After a little discussion yesterday about exhaust pressure being used to operate the port actuators, I went digging through some parts. I found that a series 5 split air pipe will only allow air to flow from the air pump to the cat. I was hoping I could use the pressure from the exhaust through the split air pipe to supply the needed pressure to open the 6th ports and VDI. I guess I could cut off the valve section that prevents flow back to the air pump, but I'm beginning to think that there will not be enough pressure in that line. If in stock form the air pump was pushing air into the cat through that pipe, then there must have been more pressure from the pump than the exhaust or the air from the pump would have never made it to the cat. Does anyone know how much air pressure would be present through the split air pipe hooked up to a presilencer?


91 vert

 

Depends on what cat back you have installed. If you're running something aftermarket, then I doubt it. The only way to tell would be to try it.

You might get enough pressure, but it may not be at the desired RPM range.

 

I have a custom 2.5 single and a straight through dynomax muffler 2.5 in x 2.5 out. I honestly don't see it working.

 

samps:

it looks like you want to have (on your S5) a setup similar to what's on the S4. Right ?

on the s4, the exhaust pressure finds it way to the actuators from the cat via the split air pipe via a tee just before the check valve (which prevents exhaust gases to go back to the ACV)

in your case, with your setup, as wozzoom said, they probably will open but at higher rpms, maybe 4,500

hugues -

 

OK thanks hugues, I was unaware that the series 4s used a "T" before the check valve. I was wondering how the series 4s worked; I thought maybe they had a different split air pipe without the check valve. I guess I could just leave the airpump in and just try out the split air pipe to see if it works. Anybody have any ideas on how to increase the pressure in that line without plugging up the exhaust? How about decreasing the diameter of the outlet? And do you think the heat from the exhaust will damage the rubber inside the actuators?

 

Another option: Maybe I could try just wiring open the 6th ports and use the split air pipe to actuate the VDI only. I have a GTUS rear so I'm above 4 grand most of the time anyways, and the VDI seems to have a much bigger impact on performance. Although I would prefer to have both systems fuctioning.

 

You're talking S4 here, right.
The S5 ports open up via air pump pressure only (I think).

The injected air from air pump to the cat via the split air pipe and the exhaust flow "add up" in terms of the pressure you would see at the actuators (at least, that's how I see it)

but then what do I know ? since everybody says that on the S4, only exhaust backpressure opens the port.

hugues -

 

Just curious. You have a 91vert, a series five. What's the deal? Did you take the airpump off? Or do away with the solenoids for the VDI and aux ports?

On a series four, the tee for the aux ports is b/t the checkvalve and the cat. The amount of air from the airpump/acv varies. When the pedal is to the metal, the relief valve on the acv opens and dumps overboard, so there won't be much air going to the split air pipe. Something to take into consideration.
I just wrote because I can't figure out what your up to.

 

You'll see the best results having both systems working properlly.

I honestly think you should try to pursue the electronic actuation of the 6-ports and VDI. On my "86 Mutt", I opperate the VDI and 6-ports with one RPM switch and one of the left over solenoid valves from the vacuum spider. When I dynoed the 86 last september, I picked up about 12 RWHP on the bottom end having the 6-ports open at 4500 RPM vs. wiring them open.

To actuate your system is very easy, all you need is an electric air pump and a 12V relay! You can dig up an air pump from an old cadillac, a late model Vet or buy one for around 30-40 bucks.

Wire the 12V relay to your existing 6-port actuator solenoid so that when the solenoid sees power, the relay switches. Then run 12V power from the battery to the air pump. When the relay kicks on, the air pump will kick on and provide you with more than enough pressure for the VDI and 6-Ports. PM me if you have questions.

Jeff

 

Hehehe, HAILERS! Sorry, maybe I didn't give enough info. Right now I have the air pump running directly into a single hose which has three hose barbs in it. Two of the barbs go to the 6th port actuators and the other goes to the VDI actuator. I do not have any solenoids or any of the spider in fact. I also do not have the ACV. My system includes only the air pump and the actuators. It has been working flawlessly for about 6 months now, but it has some drawbacks. The air pump is routed into a single hose which just dumps air right on top of the headers. The air pump is pretty loud for those of you who have never left it vent to atmosphere (that little silencer was there for a reason). Anywho, the car is loud enough as it is without the added noise from the airpump.

Here is a pic of what is going on now. I would like to just replace the airpump as the source of air pressure with the exhaust. I am not worried about smog, this car is mileage exempt.

 

Question: Did you also rip out the VDI and 6-port Solenoids? Or do you have the 6 ports and VDI connected directly to the airpump?

 

WOZZOOM:

sounds like a good setup (with electric air pump) !!!

Hugues -

 

They are connected directly to the air pump via vacuum hose. The pic pretty much says it all. I still have all of the solenoids and even located the corresponding wires from the ECU that used to control the solenoids. An electrical setup is another option, but I like mechanical things.

This is not so much of a modification; it is more of a "I'm gonna be bored on Sunday, what can I do to the car" type thing.

 

Quick semi-related question:

On an S4 with no air pump/acv, what should I do with the split air pipe? The "T" goes to the actuators as normal, but the other end of the check valve is open to the air. (because there is no tube going to the air pump) Should I plug it or leave it as is - or does it make no difference?

Thanks

 

You can leave it open. Air cannot flow out of that hole since it has that check valve.

 

this is so easy to do with the S5 cars. Everything is already there... all you have to do is supply the air pressure.

Now if Samps wants to try this method with exhaust back pressure instead of wiring in an electric air pump???

 

I'm not AGAINST the electrical option. I just would like to give the back pressure route a chance first. If it does work it will be very crude without any type of adjustment and may even prove to be unreliable in the years to come. But I can do it at home without actually buying anything and it will be easily returned back to the way it is now if it does not work. I have spent thousands on this car and money is not really an issue, I really just like to fart around with stuff when I'm bored, and electrical equipment doesn't usually present allot of farting around opportunities.

 

Exhaust pressure is max at beginning of exhaust tract, so I would put the pressure pipe feedin the actuators as close to the exhaust port as possible, but

is it enough to open the ports, that I don't have a clue

also, the exhaust flow is a pulse that is pretty much undampened so close to the ports, so that could create problems but I assume, at high rpms, that might be ok.

hugues -

 

I have no plan on making any holes in my exhaust. I already have a Racing Beat presilencer which has that little tube hanging out the side of it. Right now I have a bolt threaded into it to plug it up. But I can connect the split air pipe to it within minutes and run some hoses. It probably won't work but if nobody can say it deffinitely won't work then I'm gonna try it. Even if it doesn't work, it will at least prove that it can't be done and I can just go about my way.

 

yes, that's the spirit, let us know how it turns out

Hugues -

 

I am sooo lost by this damn thread, to put it simply, you are trying to get your 5th and 6th ports working becuase you have a strait through exhaust...but essentially they should be working becuase arent the s5's only actuated by electric anyway? or something? i thought they stilll worked with strait through exhaust.

 

Didn't work! Not enough pressure. The actuators didn't open up untill almost 7k and anywhere under that they were bouncing violently. This idea should go away now.

 

what is a VDI and at what RPM do the ports open up at on a stock '86 base model? Thanks

 

The 86 base does not have a VDI (Variable Dynamic Intake), this feature was only available on the series 5 (89-92). The ports should open at about 3800 rpm.

 

So are you ready to make a trip to the junk yard yet? All you need is an electric air pump and a $5 dollar relay from Radio Shack to make your 6-ports and VDI totally electronic...