Just picked up this FD that has some shitty "custom" hatless exhaust on it. I will be replacing the backend with the Tanabe exhaust and am now trying to figure out what to do about the cat.

I was looking at the magnaflow cat but am not sure if the size difference in piping with effect performance to much.

The air pump has also been deleted from this car. I understand this can effect the life of the cat but to what extent are we talking and is it worth me going out to source another air pump.

can i use, say the magnaflow cat with no air pump even though it has the piece to connect to the pump?

 

First off, if you need to pass emissions, you will want a stock main cat and and air pump. Winning combo there.

If you don't need to pass emissions and just want the stink gone, most any high flow cat should do. Bonez (RX7.com) has a nice high flow cat. Many high flow cats will do fine with no air pump, even if they have the air pump hose hookup.

Performance-wise, most of the high flow cats out there should be similar. As long as it's 3" piping you're good.

If you have a stock ECU and no air pump, the car will run like **** with no air pump. On/off throttle is herky jerky and idle is rough. The stock ECU fudges the O2 sensor numbers to take into account the air pump air fooling the stock O2 sensor. Only way around it is a PowerFC, and it's also one of the best things you can do for the car.

Dale

 

No emissions needed for now, just don't want to put a mid pipe there and i would rather not have the smell. Good to hear that they will still work fine even without a air pump hooked up, that was one of my concerns.

hmmmm that explains some of the things i have been noticing. PowerFC is something i plan on doing in the hopefully near future

 

+ 1 to everything above. From your join date I'm assuming you're not new to rotaries and the higher exhaust temps. Bonez is proven. Other brands...not so good with a turbo rotary. I've got a Bonez on my car that's at least 14 years old and running w/o an airpump for last 7 or 8 years. Running OMP and premix too. It's doing just fine.

 

not necessarily new to rotaries but this would be the first one of my own.
Appreciate the input, looks like i will be going the bonez route. The air pump connector that comes out of the cat, do you have to seal that when running without a air pump or just leave it open?

 

Mine is just plugged.

 

Out of curiosity, what are the CPSI and substrate types (ceramic or metal) of the two different Bonez catalytic converters? There is a 3" stainless steel converter ($420.75) and a 3" stainless steel performance converter ($651.90).

Does anyone have an interior shot of the Bonez honeycombs?

I ask because I currently run a 3" RE-Amemiya 150 CPSI converter and whilst it helps with the fuel smell it it too small and not efficient enough to help my car pass emissions, even with the air pump pipe welded directly in front of the converter to assist with converting exhaust gases at low speeds.

 

Thanks!!

I was looking at that and i believe the performance one is just the cat and the downpipes bundled together. I could be wrong though.

 

I think you are right.

It would seem most 3" metal substrate "high flow" cats are 200 CPSI max which is unfortunately not enough to pass emissions in the UK or probably places like California. That's why I'm curious to know if the Bonez might actually be a higher CPSI such as 300 or 400 since a lot of owners on here have been successful in passing smog with it. Perhaps it's 200 CPSI but a much larger surface area than my dinky RE-Amemiya which kind of looks like the size of your regular exhuast silencer as opposed to being shaped like a cat.

 

it would fail the visual in CA.

you should set the Air Pump air to go to what Mazda calls Port Air, as the name implies it is literally the exhaust ports. its more effective at lowering emissions.

i'm not sure what emissions numbers you need to achieve, but the lower the RPM and lower the load the harder the test is. to the point where a stock FD has a really hard time passing the unloaded idle test, but for the 25mph dyno test you almost don't need a cat at all, as long as you have a working o2 sensor and air pump in port air.

if you want some example numbers, the last unloaded test i did was last week (actually it took 4 tries), its a 1976 Fiat 1.8, which ended up running a cat from an FC, which is the biggest one in the world, the EGR was setup to be ON all the time, and it was leaned out the point where it just barely idles, and it did 214ppm of HC's and 4% CO at idle, which fails, and 48hc's and 1.3 CO% at 2500rpm, which passes.

by contrast last year i had a 1980 MGB, which got a dyno test and it breezed through, HC's were in the 20's, CO was something like .6%, nox was a bit high, but i found out later it was a bit lean.

for the Rotaries, i haven't had a stationary test in 20 years, but the FC's will do numbers around the same as the MGB did, with lower NOX (40hc's, 0.2co, 400nox's), a 99 spec FD or Rx8 will be single digits (4hc's, 0co)

 

First, here is my cat with the welded air pump pipe just before the cat itself. I know the stock cat injected air into the middle of the cat which is probably more efficient but I wasn't so sure about trying to do that.





Below are my emissions results with the car and we leaned out the idle and low speed parts of the map quite a lot to try to get it to pass. Fortunately (or unfortunately), this was for experimentation and we had already "passed" before this.

Emissions Results

I'm pretty sure my targets are based on the generic catalyst requirements in the UK since my import doesn't fall under the UK Mazda RX-7 regulations. Either way, the required results aren't that far off from each other but what I should have for a 1995-2002 vehicle is:

Normal Idle

Carbon Monoxide ("CO") - 0.5% (UK RX-7 limit - 0.5%)

Hydrocarbon ("HC") - No requirement (UK RX-7 limit - No requirement)

Raised Engine Speed (c.2,500 RPM)

CO - 0.3% (UK RX-7 limit - 0.3%)

HC - 0.02% or 200ppm (UK RX-7 limit - 0.02% or 200ppm)

Lambda - 1 +/- 0.03 (UK RX-7 limit - 0.97 to 1.6)


Idle






Raised Engine Speed (c.2,500 RPM)

 

I'm located in Hong Kong and MOT here is exactly the same as in UK, so I can tell ya that you will need very new high flow cat/at least a sorta ok condition main cat PLUS ALL secondary air injection working (ACV. Air pump, O2 sensor, ENGINE HARNESS) to get it to pass.

its such pain in the *** to do

 

Yeah, perhaps on the stock ECU it would have run a bit cleaner but I still don't think it would have passed with my RE-Amemiya cat as it's just too small and low CPSI. It's a shame because I had a stock cat on it before that was in near perfect condition on one end but starting to crack on the other so I replaced it before the honeycomb broke down even further.