:



The head compares well to the S14 Evo head (see
Link), but it would be unwise to compare the figures for the M42 and S14 Evo too closely - different flow testing machine, different temperature, etc.
The head porter said if everything was optimised, cams, compression, extractors, fuel, etc, the head would be good for about 280hp or so. There is no way I'd be able to achieve anything like this. Lack of the readies $$$$.
He also said the standard M42 is quite good ... similar to other stock 2 litre 16v heads he's played with (mostly Nissan), which is notable given that it's on a 1.8 litre.