the problem with opel engines is that the tensile strength of the pistons can not withstand forced induction (turbo or supercharged). In germany, they replace stock pistons with forged pistons and re-calibrate it to lower compression ratio.
And you said you wanted it to go faster. What would you like to achieve? Or what is your objective for making it fast? Just a bit faster for street use? How far do you want to go? How much is your budget?
The most basic would be your first step: K&N filter, then replace your headers to 4-2-1 or 4-1 depending on how you're gonna use it, and a better flowing exhaust.
After that, it's more a matter of purpose and money.