Matt Hey

Interesting. Logic dictates 2 possible conclusions...

1. test RX-7 has problems
2. Random metal cat is crap

I think I'll stay away from the Random cats especially considering there are less expensive alternatives on the market. I wish I knew which companies manufactured which cats.

David Beale

Don't jump to conclusions. It's a delicate balance act to design a cat for each car. You have to get the cat hot quickly so as to burn right after startup, but not too hot so it doesn't destroy itself on the highway. The 4" was ok on the RX-8 until owners started driving hard. Then they started overheating the cat. The worst thing for the cat is excess fuel. On the RX-8 Mazda were injecting excess fuel to get the cat to heat up - this may be what made the 4" fail. The 5" is just fine. Same goes for the RX-7 - that is the car I mentioned with the Pettit ECU was probably injecting too much fuel (for safety). I suspect that is what caused his cats to fail. Mine runs a little lean - not lean enough to detonate, but I get pretty good mileage and never see soot out the exhaust. Running boost higher than stock (10 PSI) will also add more energy to the exhaust.
As for an RX-7 generating more heat than an RX-8, think about that statement for a minute - the RX-7 extracts heat from the exhaust with the turbos. If you make the measurements you'll find the exhaust temp on the RX-8 is actually higher. I think excess fuel was what was damaging the cats.
The RX-7 will actually burn some of the excess fuel in the turbos, so again the RX-8 should be harder on cats than the RX-7.
I actually get better mileage than my friend in his RX-8 - which causes him great consternation.

rebuild FD

exactly, which is why any cat in an FD will be short lived, especially a high boost FD running AFRs of about 11.8 (or less) for safety

NO cat can handle that for long

rebuild FD

at high boost the RX-7 is burning ALOT more fuel that an RX-8....the extra heat of combustion has to go somewhere

bone stock you may be right (maybe), but 15 psi, 17 psi, 350-400 hp? no way

rebuild FD

??

Matt Hey

I agree that NA cars have higher EGT temps. I have an NA RX-7 with a Bonez (ceramic) cat that has lasted for years. I have an extremally rich '93 RX-7 with stock twin turbos (10-12 psi) that has an N-Tech (ceramic) cat that has lasted over a year. The Random metal cats don't seem to last very long though? It would help if people chimed in about how they have been running them with no problems on a rotary. With cheaper alternatives on the market I think I will stear clear of the Random metal cat. I appreciate the continued testing of all the metal cats. I hope at some point we know some reliable, high performance, quieter, less stinky, and reasonably priced metal cats that rotary owners can choose instead of mid pipes or resonated mid pipes.

The FD does everything it can to heat the cats up on startup as well. It has the AWS which idles higher and injects air into the exhaust. It may also retard timing substantially when cold to warm up the cat. The PFC is very retarded when cold and advancing it with the Datalogit makes the car much smoother.

MichaelFregoe

iTrader: (1)

What is the latest on this... What is the alternative other than a random metallic cat? The thread has bounced around so much it is difficult to follow. Summary?

MichaelFregoe

iTrader: (1)

I just spoke to Canzoomer and they are selling an FD Mid-pipe with a 5 inch metallic catalytic converter and a resonator. It also includes a bung for an O2 sensor. He is E-mailing me prices. Made of 302 stainless and includes bolts and gaskets with hangers for the stock locations. I am ordering one and doing before and after dyno runs once I get it. Mike

David Beale

Mine is still running fine, but still not a lot of miles on it.

One thing that surprised me - it's a lot more fun to drive, if that's possible. Maybe it has a little higher low end torque. Maybe because it's a bit quieter, allowing my subconscience to let me depress the throttle more. Whatever, I'm now looking for excuses to drive it, even in traffic. I even got it wet twice last week!

Scrub

iTrader: (25)

I'm very interested in one, prices would be nice.

David Beale

Maurice quoted someone else about $435 US plus $27 shipping. That's for the one I have - 5" cat. with O2 bung for a wideband and installation kit. See the pic. above. There was no resonator. E-mail maurice@harddata.com and he'll quote you.

