Only way to get good performance upgrades on the RX8 is FI (forced induction).
The RX8 was engineered VERY well and its difficult to gain much more HP without FI.
Popular FI options are:
- Pettit's Supercharger
- Esmeril's Turbo
- Greddy Turbo (find a cheap used kit then get the MazdaManiac upgrade)
There are others, but these are the popular kits within the RX8 community.
BHR (Black Halo Racing along with MazdaManiac) will be introducing a turbo kit possibly within the year.
Do some MAJOR researching before going this route and don't go with a kit that shows the most peak (keyword is peak) horse power.
The Esmeril can do 414HP at 16PSI... but you really don't want that with a street car. They produce 366HP at 13PSI which is more tolerable on the streets.
Now if FI isn't for you just yet, the only N/A upgrades that'll give you some performance is:
- Mid-pipe (high flow or cat delete)
- Cobb AccessPort (allows you to tweak the tuning)
- Ignition coil upgrade (BHR just released a GM Yukon coil conversion) and this is because the stock coils are weak and prone to failure
- Lighter flywheel and short-shifter (maybe not much HP performance, but noticeable while accelerating)
- Wheels and suspension upgrade (no matter how much power you can produce, you still need to transfer that power to the road)
People will argue to get a CAI (cold air intake) system. Many don't realize that the stock RX8 has a CAI system when you consider the VFAD assembly in the front.
I've had the AEM and Racing Beat CAI setup and there isn't much gain at all (not enough that your "butt" dyno can tell).
Both systems will give you a nice deep sound, so don't spend the cash and expect a large boost.