There aren't many production engines that sound better at full song than BMW's V-10, which manages to simply scream rather than sounding like a truck as many other V-10s do (we're looking at you, Viper). But putting one in a 1996 Subaru WRX? That doesn't sound so great.
That is, it doesn't sound so great until you see it in action. Sure, the engine is probably worth twice what the car is, but who cares: it looks like the fun is worth five times the price of the engine.