how to upgrade RX-8 engine??

Try rx8club.com or one of the sites that is dedicated to these great cars.

The one accessory a RX8 car must have is a driver who has read the owners manual and will follow the right start routine every time!

One thing Mazda has never been able to do-

Sell RX cars only to those smart enough to own one.

I hate to tell you but the RX8 is a failed experiment. I am astonished that it has achieved such a mileage unless the engine was rebuilt or exchanged. They look good, drive well but drink fuel and oil and are very unreliable. Sorry for the bad news but I thought you should know. All you can do is use fully synthetic oil and keep your fingers crossed.