Wow you get all the best stereotypical myths on the Internet.
Firstly American tuning is in no way as prehistroic as people think, they just have different fundementals behind what they consider performance. The small block Chevy is just the American equivilent of our Pinto, it's old popular technology but doesn't not represent the cream of the crop. The comments about petrol consumption and American v8's make me laugh, how many people actually think a 500bhp 2.0 turbo uses less fuel then a 500bhp v8? Laws of thermodynamics anybody? The recent American V8s get just as much power per litre than our fourpots and with fuel injection are just as effcient.
Everyone rants on about the Japanese tuning market, consider this. It costs tens of thousands to get 1000bhp from a Skyline engine, it will be laggy and generally hard to drive. For a tenth of that price you can buy a brand new big block V8 and a supercharger and have 1000bhp in a more drivable form. It wont be using anymore fuel and will be a lot more reliable. Spend a little more and you go for Aluminium block, heads and intake and be laughing as it will weigh no more than the 6pot and hairdryers.
Also lets not forget the real ace in the pack, the Rover V8. Weighs less than a Minis A-series lump and can be made to give huge power on a cheap budget.