josh greene

I have clogged CAT's need to rplace them, Im thinking of the RB down pipe/presilancer combo. My question is what exactly is the SPLIT AIR PIPE for i searched and got mixed answers. also any suggestions on CAT replacement would be great, i dont have much money to spend so im looking for cheep.
THANKS J GREENE

OverDriven

If you don't have to pass emissions any time soon, I would replace the cat with a straight pipe to eliminate it all together. The split air pipe is controlled by the ACV and injects air fromt he air pump into your cat to cool it. Without that, your cat will overheat and burn out quickly. So to answer your question, if you have a cat then you need it. If not, you can ditch it as far as I know. I mainly know about TII's though, so if this does not apply to N/A's then someone correct me.

-Joe

Kenteth

... Ermm.. Well as far as the chemical composition of cat's...

The Catatlyic converter needs force 02 to opperate *well*. At least as goes for stock cats. Aftermarket cats use slight beefed catalyst that use 02 from the combustion.

Anyhow the reduction catalist is something like 2NO --> 2N + O2, or 2NO2--> N2 + O2. Catalist is generaly platinum, rhobidium, or a mix of both.

The Oxidization Catalyst goes something like 2CO+O2 --> 2CO2

---

Generaly on your standard car, the 02 sensor tells the ECU how much O2 is entering the cat. The computer decideds if this is enough or not enough 02 to completely oxidize the carbondioxide and to redux the nitrogen-crap. If the ECU senses there is too little oxygen, it can do one of two things:

1) Change fuel ratio/injector width's
2) Inject O2 Directly into the exhaust/cat.

Generaly just changing the fuel ratio isn't substantial enough to feed the cats enough o2. This is especially true at startup. During startup, the car runs rich, and little unburnt 02 is making it to the exhaust. Not to mention that the O2 sensor isn't hot enough to provide the ecu with an even close to half assed accurate O2 reading at during startup. Anyhow during startup 02 is hence injected idrectly into the exhaust via the airpump and ACV to makeup for the loss.

Also, if you were to constantly inject 02 into the cat, it woudl burn the cat out in less than a month. O2 is not used to cool the catalytic converter. Infact, the Cat would run *much* hotter feeding it 02 constantly. 02 is fed during cold starts as well to help heat the cataylic coverter, not cool it.

Just the same, not feeding it o2 will clog the catalyitc coverter ebcause it won't have enough o2 to keep the catalyst running to spec.

Force 02 all the time
1) burnt cat in a few months
2) hot cat
3) but cat would be effective until quickly dies off, excess 02 just makes its way to the muflers

Force O2 never
1) Cat will take longer to heat up
2) cat not as affective
3) Cat will clog.

There are however, as i mentioned earlier catalytic converters that use a different, more beefy cataylist that require less O2. These type can usually suffice well off what O2 is not burnt from the combustion process. The ECU can usually accomadate enough fuel ratio change to keep the cataylist more than busy/happy.

Final thought:

If you remove your cat and put in either a straightpipe, or DP/Silence combo, you will no longer have a use for the split air pipe/o2 injection. You can leave teh line uncapped at that point, or start removing all emissions crap since you'll be dumping crap that creates O3-ozone into the atmousphere

Oh, and No Cat:
1) You won't pass emissions without
a) a hookup
b) tank partially full of alcohol
c) standalone running your car friggin lean as hell, still probably wouldn't work though.
2) Understand why Fc'ers complain about exhaust smell. You probably have never smelled uncorked rotary exhaust. Prepare your eyes... prepare your eyes! You have been warned.

chem114 guys

Kenteth

And incase you didn't already know...

the split air pipe is connected to a line that goes to the ACV. When the ECU Deems appropriate, it opens a solenoid valve that forces 02 (via the airpump) into the split air pipe and down intot he catalyitc converter for redux and oxdiate reactions.

Kenteth

Oh... I believe my catalysts may have been wrong!

Redux is Platinum and Palladium, Oxidizers are Rhobidium and Platinum. Sounds better

hugues

split air pipe has dual purpose:

- opening of aux. ports
http://www.geocities.com/huguesdc1/intakeair.html

- feeding air to main cat directly under certain driving conditions
http://www.geocities.com/huguesdc1/secondary.html

hugues-

josh greene

this is the argument every one seems to have and im trying to clear up, some say that the split air pipe opens the aux. ports others say it does not???????

OverDriven

Aren't they opened by exhaust backpressure on the S4?

-Joe

hugues

The aux. ports actuators are connected to the split air pipe via a tee .. that's how they get their pressure to open from the exhaust backpressure.

The split air pipe is just a pipe that conducts air/pressure from one point to the other.

One could argue that the air pump might have something to do with it also under certain driving conditions since it tees into that actuator line, but that would confuse people. The general consensus is that exhaust back pressure is the only responsible for opening the aux ports (I don't fully agree but it's probably moot point).

you could probably ask HAILERS to monitor the pressure at the actuators at different rpms/load.

Hugues-

Icemark

The aux ports on a stock 84-88 non turbo 13B are actuated more by exhaust pressure, than back pressure. But yes it is done by the Split air pipe.

If you look at how RB makes their pre-silencer it makes much more sense to say exhaust pressure, rather than back pressure.

The dump for the ACV into the stream happens in 5th gear everytime, so that pretty much rules out the thought that the air pump feed through the ACV and split air pipe have any effect on the stock aux port operation on a 84-88 13B.

josh greene

so if i buy the Racing Beat down pipe and presilancer and leave the the hose for the split air pipe disconnected will i be fine???

Syonyk

If you own an 87 NA, as your username "tagline" seems to indicate, you'll want to leave it connected to operate your 6th ports (unless they're removed or wired open). You don't need it connected to the air pump, though.

-=Russ=-

josh greene

yes i do have a 87 NA does the racing beat pre-silencer have the connection to connect the split air pipe?

Syonyk

That it does. It has a "ram-air" intake style that goes to the split air connection.

Looks like this, and connects right in.



-=Russ=-

josh greene

AHHH NICE LOOKS GOOD thanks! youe selling that???? LOL

Syonyk

No... that's currently secured to the underside of my car. I just took a picture of it before I installed it.

-=Russ=-

Kenteth

well ****... helpful picture, I never knew thats what it looked like

totallimmortal

depending on what catbak you run you may not have enough back pressure to actuate the aux ports. If your still running stock cat back it should be fine but i'd go ahead and do it and if the aux ports don't open then do a search as there are alternative methods to open them

Sideways7

iTrader: (7)

As Icemark said, you dont need any exhasut backpressure if you are running the RB presilencer. It runs off of the pressure of the exhaust going into the tube in the center of the presilencer (see picture). You can have no catback at all and still operate the aux ports with this setup. As far as I know, RB is the only one that does this, which is why it is the only one that reliably opens the aux ports.

ddub

I'm glad I dont have aux ports to worry about anymore. Much easier to just have them gone so you don't have to wonder if they're opening

Madrx7racer

I have the SAME PROBLEM.........except that I do not have the pipe on the engine....it is gone. Do I need to cover it up with a block off plate to drive or can I leave it open?

Icemark

No, you need the line if you want to activate the aux ports