Update:
Took the long trip to Random today, and ended up spending the better part of the day there. I tripped my CEL after 600 miles of driving, and after resetting the ECU, again after 60 miles. The test pipe with cat was removed at random, and the cat had melted on the outside of the substrate. It had melted enough to allow the converter to move around inside its housing. Dave was VERY surprised, and asserted that he had never seen this happen in a N/A car. The area around the cat had blued quite a bit, which is a sign of excess heat. So, new prototype, this time using a 5" diameter cat rather than a 4". Hopefully this will give more surface area for the cat to cool and keep temps at check. My CEL had tripped because some of the catalyst had already been burned off and the converter efficiency was not what it was suppossed to be. I will run this cat for a while and see how it performs. It is not an everyday part, and was rather cut out of test setup.
Other options were discussed, including moving the cat to the end of the midpipe and extending the lines to the O2 sensor. Time will only tell if these have to be implemented.
Obviously the rotary motor puts out lots of heat, even though Dave said he had never seen this happen in an RX7. I drive the car like it should be, try to never shoot flames, and put alot of HW miles, so I do not believe I was abusing the Cat horribly. Now the question is: How is Maurice using this setup without a hitch? Does the ECU Stage 1 mod actually lower AVERAGE temps by reducing the amount of unburned fuel entering the cat? We shall see...

 

Thanks for the update. Sounds like more time is needed to work out the details.

Make sure to keep us posted.

 

Generally, when one leans out the mixture of fuel, the exhaust gets hotter. Mazda made our mixture rich in the first place for cooler exhaust gases. It is indeed odd that Maurice is still running his random cat and yours has melted. One possibility may simply be that Maurice hasn't been driving much because of the cold temperatures in Canada, but only he knows that for sure.

 

Xavier, let me get this straight: You have the stage I and a Random Tech Cat melted from that setup? That seems weird. I mean, I thought Random Tech's cats were supposed to withstand more punishment than stock? How can our stock cats hold up so well if an aftermarket one doesn't cut it?

 

I am NOT running stage I, I hope it arrives soon. So on a stock car I have melted the 4" random cat in about 500 miles. No one has been able to explain it. It has been postulated that the small random cat cannot dispell excess heat like the giant stock cat. The stock cat is at least 6" in diameter and 3 times longer than the random cat. This gives it a large amount of surface area to handle all of the heat generated by the Renesis. My midpipe section was VERY blue around the random cat, demonstrating how hot that area had been. When an exhaust pipe overheats, the color of the pipe gets a slight blue tint to it. Half of my pipe looked like this.
As of now I am running a 5" prototype random cat, trying to take the same course at the stocker buy greatly increasing the surface area that the exhaust gases meet. A 5" cat is 50% larger in its cross section than a 4" cat. Now all I can do is drive the car normally and see what this cat does.
All I know is: I melted a cat, Maurice has not. What's different, I'm not sure. I just hope others who install these cats on their cars don't have the same problems I have. The only 2 variables that are different that I know of are the Borla and the chip tuning. I have a Borla, he has chip tuning. hehe.

 

Maybe the extra rich stock fuel maps are to blame. It would be interesting to see the exhaust gas temps just after the cat on your car versus another with the Random Tech and Stage 1. If all of that extra fuel is igniting in the cat your exhaust temps are going to go through the roof!

 

It's funny you should say that. I know that Mazda supposedly richened the mixture to cool the cat temps, but it doesn't make sense to me how. Less efficient burn?

My first car was an '89 Mazda 323. I screwed up the spark plug wiring one day and the end result was a car that ran on two cylinders for about 20 miles before I made it to a mechanic...Yeah, I was a dumb-*** for not figuring out what I messed up on. Anyway, all that unburnt fuel made that cat glow cherry red during my little trip. How hot was it? Well, my carpet inside my car was smoking.

Surprisingly, the cat survived, but that's why it doesn't make sense to me why a richened mixture lowers cat temps

 

It sounds like Mazda has gone way beyond rich and is bordering on just plain drowning the engine. I believe that Rotary God said that if there was not enough O2 present in the exhaust the gas would not be physically able to ignite completely while passing through the cat and thus cool it off.

With your new cat, the flow dynamics have changed and it may be creating a situation where the gas is now able to ignite and thus drive up the temps. This would also make sense because the same Random Tech cat has been used successfully with the leaner Canzoomer Stage 2 ECU (leaner = lower EGT).

 

It isn't that rich. The A/F ratio is in the 11:1 range (very rich) but only at WOT.
At lesser throttle positions (mostly 50% to 70%) the A/F is closer to 12.5:1.
Optimal (in my estimation) is about 13.7:1 and I tune to 13.5:1 for a margin of safety.
Drowning the motor would be more like 10:1 which is what the STI does. Amazing that it runs, but every motor is different.
I think 9:1 is where there isn't enough O2 for combustion at all.

BTW, leaner A/F = higher EGT. I imagine that was just a typo on your part.
Advancing the timing will reduce EGT to some degree also, despite what I have seen written from time to time around here.
Retarded ignition timing raises EGT.

 

I made a trip to Random yesterday and had the stock converter put back on. I need to take the car in for an oil change, recalls, and ECU reflash. While I did throw a CEL with the 5" cat, it looked perfect when we removed it, unlike the extremely blued and destroyed 4" cat. Maybe this will be a more permanent setup, and the answer for other RX8 owners.

 

So where in the process are you now?....i will be heading up to Suwanee during the next few weeks and would like to drop by and see your setup if you have been back to RT to test more...

 

Yeah, I'd like to know this too. And maybe you could throw a pic or two of the new cat up?