so i have a cat back system now buit i want a catless midpipe. if i just install it as is i would get a cel correct? so how would i go about clearing the CEL and being able to run the midpipe without a CEL?

put electrical tape over it. Or search the forums for an accessport or spark plug spacer.

Yes you will get a CEL.
The Cobb AccessPort (using a MazdaManiac map) will mask emmissions cel's ($695).
There are "MIL Eliminators" for sale all over the Interwebs (or you can make your own from Radio Shack). What they do is use a capacitor and resistor (replacing the Rear O2 sensor) to provide a steady voltage to fool the computer. From what I've read here, they are not very successful on the RX-8. The problem seems to be that the ECU expects different voltages as the car warms up - and throws a code if the voltage is constant.

yes def a CEL the only way i know is like above is get the accessport

put electrical tape over it. Or search the forums for an accessport or spark plug spacer.

what would the spark plug spacer do?

A spark plug spacer is an extension that moves the rear O2 sensor out of the flow of exhaust gasses.

Note that our rear O2 sensor is a device that transmits varying voltage to the ECU based on the oxygen content of the exhaust stream. If you move the sensor the *right* distance, then it will transfer different voltages from its normal location. It's getting this distance *right* that is the challenge.

i installed a midpipe on mine this weekend...NO cel

you just wait.

I had a midpipe on for quite sometime and never got a CEL. It was the Agency Power midpipe. I took it off because it was insane loud.

i installed a midpipe on mine this weekend...NO cel

Give it a few drive cycles. Mine lasted a couple days without a CEL (both the AP and MazSport midpipe).
But few were lucky and never received one.

Well there you.. isane loud and ticket or Cel.

'04s often don't get CAT efficiency CELs.