That's weird, my understanding is that the air-tube needs to be BEFORE the cat, as it gives additional air to help burn the "bad' emissions.

Check-out my melted-cat, does yours look the same ?

:-) neil

BTW: I'm in JAX, FL, as well.


more info here:
https://www.rx7club.com/showthread.p...ghlight=melted

 

The air tube of before the cat on my SMB.

 

So I swapped in a stock cat and did the test again. Apart from the cat, everything was as before. On this occasion I passed by a large margin.

Test________CO2%__O2%______HC(PPM)________CO%_____ ____NO(PPM)______
______RPM_MEAS__MEAS__MAX_AVE_MEAS__MAX__AVE__MEAS _MAX__AVE__MEAS
15mph_1768_14.30__0.80_|_88__21___22__|_0.52__0.06__0.01_|_704__150__167
25mph_2922_14.40__0.50_|_53__13____6__|_0.50__0.05__0.24_|_738__136___87

For comparison, here is the previous test:

Test________CO2%__O2%______HC(PPM)________CO%_____ ____NO(PPM)_____
_______RPM_MEAS__MEAS__MAX_AVE_MEAS__MAX__AVE__MEA S_MAX__AVE__MEAS
15mph_1771_14.69__0.16_|_88__21__120__|_0.52__0.06__0.57_|_704__150__245
25mph_2034_14.70__0.11_|_53__13__106__|_0.50__0.05__0.65_|_738__136__201

I think it is safe to say that the SMB does a **** poor job of cleaning up HCs and CO and that it is going to be pretty hard to pass smog with it without some creativity. Would be interesting to see what sort of numbers a catless midpipe would give for comparison.

 

A car with a cat-less midpipe has HC levels over 1,000 ppm (don't ask me how I know that). I put an SMB metallic cat on my car with no airpump and couldn't pass smog. The HC levels got down to 300+, and the CO2 levels were pretty high as well.

I think my car was running rich. I'm going to get my PFC tuned next week, but I'm not sure that would help. I thankfully don't have to smog my car for another 2 years, so I won't be able to tell until then.

 

Note that the stock cat also uses air injected into the CAT for the HC conversion. There is only so much oxygen available in the CAT for the HC reaction. If you are very rich, the cat is not going to be able to clean it up--period.

You could relocate the SMB's air injection pipe in front of the CAT where it can do some good, but keep an eye on temps.

 

Were you running an air pump (before the cat)?

I think it may be very difficult to pass smog with this cat even with an air pump. You can reduce HCs and CO by leaning out the areas where the test is performed but NO may climb if you do this. It might be doable (there is some margin for NO in my SMB numbers, for example) but would probably require several runs to get it right.

 

Ignore the question about the air pump - I just reread your post. Be interested to see your numbers if you still have them.

 

if you expect to pass CA emissions with an FD, I'd plan on frequent cat changes, regardless of what manufacturer you go with

in my case, it's just there so I can pass visual inspection

 

Not true. The Bonez, for example, appears to last indefinitely. Metallic cats and cheap Catco cats have been known to die frequently to be sure.

 

Well actually the main reason the stock cat works so well is because of it's sure size and honey come surface area. It's almost like having two cats in one. The cat in my 91 vert is all but gone. I'm thinking about buying a new VALUE brand version from Mazda. These are oem quality but are a ton cheaper than the originals. I also get to sell them to myself cheap Flow wise, I won't know untill I get one.

 

A couple of notes: The stock FD cat has 3 bricks in it and a large cross sectional area, with the final section being principally for HC conversion. I was able to pass CA smog, albeit barely, with my original stock cat having 159,000 miles on it at the time. When I pulled the motor last year, I noticed that the front brick had large cracks and was crumbling.

Worthy of note: Having tested cats on a flow bench, I can tell you that the stock cat has about the same flow as the so-called 3" high flow cats using a ceramic substrate. And that includes the 2.5" plumbing on the cat as well. I know it's rather heavy, but the extra shielding is well worth it to keep the red-hot (literally) cat from frying the under carriage with its radiant heat.

Based on my experience, a used stock cat in good condition isn't a bad way to go.

 

I remember being disappointed when I went from a stock cat to a Bonez high flow. My butt dyno felt nothing and (with a bleeder valve MBC) my maximum boost levels did not change. However, with the SMB my butt dyno felt plenty, my Datalogit logs showed a significant transition improvement, and I got mild boost creep.

I'd like to see a flow bench comparison between a 3" midpipe and the SMB.

 

+1

the SMB flows almost as well as a resonated MP

 

what does that really mean? 3-4 years with non daily-driving?

 

Well, not exactly.... The SMB does flow better than the ceramic cats, about 50% better at a given pressure differential IIRC. However, it is nowhere near a straight or resonated pipe, which has no significant back pressure at flow rates important to us.

An important observation here is that once you start to reduce the resistance to flow below a certain level, you start to hit a point of diminishing [power] returns.

 

Actually, I took it off 2 weeks ago to get a wideband bung welded in, and the substrate still looked fine. So now I am baffled as to why it was cleaning my exhaust air, and now it's not.

 

Are you sure you are not running very rich? You wideband should tell you.

 

I was before I got my WB. But it was because my FPR was set about 5psi too high. I had corrected that some time ago.