S5 cat removal, what to do with air hose?
 

I'm referring to the hose that connects from the lower intake manifold and runs to the air tube on the catalytic converter.

Now that I have removed the cat and replaced with a header-presilencer setup what do I do with the outlet connection to the intake manifold?

Should this connection be plugged or does it need to be able to flow air (as if there was still a cat) to keep the pressures balanced in the intake manifold?


Thanks!

BUMP...

No body else with a S5 has removed the cat huh! ;)

wat i did for my car was take off the pipe and plug up the hose that was connected to the other end of hte piping.

eric.

Thanks Eric,

By your sig, I take it that it was done on the 1991?

yup

ummm btw, what is that hose for.....?

I had it welded into the pipe that took the cats place. I don't have a header, just a ghetto pipe welded in place of the cat. I don't know what That hose is for, though.

i hear that it feeds air into the cats, but im not sure.

Are you guys talking about this one? This pipe feeds from the airpump to the cat.

http://www.imagestation.com/picture/...c/faa3e083.jpg

i also am under the understanding that it is feeding fresh air to the cats..fresh air is supposed to fuel the fire better..so the cats burn more efficiently

ummm...
 

header with presilencer....is it still loud...
my fc is about to blow my brain out.. i have no cat striahgt with hks hi power...ahh.. im thinking of gettin a presilencer.. does it work?

That pipe can be capped or left open.
On an NA with a header, silencers are a must.

There are pictures of my cheapo header-silencer setup and a sound bite linked in my sig below.

As mentioned in this thread, pumps air into the cat to help burn any unburnt fuel and thereby reduce emissions.

You dont need to cap it since there isnt supposed to be vacuum. It will just push air out under the car.

You can remove it (the whole air pump) since you put a header and all those goodies. But now you have to find a way to get your ports to open at 3800rpm.

ziptie those bitches open!

Then you get no torque down low!

Sorry, the air pump stays, I feel that it cause very little parasitic drag and does provide the pressure to open the 5th and 6th port;)

Hey, nice work on the car.

If you want, do nothing. Leaving the split air pipe open will cause no adverse effects.
You can also cap it with a large hose cap.

I'm of the philosophy now that if mazda put it there it was for a reason.

I was under the impression that this pipe that comes from the cat provides back pressure for The ACV to function correctly or more efficiently?

My racingbeat header and presielencer package came with the pipe extension that was on the cat. But before I got the RB, I had a crappy ghetto straight pipe in there with no hook up back to the lower intake manifold.....And it was a dog off the line.

The RB presilencer does not have this pipe for the proper S5 application. The reason it is included on S4's is because the split air pipe provides the backpressure to open the auxilary ports. S5 use air pump pressure.

Just because Mazda put something there for a reason does not make their reasoning correct. Ever thought about the sub-zero start assist?

Ever thought about the sub-zero start assist?


Yeah you're right about that, the sub zero isn't worth a crap.

so on an s5, i can cap it and just find a way to get it held up and i'll be fine?

Many of what Mazda designed came from making cost compromises and emissions functions. It does not mean it has purpose in running an engine efficiently, especially in cars as old as these ones with such lax emissions requirements.

By your philosophy, the catalytic convertors were put there for a reason, by Mazda, yet you removed them. Same thing applies here.

However this is the exhaust system I have.

http://www.mazdatrix.com/pictures/racing/r8-rb.jpg

It is sold for the 86 through 92 completely and does accomodate for the hose..: