I'm getting ready to make-up my own metallic catalytic converter (w/resonator), and my understanding is that I need to place the air-pump connector BEFORE the element.

However, my muffler man says if I don't want to create a furnace and possibly clog my cat, I may want to place the air-pump AFTER the element.

Currently, there are no emissions testing where I am in Florida, and I don't want my exhaust to smell.

What should I do ?

BTW: I'm also going to install an O2-sensor bung BEFORE the element for tuning purposes.

Thanks,
:-) neil

 

I'm curious as well.

 

Airpump connection goes BEFORE the catalytic core. Check the Knightsports and the SMB metal core cats, they both have the airpump connection, before the core.

The stock cat has 2 cores and the airpump connects in the middle to supply oxygen to the second element.

The added oxygen is used by the catalytic converter to help it clean the exhaust. There's a higher risk of clogging it if you don't have the airpump or have it connected after the element where it won't do anything.

 

Which brand did you get - Random, Dynatech or something else?

First off, you do not need the air pump hookup with the metallic based cats. The metal core cats are designed to not need it. The only possible reason you might want to be using it is to somehow dilute the exhaust gases by adding more clean air (which incidentally will contain more oxygen - remember this comment I'll get back to it in a moment).

Some people may decide that they want to use the air pump for the previously mentioned dilution effect thinking it will help pass smog by passing in fresh air into the exhaust. The fresh air will also contain more fresh oxygen. Oxygen is known to burn easily and make a fire hotter and that is what it does when it interacts with the chemicals coating ceramic cats especially and probably metal cats. In old fashioned ceramic brick cats this was necessary. In metal cats, this apparently only serves to heat up the metal core further as is not necessary.

Lastly, I could be wrong about this (I doubt it) but adding the airpump hookup after the cat serves absolutely no purpose.

From what I have researched (hopefully I have interpreted all that info correctly) and was told by the engineers at Random, you don't need to add the extra air to the metal cats.

 

more info here http://randomtechnology.com/technical.html

 

I'm using the Dynatech with the air tube mounted before the cat. My reasoning for the air tube is, my RX-7 runs rich...richer, I suspect, than most cars Random has tested. Rich, by definition, means there was insufficient oxygen to burn all the fuel. By adding oxygen at the cat, I hope the unburned fuel is oxidized. That's my theory
While I'm only driving it for a couple weeks, I can say 1) the exhaust doesn't smell anymore 2) I no longer have black soot and oil residue on my white bumper 3) the car is louder than my previous high-flow ceramic cat.
I am going to add some kind of muffler directly behind the cat.

 

There is a misconception about Cat's and how they work and the need for or not of air injection. The ideal byproducts of combustion are H2O, CO2 and N. HC's are obliviously a byproduct of rich mixtures and thus more oxygen added into the exhaust in front of a Cat will permit more and cleaner burning and break down into the desired products . NOx and CO are byproducts of lean mixtures and would be improved be running richer but less fuel efficient mixture. As you can see it is kinda hard to get both at once (add oxygen or remove oxygen).

The tried and true original way was to run a rich mixture producing low NOx but high HC into a low oxygen 1st Cat to split the remaining NO, then inject air and thus Oxygen (and as a byproduct more Nitrogen), over a 2nd Cat bed to oxidize the HC and CO into H20 and CO2

The first three-way cat added Rhodium the improve NO reduction such that the engines could be tuned leaner (but still rich) for improved fuel efficiency and lower HC & CO production and still injected air to finish the oxidation.

Today's latest cars are using three-way converters without air injection by using the dual lambda feedback loops (o2 measurement upstream and down stream of cat's) with faster ECU processors to continually keep the engine running at a near lean mixture. These cats are the metal substrate cats that offer high flow rates, but it is the engine management system not the Cat itself that permits elimination of the air injection.

Guys, we want and NEED rich mixtures, thus for clean exhaust we Need air injection .. regardless of yesteryears Cat converter or 21st century Cat converter.

 

That's the best description, and it correlates to my findings elsewhere.

Air-pump connection BEFORE the cat element it is.

This forum is awesome!

:-) neil

BTW: the metallic cat element I'm using is from IPF of Japan. It is identical to the Dynatech, and only $120.

 

Does anyone know the Cells per square inch on the dynatech cat, the IPF one and the random tech cats?

-Dan

 

300

 

300 for what? The Random tech one or the dyna tech one? Thats a pretty high count either way eventhough they're probably thinner cells then in a regular cat.

 

both the random and the dynatech are 300 cells per square inch. give them a call if you want to verfify for yourself.

it's actually not that high. catalyst companies and major manufacturers are testing higher cell count metal substrate cats to try and meet more stringent emissions.

 

Eventhough Apex doesn't sell it over here yet they make one that is 130 cpsi. But I will call the individual companies, thanks for your help

 

really, cool. i wonder how that would work.

