MSD Atomic EFI Install - '76
Thread Starter
Pro
Joined: Aug 2000
Posts: 708
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From: Montrose CA
Shark:
Good point about the injection location... As mentioned above the 1976 model only had injection downstream of the ramhorn manifold on the passenger side whereas those in your pictures have the injection at the manifold inlet. And studying a 73 (?) model at the car show - I noted they had the air injection up high much like the approach shown in the picture.
Perhaps there is an automotive engineer so deep into retirement that they can tell the truth about what was the approach for AIR injection anyway... was it just dilution of the exhaust for testing purposes or was it to add oxygen to somehow continue the burn in the exhaust pipe or something to do with the catalytic converter (of course they added AIR before catalytic converters).
The whole topic kinda makes you want a car that is not subject to any of these restrictions and conditions.
Carl
Good point about the injection location... As mentioned above the 1976 model only had injection downstream of the ramhorn manifold on the passenger side whereas those in your pictures have the injection at the manifold inlet. And studying a 73 (?) model at the car show - I noted they had the air injection up high much like the approach shown in the picture.
Perhaps there is an automotive engineer so deep into retirement that they can tell the truth about what was the approach for AIR injection anyway... was it just dilution of the exhaust for testing purposes or was it to add oxygen to somehow continue the burn in the exhaust pipe or something to do with the catalytic converter (of course they added AIR before catalytic converters).
The whole topic kinda makes you want a car that is not subject to any of these restrictions and conditions.
Carl
Hey, cool, another bay area guy. 
If you look at the first pic of his thread, it looks like he has the AIR hooked up in the default location. I would imagine the same thing, as you're injecting raw oxygen into the exhaust and it could skew the mixtures a little leaner than they actually are. Of course, I'm fairly confident the air pump pulse is a MUCH smaller contributor to O2 readings than the combination of cylinders.
I'm no expert, though. I know GM was using AIR w/ E4ME (feedback carb) cars in the "wrong" position.
It looks like the LG4, L81 and L83 (crossfire) all had AIR at the highest points in the port; i.e. before the O2 sensor. And sure, those are low-tech motors but the C5 had the AIR input in the same spot as well, as near as I can tell:
They could have solved AIR input with the computer, of course, but I don't think it would be trivial with only a narrowband system available, and that would be erring on the side of danger (skewing the mixture towards lean once you start pulling fuel to compensate for AIR).
If you look at the first pic of his thread, it looks like he has the AIR hooked up in the default location. I would imagine the same thing, as you're injecting raw oxygen into the exhaust and it could skew the mixtures a little leaner than they actually are. Of course, I'm fairly confident the air pump pulse is a MUCH smaller contributor to O2 readings than the combination of cylinders.
I'm no expert, though. I know GM was using AIR w/ E4ME (feedback carb) cars in the "wrong" position.
It looks like the LG4, L81 and L83 (crossfire) all had AIR at the highest points in the port; i.e. before the O2 sensor. And sure, those are low-tech motors but the C5 had the AIR input in the same spot as well, as near as I can tell:
They could have solved AIR input with the computer, of course, but I don't think it would be trivial with only a narrowband system available, and that would be erring on the side of danger (skewing the mixture towards lean once you start pulling fuel to compensate for AIR).
Last edited by Carl in LA; Jan 7, 2015 at 12:05 AM.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
I've been looking at this thread recently for "reasons" and I decided to re-up because I've done some research.
Later model cars have a diverter valve that switches from in-manifold AIR tubes to tubes in the catalytic converter after a warmup threshold is reached. This is one of many reasons why ECMs do not go closed loop until a certain ECT is reached. In other words, the O2s are not polling until after the AIR pump is sending its pulses downstream of the sensors. It injects into the manifold prior to that.
MSD's Atomic EFI "AIR pump" setting does the same thing.
Later model cars have a diverter valve that switches from in-manifold AIR tubes to tubes in the catalytic converter after a warmup threshold is reached. This is one of many reasons why ECMs do not go closed loop until a certain ECT is reached. In other words, the O2s are not polling until after the AIR pump is sending its pulses downstream of the sensors. It injects into the manifold prior to that.
MSD's Atomic EFI "AIR pump" setting does the same thing.
Instructor
Joined: Jul 2013
Posts: 110
Likes: 4
From: Northern Virginia
Fi-Tech EFI for a '76 Vette
Would anyone know if the Fi-Tech EFI throttle body will allow the stock air filter (over-radiator snorkel) system to fit back on the engine? I can't fit any after market, old school 2-3" tall air filter under my hood with a GMPP LT-1 styled intake and, personally, I want the car to have the stock AF assembly on it. The drivetrain is modified, but looks completely stock from appearance and has fared well at car shows...
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Would anyone know if the Fi-Tech EFI throttle body will allow the stock air filter (over-radiator snorkel) system to fit back on the engine? I can't fit any after market, old school 2-3" tall air filter under my hood with a GMPP LT-1 styled intake and, personally, I want the car to have the stock AF assembly on it. The drivetrain is modified, but looks completely stock from appearance and has fared well at car shows...
The Fi-Tech system uses a pretty standard Holley style air cleaner flange, same as the Atomic EFI. My 1978 Corvette air cleaner had some notches to match a Quadrajet style flange. Same circle diameter, but the Q-Jet has some reliefs to locate the air cleaner. To stick a Q-Jet style air cleaner on a Holley style mount, you need to bend or remove these notches in the air cleaner. It will work fine otherwise. Good luck!
