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Corvette C3 Forum 1968 through 1982

Get Rid of Air Pump and Cat

  #1  
Old 10-23-2018, 07:01 PM
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Default Get Rid of Air Pump and Cat

I have an '81. The AIR pump is making what sounds like a bearing noise and I don't think that it is long for this world. It looks like I have stainless steel exhaust with little air pipes welded into each port. For now, until I feel like dealing with pulling everything and putting headers on, I'd like to cap the larger port that the AIR pump hose attaches to on each side that leads to each of the four little pipes to the exhaust ports. I'd like to remove the pump. I'd like to remove the Cat convert and just replace with pipe for now.
I read that the small air pipes extend into the exhaust ports and melt/droop? Some say that is only on cast iron??
Has anyone removed the Air Pump or done this? Do the small pipes extend into the stainless exhaust ports and if so, will they melt if not removed?
I'd like to talk to anyone who has experience with this.
Thanks.
 
  #2  
Old 10-24-2018, 08:51 AM
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I can verify that the cast iron manifolds did have a extension tube going into the exhaust port and exiting at the head of the exhaust valve. The ends on mine melted and mushroomed but the extensions did not droop. When I removed the AIR manifold from the exhaust manifold, then the tubes could slide out and I put small pipe plugs into the exhaust manifold.
If you remove the cat and AIR then you will probably need to remove the computer-controlled carburetor and replace it with a conventional one. You might as well block off the EGR also while you're doing this.
 
  #3  
Old 10-24-2018, 09:21 AM
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Thank you for the reply. I'm in that no-mans land between deciding whether it is worth it to pull the exhaust, cat, pump, and then the Carb, intake, and distributor. I'm not really looking to make this 190HP engine produce any more hp, but want a dependable running car. Being a 37 year old car, I can foresee a lot of the smog and ECM/comp controlled components having trouble down the road.
At this particular moment, I ask myself? Should I buy a rebuilt AIR pump and leave things alone? I have a guy that answers tech questions from Ecklers telling me that he has a case of still in the box, (with white fan) AIR Pumps from the mfg. But, how do I know what I'm really getting? No warranty, etc... Almost everyone tells me to pull the Cat and pipe it at the very least. One guy told me to just run a heater hose from the air manifolds on each side where the hose from the AIR pump connects to the check valve?? Says he had the same rig and it worked for him. Isn't the issue keeping the pipe inserts from melting by having the air from the pump flow through?
Although I am confident that I can do the work, my concern is that I don't know what the affects will really be. I keep getting one person saying it's OK to do this or that, then another turns around and says this or that will cause other problems. I've built numerous carb/hei sbc's and have avoided comp controlled and smog stuff, and am confident that I can do the actual work, but I don't have the confidence to know what affects. I'm hoping to find someone with legit tech knowledge about this.
Also, from what I can see, and the shop manual says, the ECM only sends info to the pump, but doesn't know when the pump is working. There are no sensors from the exhaust, downhill from the O2 that send info. Won't the carb adjust based on the O2 info upstream from the Cat? If I'm right, the air injection will send a leaner mixture past the O2, which tells the carb to richen up? If No air is injected, the signal from the O2 will be richer. Won't the ECM adjust to 14.7:1 at the carb based on the O2 info?
Thanks again and any direction that you can give is appreciated.
 

Last edited by Ed DePriest; 10-24-2018 at 09:29 AM.
  #4  
Old 10-24-2018, 11:11 AM
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Did the person that advised you that he put heater hose on the AIR manifolds say what he connected the other end to? Not sure what good that would do. The first thing I did was remove the AIR pump and all the connected hardware. Then I added a used set of Hooker nest-of-snakes side exhaust headers. Later in life I removed the Hookers and put on a '69 side exhaust system. Besides pulling the carburetor and blocking the EGR, you will probably have to either swap out or modify your distributor. I think the computer controls it also.
 
  #5  
Old 10-24-2018, 11:58 AM
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The guy said that he just connected the two air manifolds together with a heater hose. I agree, I don't see what good it would do, especially because the check valve is supposed to only flow towards the head, not away. That's what I mean about the conflicting info. One says do this, it works fine, and another says no way???
The ECM does control the spark and the carb fuel/air mixture. From what I have gathered, most who scrap the ECM system put on an Edelbrock intake and carb and an HEI vacuum dist. The only part of the exhaust that affects the ECM, is the O2 sensor. All the rest of the AIR pump/Cat Convert garbage has to do with environmental hydrocarbon etc... output.
What year was the Vette that you did this work on?
 
  #6  
Old 10-24-2018, 06:47 PM
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Sorry but I thought my screen name would be a giveaway. I ordered it new in 1973. I would just pick up a good used Quadrajet and overhaul it. Unless you just wanted spend money on an Edelbrock system. IIRC, the Edelbrock carburetor is a knockoff of the Quadrajet. When set up properly, the Quadrajet is a hard carburetor to beat. The only thing I found better was when I had a 65 Rochester fuel injection on mine for about a year and it was really an improvement.
 
  #7  
Old 10-25-2018, 09:09 AM
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Yeah, I kind of figured, but I wasn't sure that the '73 had smog crap yet.
 
  #8  
Old 10-25-2018, 02:47 PM
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Yeah it had EGR, AIR, and ported vacuum for the vacuum advance on the distributor. Didn't really see much of a performance change when I took all of that hardware off though. But it sure cleaned up the engine compartment.
 

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