 

Ive been contemplating building my own metallic substrate cat as well and have a few questions for you.
- Is the IPF unit stainless steel?
- What is the pipe diameter - inlet and outlet - ID and OD?
- Where did you purchase your IPF unit?
- Do you know of any data regarding how these cats fare under basic emissions testing when used on the 3rd gen?

thanks,
chuck

 

Most of the Metallic Substrate cats here are very small in length. The Apex unit is longer then most metallic cats which allows them to use a lower cell count. The only downside is the cost. It's about $1000 delivered to the US.

I found this site http://www.metalsubstrate.com/pages/pmgc.html it seems that you can have custom cats made with pretty much any cell count you want. I'm gonna try giving them a call to see the cost and some more stats.

-Dan

 

I got one from SMB to try but it was too loud.
I then bought a magnaflow muffler (the same one that is in the RX7store resonated midpipe) and had BNR weld it in before the cat. We had to move the cat to just before the flange for the catback exhaust. So now it is the dp, mp with muffler first then cat, and the apexi n1 exhaust. I also requested smb to leave the airpump tube off when I ordered the cat. Now my exhaust is very quiet, doesn't stink, and doesn't leave any soot on my white bumper. I am really happy with it. The wife loves it too!

On a side note, I looked up the 5x8 oval magnaflow muffler up on thier website and it was $150 something. Also on their website is a list of suppliers. O'Reily's autoparts is a supplier and they got me the muff for $115 out the door.

Sorry I can't add any pics, I forgot to take my digi cam down when we welded the muff in. Hopefully the next time it's on a lift I'll be able to snap some pics.

 

Do you have any power numbers with the cat on? I know that cat is pretty good, it came from Aus. right? I was considering doing the same exact thing, basically some metallic cat and some resonator....I'd like to quiet my car down as much as possible.

-Dan

 

hey scrub, if you are doing a custom install like that you can also install the resonator in the long exhaust piping after the midpipe area. i read somewhere on this forum once that acoustically installing a resonator in that area yeilds better results. something about length of sound waves and what not.

note that this is second hand knowledge so it could be wrong...

but it still might be easier to fit any resonator in that area than in the midpipe with a cat.

 

I was considering that as well. JIC acutally offers my exhaust with a resonator in that section now, but I bought it before it was an option. Trying to fit a resonator onto the midpipe might be a close fit.

I'll be calling that company to find out more information on their products shortly if anyone is interested.

-Dan

 

I emailed them, they claim to be the supplier for Dynatech, Random and Vibrant. The keep in stock 200 cell density 2.5 and 3" inlet outlet 4" diameter core cats. Here's a copy of the email:

The items that we stock are a 3.0 in/out and 2.5
in/out in a 4.0OD body, total length of the converter is 10".

All of the companies in the US that sell metallic converters
(Dynatech's
Powercats, Vibrant's, Random Technology's...ect) all use our metallic
core.
All of them have the same internal metallic component made by us. They
all
just package it differently.

Regards,

Mike VanPatten
Performance Industries
mvp@metalsubstrate.com
847.426.0978 voice
847.426.1952 fax

 

hmm, interesting.....I wonder I'd like to find out what the flow ratings are for those converters. I'd also like to know how much flow is restricted and power is losed with the use of a metallic cat....I have a dyno readily avaiable to me so I may purchase one of those and do some testing.

Thanks for posting that btw

 

My car has a PFS intake and intercooler, stainless downpipe, the PFC, and an HKS Superdragger cat-back exhaust, for reference.

I have just added the 5" Random metallic cat., installed about a month ago. No air injection (in fact no air pump on the car). The cat replaced a mid-pipe, and I didn't notice any power reduction - in fact the car -seemed- more powerful. Perhaps it now has a bit more torque in the lower RPM range. It's more fun to drive, perhaps due to this torque or perhaps due to the lower noise level, or both.

Just got back from a 2700 km (round trip) to the coast. No more smoot on the rear bumper cover! Car still pulls strongly on both turbos, normal transition etc. so I reason the cat is not clogging - at least not quickly.

As I posted elsewhere, the cat reduced the sound levels by about 3 dB (that's a reduction of 1/2). The car is still louder than I would like, but no longer unbearable on long trips - ie I don't get a headache, or severely fatigued. If I were doing it again, I would put a "resonator" in line with the 5" cat. I believe Random is doing this now and offering it for RX-7s. Mine has a "bung" before the cat for a wideband O2 sensor. I am not currently using this. The Random product fit perfectly, much better than the mid-pipe I removed. My exhaust tip is now perfectly centered in the stock rear valence cutout (used to touch the inside edge and melted it a bit). I got the unit from "Canzoomer", whom I do electronics work for from time to time. email Maurice@harddata.com for a quote if you're interested. It isn't very expensive.

I now have a completely stainless exhaust, 3" or larger all the way! I'm happy!

 

Hmm good info, but are you on the stock twins? The stock twins don't flow as much as a single making anywhere between 380 and 500 wheel horse power...my only concern is flow restrictions at higher RPMs. But the info you have provided is great. Did you say random technology now offers a complete midpipe with a metallic cat and a resonator?

-Dan

 

Yep, could you (David) elaborate on this some?