Hi
With N/A engines it is harder to extract more performance.
But there are a few things you could consider.
Yes there is the engine conversion.
We have not long since completed a 1.8T conversion in to a 6N Polo
This was lovely and it had a turbo conversion too.
But if you are going to the extent of this what you have to realise is that the ECU should be used from the donor vehicle.
This requires the whiole of the engine bay to be rewired.
The clutch goes to hydraulic and the cable removed on the accelerator to be replaced by a sensor.
Mmmm not easy.
Then you could always look at Nitros?
We do this and I do believe that Josh had his Polo with Nitos on.
We use a set up that is road legal in this country and the system is progressive.
You dont hit the red button and get thrown back in the seat like you see at the pictures.
This uses a sensor on the accelerator and adjusts to suit.
I would think for your needs that this could just suit.
With remaps as has been discussed we could always offer you Custom-Code.
www.custom-code.co.uk is the web site.
If I can help you further please feel free to give me a call.
My number is 01246 455005
Hope this has helped you slightly , if not call me and I can help you more
Sarah