MichaelFregoe

iTrader: (1)

Pipe. polished #304 Stainless steel, 5" metal wound cat, hangers and
fittings/install kit and 18mm O2 bung behind the cat: $420

2 on hand, more available in 10 days ( build just started on next
batch).

I did some checking today after we talked.
The space for the resonator is very tight, and after going over it with
Random, we think the best bet is to put the resonator separaely,
further
back on the pipe.

We offer a 9" long, 3" ID resonator for this purpose at $95
It come with one end male sleeved, and the other end female sleeved.

Scrub

iTrader: (25)

Just out of curiosity, do you know what the cells per square inch is on that converter?

-Dan

MichaelFregoe

iTrader: (1)

Check the Random web site, as they are the manufactures of the units.

MichaelFregoe

iTrader: (1)

This is from an Australian website. It compares backpressures associated with their catalytic converters and a stock converter. This should be similar to what Random is producing.

METALLIC SUBSTRATE CONVERTER - MAZDA RX-7

"Metallic substrate converters give an exceptionally high flow rate for their size compared to traditional ceramic core converters, for example the back pressure in the header pipe with a conventional hi flow cat fitted is around 4psi with a metallic substrate it is around 1.5psi (see converters for flow rate comparisons) full stainless steel construction. "

http://www.smb.net.au/fullsystemsmazdarx7.htm

MichaelFregoe

iTrader: (1)

http://www.randomtechnology.com/technical.html

MichaelFregoe

iTrader: (1)

Sorry to revive such and old thread, but I finally got around to installing the Random Technology metallic substrate catalytic converter on my car. I have a Pettit intake and ported motor, 99 SPEC turbo’s and a huge custom intercooler. The exhaust on my FD before the installation consisted of a Pettit down pipe, stock catalytic converter and Racing beat dual tip cat-back. I replaced the stock converter with the metallic substrate unit after welding the new unit together (It comes in two pieces, with a giant clamp). It also comes with a bung for a wideband O2 sensor.

Let me start by saying that the new converter FLOWS! Wow! I turned the boost controller all the way down and I still experienced boost creep starting at 10 PSI @ 5K RPM up to 14 PSI at 7500 RPM. I had to install a 2.5 inch restrictor in the exhaust to keep things under control. At idle and cruising the car is almost exactly as quiet as it was before. At WOT it screams like a have a straight though mid-pipe. Inside the car the sound level was identical.

There is a little “stink” out the tailpipe now, but not anywhere near what it was when I had a straight through mid-pipe on the car. The A/F ratio leaned out a bit (.2-.3) but I am well within safe limits. In fact the car runs very rich with the Pettit ECU I am currently running……at WOT with 12-13 PSI it runs 10.6:1.

Currently with the restrictor plate I can maintain boost perfectly at 13 PSI all the way to redline. I am going to make some changes to the boost controller tonight so I can adjust boost back to 10 PSI where I always run the car. I could most likely increase the size of my restrictor to 2 5/8 inches without any difficulty. I’ll do that after I get the boost where I want it, so that any changes will be apparent.

axr6

I had the same boost creep response after installing my Davesport metallic cat. They just flow much more than ceramic high flows. Instead of the restrictor plate I used a set of Supertrapps at the exit pipe to exactly control the needed back pressure. I did not feel good about putting in an arbitrarily smaller restrictor plate.

What I had found is that I just needed a very tiny amount of additional back pressure that can be achieved just by the presence of the Supertrapp plates but, without the usual back blocking plate. It also helped to lower the sound levels as a side benefit. Other than the fact that some people may find it ugly, it works great for me as I can control the boost creep by adding or taking out plates as required by ambient temperature conditions.

Needless to say this solution only works on single exit exhausts, particularly with the large exit pipes, such as my Corksport exhaust have.

I also welded in an air pipe in hopes of passing CA emission with this cat.

Albert

MichaelFregoe

iTrader: (1)

I changed some settings on the Profec and now maintain boost perfectly @ 11 PSI all the way to redline. Now I'll increase the size of the hole in the restrictor untill I get the perfect balence of boost control and flow.