Exhaust back box change - need to declare to insurer?

[Garry1127]

Hello all,

I am in the future considering changing the back box on my Jaguar 5.0 XK from the standard twin exhaust to a quad exhaust, primarily for looks and sound but there could be a power increase of up to 20hp.

I think this means that I will need to declare it to my insurance company, has anyone done this? and what impact did this declaration have on their premium?

Thanks