Is a high flow cat needed for a boosted RX-8? I am thinking of keeping my stock cat but I am worried that its going to fail.

Does anyone have a stock cat with their greddy turbo and not have any problems?

Its not needed but its helpful. The less back pressure for a turbo, the better. Your stock cat will definitely have a shorter lifetime though.

Get rid of it all together.

Go straight man, i mean the pipe

As far as cat life goes, the turbo is actually an effective heatsink so less heat will get to it until you are on it really hard and that isn't all that much in terms of total time with the vehicle running unless you are racing it constantly.

The cat poses a restriction in the exhaust. On a turbo car no exhaust after the turbo is the best response. There are some that will claim that backpressure is needed to help the turbo spool and make low end but this is false. By getting rid of it you will free up some power and will increase the spool rate of the turbo. Be careful about tuning though. As a general rule for every psi of backpressure you free up on a turbo car, it is equivalent of giving yourself 2 psi of boost. This isn't a set in stone number but the point is the same nevertheless. If you are using a state of tune that was designed for a cat, it will be incorrectly tuned without one and you risk engine damage from an improper tune. I suspect we've already seen that in a few turbo'd RX-8's and just haven't had all the details.

You'll find that without a cat, you will make more power and have greater response (less lag) than with it. Even at the same boost level. This assumes you get it retuned. Don't be tempted to go without this step. Getting it tuned and paying for it if you can't do it is still faster and easier than waiting and paying for an engine rebuild. You could even do a larger exhaust with a turbo system than with a nonturbo as backpressure is all we are concerned about, or more accurately reducing it. We aren't also looking for exhaust velocity as on a nonturbo car. This is the only time when a bigger exhaust is better. (There is a point of diminishing returns though.)

If you can, free up the exhaust and get it retuned. You'll love it.

I have the stock cat on mine for over a year with the turbo and no problems yet.

i also have been running on the stock cat for some time - and it hasn't melted or exploded either... heh heh! i'd go with the complete TurboXs system right now, if they widened out the tips or at a minimum, extend them by another 2-3". is there another turbo friendly (full 3") exhaust system on the market?

dd sends...

Isnt the new mazdaspeed dual exhaust good for the turbo?

My CaT failed after about 8K miles ~ I just reset my CEL. and "waiting" for it to come back on so I can bring it to my dealer to fix it hehehe