Have been researching this a lot and the most recommended way to improve power is to upgrade to a 1.3 litre engine
Turbo is not recommended, apart from poor reliability, it consists of a difficult job
If you pop in a 1.3 engine, you can outbore the block which increases the cc but yoo'll need an expert to do this, and if you find one, let me know
The next thing would be to place a stage 1 kit which costs around 165 pounds. Its a new manifold and a free flow exhaust. Bare in mind any exhaust thats bigger than 2" on a mini then you'll loose power. The stage one kit also includes a new needle for a richer flow, which tal mentioned earlier
majority of feedback would indicate that a stage one set kit would give you around 12% or more extra power
I am running off what i approx at 38bhp, with a 1.3 engine and stage one, that should take me nearer 70bhp
There are endless things you can do to make it faster and stronger, but its just a matter of how many shekals you wanna spend, hence the best and most cost effective method is engine upgrade and stage one
I am saving up for my new engine