A modified, small engined car will be more expensive to insure than a standard larger engine one.

If it were me, keep your car standard and tidy for the first few years while you build up a bit of no claims, then when you can afford to insure something decent, either start modifying what you already have, or sell it and buy something quick out of the box.

If I hadn't wasted so much cash on crap cars when I was younger I would have an awesome car by now lol