The conversions are making more HP at the moment, the A-series turbos are making awesome power from an A series.
It all depends, a turbo setup done properly you are looking at around $5k with head work, etc etc (prolly a bit high) with the conversion its alot more and its no longer a Mini engine.
You can fit a turbo setup onto your A series without body mods, its the exhaust manifold that is the problem... depending on the size of the turbo, you CAN fit behind the engine also without mods but its a much tighter setup.
Ill stick to A series turbo, its the challenge of beating the conversions for me
A mate of mine has a Honda CRX weighing the same as a mini, turbo B16A motor, makes 560hp at the front wheels. I dont ever see an A series making that same power.
A mini turbo'd imho is still a mini - soon as you replace it completely with a conversion it takes away the mini classic A series for me... would I do a conversion though? Yeh for sure, not for a road car, but a drag or race car for fun only.
Peter.