I have a Skoda Octavia 5 1.6 MPI and I want to make a good cheap safe tuning that will increase the cars performance above 100 hp it already has. How can I do that?
The Octavia has the same 1.6 MPI engine as in the Volkswagens so, technically, pretty much all the tuning options available to them are available to you. Given the 10.5:1 compression ratio, however, I would recommend that you keep your expectations low. There isn't a lot of room for the casual tuner.
The vendors that I've found generally cite an increase of 10% to power and torque, resulting in a drop from 12 to 11 seconds for 0-100 kph. Those are marketing numbers, though, so caveat emptor.
You might have more luck with the standard replacement of intake, header and exhaust. If you pick the right gear, you should see a performance bump combined with a weight decrease. Also, once your engine has better air flow it might be able to combine those changes, high quality fuel and a more aggressive tune to give you a more impressive power improvement.