Adrian Flux are very very good for modified cars. I am 36 with 7yrs NCB but live in a bad postcode so pretty much fucked whatever I drive. Adrian Flux gave me the best price for my Audi TT 225bhp, it's completely standard, but the specialist policy has a modifications clause, I can do ANY modification to my car, and it is a flat rate increase of about £25 or so, and that covers ALL modifications, worth thinking about. The compare sites are utterly shit for anything performance or modified, you need to use specialists.
Also try Lancaster Insurance. And there are a couple of others but I've not used them as they don't cover certain bad postcodes.