My original 98,000 miles Mazda cats.
My 40,000 Bonez - started being too stinky after around 30,000 miles.
My brand new RX7 store cat.

Observations: the best cat of course is the factory. The Bonez has a real nice tone once you are above 4000 and both turbos are running.
The Bonez also looks more robust than the RX7 Store cat.

The RX7 store cat is the loudest of them all.

 

Here is the inside of a Mazda cat with only 10,000 miles

 

Nice toy

 

 

Thanks. Besides looking inside engine and cats, I use it for cut-rate colonoscopy.

 

BTW - that motor I got from you is still running strong, even after I had JB-Welded the oil pan bolt holes together. No leaks even with Running 14psi with water injection. Water Injection is the best thing next to 110 octane gas.

 

Glad to hear it.

 

What you are seeing there, that 100k degradation, is definitely the result of a lot of heat. 20 years ago when these cars came out, emission standards were not nearly as tight and cats weren't required to last so long.

 

You should list the difference in weight between all of them

 

OEM Cat weighed 31 lbs.
Bonez Cat weighed 14 lbs.
RX7Store weighed 13 lbs.
Midpipe weighed 9 lbs.

The RX7 store pipe is really loud when I'm above 6000 rpm; not that I mind but I was surprised at how loud it was.

Because my motor is streetported, it's still not perfectly clean but that was better than the worn out Bonez. It was so bad, I had to turn off my engine at stoplight.

I'm debating running two Magnaflo cats in parallel for an even cleaner exhaust.

 

I was about to post a thread ask about something similar. Dont mind me if I hi-jack this thread.

Question is, I am looking forward to have my car tuned @ 450-500hp. I live in CA and I wanted it somewhat quiet yet flows well.

Do you guys suggest a Bonez Hi-flow? or can I weld two magnaflo cats in there? Please advise.

-AzEKnightz

 

There is a lot of precious metals in these big cats. Something like 1-3 oz of platinum (at $1700 per troy ounce), 0.5 oz of palladium and even smaller amount of rhodium.

That is why people are stealing these cats, especially the big ones in the SUVs and Mercedes.

 

This would be interesting to see

 

Just a bit of caution on the Magnaflow cats. I tried one of the metal substrate ones on my 3 rotor and it lasted all of about 200 miles. Completely burnt out the insides into a nice little ball. And this was with the cat installed at the end of the midpipe to try to avoid some heat.

The sales guys at Magnaflow will tell you that their cats will work no problems with rotary EGTs and airflow but this obviously isn't the case. My EGTs run around 1,100 - 1,200 at cruise so not very hot compared to a lot of other rotaries and I don't think I've every seen anything above 1,250 that I can recall. The techie guys will tell you something else, that their cats won't work on rotaries. Wish I knew that before purchasing.

Having said that, I'd wager part of my problem was too much airflow thru the one cat so I've got a new plan (taken from rotor motor) and matching pomanferrari's idea of installing two of the Magnaflow cats in parallel. Going to split from the 3 inch downpipe into two 2.5 inch pipes, with each one feeding a cat. After the cats, I'll reverse it back to the 3 inch tailpipe. In theory, this will cut the airflow in half for each cat, with the hope that the cats can take the heat and airflow. As I would be moving the cats forward from what I've got now with the one cat, that concerns me with the heat but you don't know until you try it.

Here is the one I previously tried:

 

If you're running rich, you might just end up burning them out again in short order.

I've been running two 3" ID x 4" OD metal core magnaflow cats (59929) on my ~520hp LS2 FD, and I've put about 6k miles on them, including Texas Mile runs ~2k miles ago. No problems so far, but now I'll definitely keep an eye on them... I don't expect them to last forever, but 200 miles is ridiculous! I have to think something else is up...

 

Had a really good tune on the car with idle at around 12.8, cruise at 13.8 and WOT at 11.5 so who knows. I think I'll try the two cats in parallel idea and see what happens.

Do you run yours in series or parallel?

 

Do you have an air pump? Or the switching valve under the intake manifold? Your AFRs would suggest no emissions devices. If you do not have them there is no point to run a cat. The stock FD emissions devices greatly dilute the exhaust both up and downstream of the cat. This greatly reduces emissions and your cat will last a lot longer.

Tri-Point sells a 3" magnaflow 50state CARB legal cat that is complete with air pipe. No need to cut the old one off.

EB Turbo

 

Run them in PARALLEL, definitely. Less flow restriction, and each cat sees only half the flow, half the unburned fuel. Like with resistors, 2 in parallel is 1/4 the resistance/restriction as 2 in series.

 

Air pump? I don't need no stinking air pump No, none of that on my 3 rotor. I need a cat for two reasons: 1) to participate in the Modified Magazine Tuner Shootout. I'm going to attend next year and one of the requirements is to have a functional cat on the car and 2) to cut down on the stink as much as possible. For the short time the cat worked, the smell went way down and I wouldn't mind that again.

Okay, thanks. I think that is the way to go. Do you have pics of how you fit them under the car? I've been thinking thru how to do this and make everything fit.

 

Mine being a V8, it's a bit easier. Don't know if this will help you with a 3-rotor, but here are pics:

 

Thanks. That is different and I will need to come up with something else. Have been thinking the best route is to stagger the cats with one positioned in front of the other. So, coming off the downpipe, split the flow there, and then thread thru the two 2.5 inch pipes by installing one cat and routing the piping for the other next to it back to the second cat, and reversing this for the second cat, with it all coming back together before the tailpipe.

We shall see.

 

If you do not need to pass emissions testing you should put a 3.5" - 4" metal substraight. The car will not even come close to passing out of the tailpipe but that is not your concern.

EB Turbo

 

Possibly dumb idea here: run single nearly all the way back, then split and run two short 4" OD cats in place of muffler? Just thinking out loud, I know that cats want to be closer to the engine to get hot enough to light off, but might meet your needs...

 

Might want to consider a Random Technology metal cat. It is pretty compact so easy to fit in tight spots. I ran one for a few years before I got my SMB mid pipe. Look for my old posts on metal cats.

 

Wow, I did not think that 100k cats look that bad inside. So my cat, having 100k probably looks about the same huh? Question is, how will this effect emissions?
I need to pass smog real soon, how will a 100k cat do on smog? Could I fail because of it?
Also, if those bricks are broken down like that, does that restrict the exhaust flow pretty bad?