Idle Air Control

[LodiWino]

Is an idle air control necessary on a stack injection set-up?

Rather than plumb a runner from each stack to a plenum for the IAC, could you set the idle ignition map to retard the spark?

[bobcowan]

I don't use an IAC at all. I set the idle the old fashioned way, with a set screw. Yes, the idle may vary a bit depending on conditions - temp, altitude, etc. But not enough to matter.

I don't see why you'de want to retard the spark just for idle. But my computer is fuel only, so I don't really know. My spark is controlled by the distributer with a simple curve. Again, the old fashioned way.

[fkemmerer]

Originally Posted by LodiWino

Is an idle air control necessary on a stack injection set-up?

Rather than plumb a runner from each stack to a plenum for the IAC, could you set the idle ignition map to retard the spark?

You can accomplish timing-related regulation of Idle speed with many of the aftermarket EFI controllers. For example, the FAST XFI system can vary the iginition timing to control small errors (a few hundred RPM tops) in idle speed. Remember that that IAC does other things than just regulate idle. It is also used, for example, for dashpot functions (i.e. providing a soft landing when you slam the throttle shut at high speed). The IAC setups on TWM intakes seem to work pretty good for small block applications up to maybe 427 ci. For the really big FE motors, its hard to provide plugmbing big enough to allow the IAc to fully regulate idle. I have an IAC setup on a 482 ci FE motor with a TWM intake. The setup can raise idle speed from the target 850 PRM when the motor is warm to about 1100-1200 when the motor is cold. This is a bit marginal but still helpful when warming the motor when its cold.

[RICK LAKE]

LodiWino You left out a couple of things, how big is the camshaft in your 482, how much vacuum you have at idle. What is the system of the ECU are you running? What RPM are you trying to idle at? If you are running a solid camshaft either solid roller or flat tappet, Idling is the worst thing to that motor. I don't know which stack system you have but on some you can install an Idle speed control motor from a GM car in the mid 80's. It will work in the place of an IAC. TWM and Gessford have an Idle block for EFI Throttle body systems. You would need to custom brackets for this to work. Rick L. Fred this thread was back in Sept.

[thorconstr]

Oh Rick, You need so much pertinent information! How are you doing?

[RICK LAKE]

thorconstr Hi Al Have now had alot of time for anything. Family intervension. What new info do I need?? Pertinent Info. The words are TOO big for me. Rick L. Will do the screens in the spring if GM doesn't close the dealership I am at.

[PANAVIA]

Dont forget IACs are meant for many things.

1. Cold start up (increase AIR to rise idle point to warm an engine)
2. prevent stalling (snapping throttle shut, and the IAC will let it down from 1500 to 900 nice and easy.)
3. maintain idle set by computer based on timing advance, temp and such.

Example : car running *hot* at idle advances timing runs cooler kicks up the RPM (via IAC) to get coolant flowing.

[thorconstr]

Rick, I was being sarcastic! Geez, I my ex-wife had a problem with that! I should think about that! Nahhh!