IAC location on manifold

[PaulProe]

Does anyone have pictures of the IAC(idle air control) and its location on the manifold in relation to the venturi's and linkages.

I am in the process of setting up an EightStack system in place of my Webers and curious how others may have mounted the air control valve

Thanks

Paul

 

[Andy Green]

Hi Paul,
On my eight-stack install, using AT Throttles, I haven’t used an IAC, but use a throttle stop to bleed the idle air through the throttle blades. This work well and gives a really nice burbling on the over-run, which is what these cars is all about!<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<img src=" /><o></o>
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Andy<o></o>

 

[PaulProe]

Appreciate your comments, Andy, but I am still looking for any photos of a unit with an IAC valve installed.

Paul

 

[Vernon Witney]

Hi Paul, I've never seen this, and probably for good reason. Generally IAC's are used on production engines with a single throttle body..or at least a single point of entry into the inlet. It's fairly easy to implement and makes sense in that you can close the throttle and have idle controlled by the IAC. Move onto an 8 stack and suddenly, you have 8 points of entry. To control idle via an IAC means connections to all 8 ports, all of which have to be regulated exactly the same to achieve an even idle. It's difficult to envisage exactly how this would be done.
I know that there are some systems that join all 8 stacks together to give a collective vacuum signal...so would this work in reverse? not sure. The throttle bodies I have each have a needle idle valve, so the idea is you'd balance idle using these, just as you would balance the main throttles. I just closed them and relied on the throttle stop and the ECU controls idle via ignition timing.

I guess the other question is why do this, as I've never seen an 8 stack system with it, so kinda curious as to what the thinking behind this is. Of course, this could be one of my many 'oh yea, didn't think of that!' moments!!!!

regards

Vernon

 

[Randy V]

You would need a common plenum in order to make use of an IAC. Else you would have to have an IAC for each of the individual runners (throats) which would be a programming nightmare not to mention something that looked really bad..

 

[Scott Calabro]

Perhaps an electric solenoid to "bump" the linkage at the appropriate time to slightly increase idle speed? Like the type used on carbureted production cars with air conditioning, or anti-dieseling solenoids.

 

[Markus]

Hi Paul,

this migth help:

Stacked EFI- advise/thoughts and poll. - Page 2 - Club Cobra

On post# 40 you can see the IAC, on other engines it sit's directly under the fuel rail.... which I should have a picture but I don't find it.

If you download the Borla catalog you can also find a few pic's
https://www.borlainduction.com/catalog.html

Markus

 

[Mike Huddart]

Paul,
we did a lot of the Eight Stack systems a while back and also TWM, all with an IAC fitted. Absolutely no point having a sophisticated EFI system without one, chalk and cheese for best running.
The Eight Stack manifold should have a vacuum plenum built underneath We fitted a remote IAC connected to a pipe fitting in the center of the manifold between the throttle bodies with 3/8 hose.
The Eight Stack manifolds where a bit thin in this area for tapping a fitting and will need reinforcing but if you have a later set up from Borla/ TWM it should be OK.
The beauty of a remote IAC for a GT40 is you can hide it somewhere on the rear bulkhead without spoiling the "original" look of your fake Webers.
Mike

 

[PaulProe]

Thanks for the replies, guys, been out of pocket for a couple days.

My build uses a newer style Blue Thunder manifold, the type that includes the vacuum plenum in the center galley. Each individual runner is connected to this plenum which is accessible thru a number of different ports, so yes, vacuum signal is available and fully functional.

My intent is tractabilty with as much originality as possible. Trying to figure out where I can mount the IAC (sorry purists, Fuel Injection just works better with this feature - cracking throttle plates is a work-around at best). That is why I posted for the pictures - no reason to re-invent the wheel.

A couple have mentioned a remote location. Is there any disadvantage to the plumbing that would be associated with this? I could hook up a 3/8" tube/hose and airflow thru this would be relatively unrestricted when the valve opens - I think?

So again, my plea: any pictures?

For those who have never seen it, this is the underside of the new Blue Thunder manifold. The plenum plate has been removed to show the porting. It is held in-place with a bunch of hex screws. I sealed it well and it does hold a vacuum without issue. The plenum doesn't extend all the way to the galley vent hole at the rear so the standard road draft/PCV setup is used. There are three pipe thread taps into the plenum on the upper surface. In the top view, you can see the vacuum ports in the individual runner area.

The only drawback is with the EightStack setup, between carbs/injectors, linkage and fuel lines, it gets really crowded on top the manifold.

Paul

 

[Vernon Witney]

Nice manifold!

I have an older blue thunder manifold. Simple, but works and fits superbly.

I don't see any issue with mounting the IAC remotely. Given all the 'stuff' that has to be mounted on the manifold, it's a relief to have the option to mount the IAC off the manifold. You are effectively introducing a controlled air leak past the throttle plates, so as long as the control is there (so no leaks) there should be no issue in doing this.

I have to disagree with Mike, however. There are some significant advantages to efi and not having an IAC doesn't negate these.

I have an Emerald ECU where the idle speed can be controlled via ignition advance or IAC. Fitting an IAC would be a right pain for me, so I use the ignition idle control. When the throttle value is below a certain value, idle control is in force and is controlled by advancing/retarding the ignition. This is not to say IAC is not better, but it's not the only way.

If, for example, your engine may come under additional loads at idle, for example, an air con compressor kicks in or there is a greater electrical load on the alternator, the IAC will probably control this better as you effectively have a limited range throttle controlled by the ECU. It's interesting to note that some newer fly by wire systems don't need an IAC, as the ECU already has direct control over the throttle plates.

If my manifold had this provision, I'd more than likely fit it. Right now, I'm very happy with the rock steady idle and pick up, so not sure where the tractability concern comes from, however.

Apart from idle control, are there other benefits for an IAC? For example, does it come into play between gear shifts? I'd be interested to find out.

All the best,

Vernon

 

[Andrew Robertson]

Hi Paul,

Given that you have a common plenum to deliver the IAC air into, you've solved the problem.

The remote IAC itself can go pretty much anywhere. I imagine a run as long as 1 metre would not have a major effect so you could basically hide it. A small filter should be used so it introduces clean air. The MAP sensor should take it's signal from a different port on the common plenum. Getting closed loop idle working well is sometimes fiddly (getting PID gain settings right can be fun!), but that's an ECU tuning issue and requires good base adjustment and sync of your stacks and your TPS as a starting point. It also requires reasonably stable ignition timing settings across the RPM and MAP range of IAC operation so the IAC doesn't hunt and chase RPM changes that result from timing rapidly moving around. Some systems use ignition timing trim to work in concert with the IAC.

Hope this helps.

Cheers, Andrew

 

[Tye GT40]

I have it located between no 5 and 6 as on the pic below. Works fine.

Br
Henrik