justinpace

sorry i know this is a noob question ive been researching it for a few days but i cant find direct answers

i have an s4 gtu, its 100% stock and i want to do a complete exhaust system however i know theres an air pump and theres something coming off the exhuast system that leads to the engin bay didnt really pay attention im guessing its what activates my 5th and 6th ports?

so my question is if i do an header and complete exhuast system then id have to remove that thing that comes out of the stock system that activates my ports? thus meaning id have to remove my air pump? i just want to know if i have to take thoughs out will it decrease my power or acceleration im very confused

7fold

search!!!!!!!!

you might learn a thing or two


my 0.02, get an exhaust (racing beat) that will have a place for you to plug the exhaust into the ports so they still work, I just did full corksport exhasut and am working on making my own, its a pain in the ***.

again, SEARCH!

pfsantos

iTrader: (1)

Alright...here's the deal. The pipe you see going to the exhaust - the Main Cat to be exact - provides air for the Main Cat to do its job. The Air pump sends air to the Air Control Valve (mounted on the intake manifold just above the exhaust manifold). The ACV then sends air either to Atmosphere (outside) via the relief hose and silencer, to the Exhaust port, or to a passage in the intake manifold that leads to the hose at the back of the intake manifold. This hose goes to the split-air pipe and then to the main cat.

Near the front of the split-air pipe, there is a one-way valve, and going back, a small pipe welded to the split-air pipe. The one-way valve prevents exhaust going to the ACV. The small pipe uses gas velocity/pressure to open the auxiliary valves via the actutators at about 3800RPM.

Some Racing Beat headders have a bung welded in for the 6PI (6-port induction) system (the auxiliary ports opening via the valves, actuators and exhaust pressure are what changes the fuel air going from 4 to 6 ports).

There is some debate as to how effective the original design is/was, because as the engine and exhaust age, the RPM may vary. The Racing beat headder will similarly activate the 6PI system depending on your exhaust.

In essence, you may want to use an RPM based electronic switch, if you want the 6PI system to activate exactly at a particular RPM.

BTW, if you don't put a cat back in, you can remove the air pump, since on 86-88 cars it isn't used for 6PI. In 89-91, the 6PI system (and VDI) use air pump pressure, via solenoids and an ECU signal. Keep in mind, when removing the Air Pump, you will only have the water pump pulley spun by one belt, unless you get a yahoo belt (pineappleracing.com) or a double alternator pulley.

justinpace

thanks for your help pftsantos cleared up a lot of questions, i did search however so many threads had different opinions as to wether the s4's need the air pump or not just got a little confused

InsomniacFC

iTrader: (4)

S4's need the air pump to actuate the auxiliary ports and to pass smog.

ramses666

iTrader: (1)

So? What do you think you need to do now?!? Are you going to rig the airpump & a solenoid valve & RPM switch? or use the Racing Beat header with a back-pressure pipe? Be warned the RB back-pressure pipe deal is not exactly reliable as to when or if your aux ports will open. There's no real way of knowing how its working or when. I've been there & done that & measured the back-pressure with a gauge & talked to the designer of the header. I considered it & rejected it and built my own system that is adjustable, reliable and has verifyable function but was overkill. I plugged my back-pressure pipe. Tell us what you think.

Ramses666

bboyclo

hmmm....I will be doing a full corksport exhaust system real soon and I'm just going to do the non electronic version of activating the ports...go to the 2nd gen archive and look for it there....the guy said it cost him lil over $30 and problem is solved. GL

pfsantos

iTrader: (1)

No. From factory, S4's used exhaust system pressure/velocity to activate the 6PI system. If you read up on the Secondary Air injection system (specifically the Training Manual), you'll see that most of the time at higher loads and RPM's, the Air Control Valve is sending air to the Relief, so the air pump won't add air pressure to the split-air pipe (and 6PI) anyway.

The air pump on S4's is for emissions only. On S5's, it is used for the 6PI and VDI also.

As mentioned, on S4's, you can modify the 6PI system to use the air pump, as shown in the archives, or you can use another air source (i.e. lumbar support motor, air compressor) and some way of controlling air to the actuators.

Roen

iTrader: (2)

Please don't post misinformation.......it's grounds for a warning/infraction.

RotaryRocket88

iTrader: (7)

I went with the RPM switch setup and never looked back. It is such a huge difference considering the stock backpressure setup never worked properly in my car. Near as I can tell, even with cats in, the actuators never fully opened, and with a free flowing exhaust, there was no hope for it.

7fold

do you know if there is a place taht does a write up on this... i forget???

pfsantos

iTrader: (1)

https://www.rx7club.com/showthread.p...ght=rpm+switch

The above comes from the original thread in the 2nd gen. archive, which is:

https://www.rx7club.com/2nd-gen-archive-72/how-diy-rpm-switch-6th-ports-vdi-233381/


Another method (non-electronic) of activating 6PI:

https://www.rx7club.com/2nd-gen-archive-72/how-air-pump-auxilary-port-activation-330310/

InsomniacFC

iTrader: (4)

My bad. Just smog.