It's a joke doing it online. As soon as you tick the "non standard engine" box it goes mental with the price.
Don't really get it seeing as a bored out engine or remap with more power percentage increase doesn't seem to affect the premium compared to standard. ( I ticked different boxes out of curiosity )
Most online insurers are set up for standard UK car insurance, it is almost impossible to have an accurate online quotation tool for this type of specialist car insurance.