Gut instinct tells me yes, but I wanted to run it by the forum.

Let me explain what I'm talking about. I'm the proud new owner of a Ryan Falconer ITB intake for the 60-degree V6. This intake was made for racing engines. As such, it has no provisions for idle air control or vacuum operated stuff. The previous owner did add some tubing and fittings to run vacuum accessories. But there doesn't seem to be anything for idle control. So I'll have to add that.

The big question is whether or not I can roll the vacuum and idle air stuff all into the same plumbing. I would like to combine the two, if possible, so I don't have a mess of vacuum lines all over the place. Since the intake doesn't have a common plenum, the vacuum (and idle air) needs to be distributed to / from each individual intake runner. That means running 6 vacuum lines to an air box for a vacuum source, and potentially another 6 lines to another air box for idle air.

I've been told that if I combine the idle air and vacuum circuits, the idle air will mess with the MAP sensor readings and fuel pressure. But that should (presumably) only affect idle. I can deal with a funky idle, as long as the engine runs properly at anything above idle. It's not a daily driver.

Also, I'll be running the engine on a GM 7730 ECM, with the standard OBD-1 sensors and controls, if that makes any difference. I also have the ability to reprogram the ECM.

And just for kicks, here are a couple shots of the intake.





Thoughts? Opinions? Experience? (some real-world experience would be awesome!)

I would think that as long as the flow in the individual lines connecting the vacuum manifold to the runners exceeded the flow requirements of the IAC passage, then it would be OK to have everything together (brake booster might still be an issue). The manfold needs to be large enough to buffer the individual cylinder pulses, but not so large that you create a system response lag for the MAP sensor.

Looking at the overall design of the intake, I think you could plumb in a single (or double) 1" OD aluminum tube that runs the length of the valley. Then drill the runners for some press in hose barbs and use some short sections of hose to connect the manifold to the the runners. These hoses could be mostly hidden underneath the vacuum tubes. The only concern I would have with tapping into the tubes after the injector port is that at idle, these vacuum hoses could allow cross-flow between the runners and lessen the airflow past the injector air stream. By having the vacuum hoses happen above the injectors, then the airflow would still fully pass the fuel spray.

Might PM CaliforniaKid to see how his hilborn setup plumbed.

Do remember that the stock Fiero V6 uses two functionally different vacuum sources: manifold vacuum and ported vacuum. The ported vacuum source is at approximately ambient atmospheric pressure when the throttle butterfly is fully closed, but it quickly transitions to near full manifold vacuum as soon as the throttle begins to open.

Fieroguru: what size tubing should I use to connect the the vacuum plenum to the intake runners? Should 3/16" ID work? Or should I go bigger? This is assuming I combine the vacuum and idle air into one plumbing system.

Also, the the vacuum ports that the previous owner drilled into the runners are down by the base of the upper manifold. I guess I'll have to drill new ones up higher. No big deal.

Marvin: Ported vacuum won't be a concern. Since the EGR was deleted, and the charcoal canister is now controlled by the ECM, ported vacuum is no longer needed.

Thanks for the suggestions, guys.

the Idle Air in a stock setup runs down to the actual intake manifold, not the plenums.
which means that the idle air passage also has a small port in every runner, meeting along the common channel, which will have roughly the overall "engine vacuum". so, yes, I would expect there would be no problem, as long as your vacuum source is done after the IAC, being it is only active at idle.
this also assumes you are using the stock intake manifold under that beautiful ITB setup.

quote Originally posted by Pyrthian: the Idle Air in a stock setup runs down to the actual intake manifold, not the plenums. which means that the idle air passage also has a small port in every runner, meeting along the common channel, which will have roughly the overall "engine vacuum". so, yes, I would expect there would be no problem, as long as your vacuum source is done after the IAC, being it is only active at idle. this also assumes you are using the stock intake manifold under that beautiful ITB setup.

I wish I could do that. But the Falconer setup has its own lower intake manifold (pictured above). The Falconer upper intake is not compatible with the stock lower intake. The ports won't even match up.

The Falconer lower intake doesn't have any provision for cold-start, idle air, sensors, injectors... none of that. It's very basic. The previous owner had a hole drilled for the ECM temperature sensor, near the stock location. But that's as good as it gets. The intake runners are not connected to each other in any way. They are completely separate, all the way down to the heads.

On the plus side, if I can get those (3800?) fuel rails to work, the Falconer fuel rail can probably be used as a vacuum plenum. It's the blue spider-looking thing in the cardboard box. It already has holes drilled and tapped on both ends of the rail, for plumbing fittings. I could put the IACV on one end of the rail, and the vacuum connections on the other end, to eliminate cross-talk. And the fuel injector lines could be used as vacuum lines.

[This message has been edited by Blacktree (edited 11-02-2012).]

yeah - looking at that intake, I do start to see the differences. no studs at the corners. the chevy logo in the casting. and, see how the CTS sensor is added on, no existing bung for it.

not sure what you mean by getting that other fuel rail to work. wouldnt that replace the existing fuel rail? and - ya need that.
how the previous owner use it?

do the throttle bodies have at least a single vacuum port?

but, I do like the idea of the "vacuum plenum". trying to think what you actually need vacuum for: power brakes & MAP?

quote Originally posted by Blacktree: Fieroguru: what size tubing should I use to connect the the vacuum plenum to the intake runners? Should 3/16" ID work? Or should I go bigger? This is assuming I combine the vacuum and idle air into one plumbing system.

Assuming the IAC passage is 3/8" ID, it would have an area of 0.1103 sq-inches. With the ports at 3/16" ID, the area per port is 0.0275 sq-in and all 6 of them would be 0.1656 sq-in. This would have the combined area of the passaged about 50% larger than the area of the IAC, so it should be close. If you can, you probably want to install a vacuum gauge to the vacuum manifold and see if the needle swings with the engine pulses at idle. If it does, then you can enlarge the 6 runner ports or increase the volume of the vacuum manifold.

After looking at the intake more, I would suggest drilling the runners on the valve cover side (underside of the runners) and running a 1/2" tube down each side under the runners for the vacuum manifold. If you make it a "U" shape, then you can plumb the IAC, brake booster, MAP and FPR lines to the center section, or possibly move the MAP to one end and the PFR to the other end.

Did you get this sorted out?
If you decided to go another route, I would be interested in buying it.