I'm looking at putting a high power engine 6port engine in my 4portRX8.
How much does this engine cost? And which other parts do I have to change?

 

Considering the scope of what you'd need, I'd reccomend trading in for another 8. Otherwise, you'll need an entire car (wrecked) to do this and if you count your time would probably have more in it than a new car costs.

Not sure if you'd need a new transmission (although you'd definately want one), but if I remember correctly there are computer and wiring differences between the two Renesis engines, which means you need the 6 port computer and associated electronics.

 

And don't forget warranty. Seriously, trading in for a 6 speed 8 is much cheaper. That's what I plan on doing.