same as ever it's not the actual engine (which of course will cost a fortune) but all the ancillaries that'll add up - fuel system, suspension, brakes, diffs, management, gearbox, gauges, etc - a 650bhp car is a fucking weapon, it's no good just banging a massive lump into a car that's not built for it or at best it'll be constantly breaking, at worst you'll hurt yourself & others.