you can, but getting it past inspection might be hard. We allow 10% power improvement without recertification, but with approval. Any more and you'd be up for engineers signing of on the engine change, and all the other upgrades needed to go with it. VERY expensive. Cheaper to buy other car usually. Put up with it until it's paid for, and then you can get something else. Do NOT sell/trade it away if you have only bought it recently and its on Hire Purchase. You will loose $$$ very badly. Perhaps, by the time it's paid for, you'll be less of a petrol head, and a bit wiser as to what you really need, and can handle.