I spent some time thinking about sizing the turbocharger for the project. I have been reading the turbocharging performance handbook by Jeff Hartman.

https://www.amazon.co.uk/Turbocharging-Performance-Handbook-Motorbooks-Workshop/dp/0760328056/ref=sr_1_1?s=books&ie=UTF8&qid=1489498362&sr=1-1&keywords=turbocharging

Using this i have determined that to get a peak power of 250hp at 7750RPM i will need 7.2 PSI at the engine inlet which equates to around 9PSI across the compressor (including losses in the pipework, air filter etc). This is at a flow rate of 12.47 kg/minute.

I was then able to look at compressor graphs for various turbo chargers. Is seems that turbo charger compressors are optimised for higher boost pressures so there were not many that seemed to suit my application. Did a bit of ebay browsing and Mitsubishi TD04 turbos originally fitted to SAAB 9-3's seemed to be the best match. I put an £85 pound offer on a used example and the seller accepted. Should receive it in the next few days.