There are some good noises to listen to on youtube - there are links on the video section of this site.
Also check out spyderchat.com
They have loads of engine swap info there (based mainly in the US) People have even put the new honda K20 engine in there.
Celica engine swaps seem to be the most common (like the one in the newer UK elises) and then all sorts of madness can be done to that.
Personally, while I'm being swayed by some to do engine mods... thanks funexec... I want to be going slow enough to be seen
If anyone wants to race, just laugh and turn up the tunes!!!!
In the US you can pick up a turbo for $4k. This will get you well onto the way to 200bhp (though not quite there)
0-60 in 7 seconds isn't exactly slow on the standard car so youre never going to be embarrased (unlike some of the VW beetle lambo kits of the 80's!!!)