My insurance company (adrian flux) bases increases on a %age.
So if power std was 197bhp (GTI) and goes upto 235bhp (Average) your current premium would increase by 19% along with getting a 19% power hike, so if you currently pay £500 a year expect a £100 increase on stage 1.
I already spoke to my ins co about mods and the figures they gave me were
Stg 1 is a 32% increase in premium, although she told me i can have an air filter and uprated exhaust and it wont affect premium as long as its stage 1 re-map, so what she was saying is if i have the wrong map on for mods i have they wont increase further
Stg 2 is a 49% increase in premium
So for me my ED30 stg 1 premium would be £616, and stage 2 would be £695! (another £80 for 40bhp
)
If i went stg 1 then stage my premium would actually end up being £720 (They charge on current policy price, crafty buggers!)