Yeah you need a bigger map sensor and you also need an outlet for the the charger. I had a g60 charger and outlet then scrapped the idea as the charger will just kill the gearbox.
I had a 120 degree one i think, thats what you really need but there expensive.
By the time you have brought a charger (serviced or unserviced, ported or un-ported), air inlet adapter, charger bracket, pulleys, outlet, some custom pipework, map sensor, possibly 310cc injectors, it wont be far off going turbo. My charger i got was quite cheap but it needed porting and servicing. Thats easily £400 on them 2 bits so its best to get a charger thats been recently serviced and ported. Most of the time i see then go on ebay for £500+.
Just get a G60/G65 or G75 charger
this is what djtez has roughly priced up on going g60 but not everything is on the list
£380 G60 supercharger stage 4 (rebuilt by g-werks)
£435 Jabbasport rebuild (spoke to Brian but no idea about the high rpms)
£71 G60 bracket to fit G40 engine (tensioner)
£29 Toothed Belt to fit
£46 Toothed pulley to fit G60 (70mm?)
£66 G60 race inlet 90mm
£49 G60 Rs outlet
Engine Parts
£550 Wossner Piston 77mm
£150 Engine Rebore of 2mm
£120 crank regrind (if required)
Fueling
£95 Bosch 315cc, 14.5ohm (reconditioned)
£60 Sytec FSE In-line Fuel pump (otp017)
Managment
£33 250kpa 1.5 bar limit MAP sensor
£??? When i find someone to give me a map!
Extras.!
£70 Universal Front mount
£100 Intercooler piping
£??? Labour on Agra Engineering rebuilt bottom end.(£45/hr)
There is a polo G60 on a german forum that is claiming to have 241bhp running 65mm pulley and 1.6bar of boost.