Incidentally the 3 exhaust ports on the OBX header are 49.5mm x 27.5mm

 

I wish now I had measured the stock manifold before putting it back on for comparison.

 

I already measured the stock header from my car. The 2 outside ports measure 53mm x 36.8 and the centre port measures 53 x 23.8. There will be a small variation between stock headers as they are mass produced, but those measurements are good enough for comparison purposes.
It appears that the stock headers 2 outside ports are way oversized for some reason?

 

are you guys sure that the obx headers with holes to hold air injection has actually notch ine the big hole to gives air to the other? because i have them on my car, the dealer installed them for me and installed the air injection hole, but the big hole was all dark and we didnt pay atention to these notches in the hole.... so they just disconnected the air pump in the engine bay! i do have this p0411 code running and am running some problem right now....

see this post; https://www.rx8club.com/series-i-trouble-shooting-95/weird-power-loss-intermittent-186974/

 

Hey guys, Mazurfer pointed me to this thread because i am also experiencing the P0411 code.
I have ran with an AEM CAI and Borla CATback for 6 months, no issues. I had mazda install my new Racing Beat Header on 11-26-09, and i retained my stock Converter. My CEL appeared about 100 miles after the install. Mazda was nice enough to find the code for me and clear it for free. They said if it comes back they'll investigate more. So i drove home with no CEL, however the next time i started my car it lit up again. i thought maybe the air/fuel ratio didnt adjust correctly? i could be very wrong, but im just looking for help. Also this may be all in my head, but it actually feels like i have lost some power..

 

let me know what you find installed my racing beat header experiencing the same problem have no idea what it is.

 

Dealing with this myself on my 09 with a RB header. I was told to make sure the gasket is straight and the tube is on tight. I unfortunately stripped one of the fasteners and so will be taking it to a mechanic for some help. Hopefully its something simple.

 

I own an 2008 RX8 auto. I installed the racing beat headers and exhaust kit in September 2014. I received the code after the second cold start. I have checked all connecting wires, hoses, and etc. I am thinkng about adding another secondary air pump to increase the air flow over and through the exhaust mixture. Since the headers are larger I am assuming that it needs more air flow to fill in the additional volume in the headers.

Did you come up with and solution?