Well, all the this just proves how fickle insurance premiums can be. I take my hat off to you both, Nonamecc79 and Beanus. I couldn’t afford to get cover at those prices, your determination to continue on with those premiums is fantastic dedication to the GTO. I hope you both soon are rewarded with lower premiums.
Not to labour the point too much, percentage increase or decrease is best calculated as:-
DIFFERENCE (between factory and modified power), DIVIDED BY FACTORY POWER, multiplied by 100.
So, if the car had a factory production power output of 320bhp, and was eventually modified to 430bhp…
= 110, multiplied by 100, then divided by 320 = 34 and a bit %
Mike