insurance companies have there own littel methods.
it appears the risk is worked out in various ares them its all added up. i for the car
eg:
value
de denting cost.
nickablity
hedge seeking skills
so really bigga motor only slightly increases hedge seeking skills of the car and the % increase of power seems to affect the cost of that part of the price pritty much 1 for 1.
so you gives it 100% more power the part of the program that looks up your cars hedge seeking skills takes the std number and applys said factor ( 100% extra ) but as de denting and nickablity and shizzel won't have really changed it dosent doubel the policy.
also soem insurers apply logic, and must look at what you've crashed , not crashed. also converting a car you've owned for over a year give much less steep quote that buying one.
ive allways found it with the quicker cars ive had, 1st quote quite steep but after sucsessfully avoided hedges for the year theres a massive differance last quote for my gold was same price as a std one

so am workign on fitting more hedgeseeking to it