Hi mate. Lift the bonnet and you'll have a black inlet manifold with states 'VVC' on it. That's the 160.
In terms of performance, there is a lot you could do.
If you have the 120 model, you could buy a decent enclosed induction kit, a 4-2-1 exhaust manifold, a sports cat and a decent exhaust. Also you can head to a breakers or search eBay for MGTF 135 cam shafts.
Combine what I've said plus a remap from Z&F and you'll get around 140bhp.
The VVC models are a little more complicated due to the VVC mechanism. VVC is good for about 190bhp. Then you need to consider a blanking kit and solid cams if you want more power and possibly throttle bodies.
To squeeze 190bhp out the VVC you need to do the following (Deep pockets are needed)
Ported and polished + Gas flowed head
Paul Ivey 3 angle cut valves and seats (I think that's the term used)
Piper 270 profile exhaust cam with Vernier pullies
Janspeed exhaust system
ITG Maxogen induction kit
Remap.
You can also use throttle bodies on the 120 and 160 with very good gains, but it's costly.
In regards to gearboxes, the VVC model uses a PG1 box which the T16 boys run and are good for 300bhp.
The 120 also uses a PG1 but with longer 5 gear.
If you want an all round package, try going to ptp performance, they do clutches, flywheels etc etc
Now, most people don't both tuning the any of the NA lumps... Instead they whack a turbo engine in.
You can either do a T16 conversion in which you'll need either of the following as it makes life easier:
220 turbo coupe
420 turbo
620 turbo
If you can find a doner car, you'll be laughing...
Or if all that work doesn't interest you there is always either the 1.8K series turbo engine found in the MG ZT or you could a buy an early wet liner 1.4 k series engine and turbo that. 200bhp is easily attainable.