So i know a little about engines and mechanics but I'm by no means and expert or even have in-depth knowledge, especially with the more technical mechanical aspects of engines and the control/managements systems. My expertise is in Industrial Electronics & Communications, so I'm technical and I can Test, troubleshoot, bypass, engineer, modify and so on, but I don't know enough about how those management systems work to do much. I do know a little about mechanics in general haveing grown up on a farm working tractors and every other type and piece of equipment you can imagine. That being said, I have a 1987 C4 with the 2 cats coming off each side of the manifold then one bigger cat further back under the car. Removing the center cat would be fairly simple as all it has is a pipe going back to the air pump.

1st question. If i remove that center cat, do i just cap of the pipe at either end or anything i have to do?
2nd question. If i wanted to remove the 2 small cats coming off each side of the manifold, what becomes of the oxygen sensors? how does that affect the management system and what can I do to fix, bypass, or compensate?
Hoping someone can shed some light on this for me.

As a side note, the exhaust pipe broke right behind the big center cat that goes to the muffles and is dragging so I have to do some exhaust work IMMEDIATELY. Since the exhaust system on that car is choked fairly well, I want to use the repair opportunity to do some upgrades.

 

Assuming you do not have emissions testing, You can remove it all. No codes. 1 o2 sensor. On my prior 1989 coupe, I replaced the front y pipe with a new one that had only the center cat and a rear with crossover and no mufflers. Added flowmasters later. 20 years ago.

My current 1989 roadster. Front cats already gone, I cut everything out from about steering wheel back. Fitted a true duel system with h pipe and chambered sections for an LT style ‘92-‘96 car. Made it feel like a Vette. A little loud and I may fit mufflers at some point or headers with bullet cats.

Neither of these setups caused any drivability issues or codes. The factory exhaust y pipe setup from ‘75-‘91 simply sucked.

 

And, do not cap the pump line to center cat. I disconnected the rubber hose to the metal line that went to center cat. It now blows air into the wheel well area.

 

Thanks for the Info.

Yes. I'm not concerned about emissions testing. Today I just ordered a front Y pipe to eliminate the front Pre-cats. I also ordered the Flowmaster Force-II cat-back system. All I have to add is a small section to join the 2 halves when eliminating the main center cat. I heard a sound demo of the the Flowmaster cat-back, the Corsa cat-back, Mangaflow cat-back. The Corsa sounded bad to the bone, like a demon, but It was quite loud with a bit of racking and If i remove the center cat, it's going to be even louder so i didn't want that. If it could have had the same sound but quieter, then i would have gotten it. The Mangaflow didn't sound very good. It could possibly be better without the cats but, didn't sound like a corvette. It was high pitched and sounded like a Ferrari, so I don't want that either. I opted for the Flowmaster because it had a deeper resonance and sound like a corvette should sound with slightly louder that the chocked factory system. I figure that removing the cat will increase it a bit and let it breathe better. I will be deleting all 3 cats so this is why I need to know what to do with the pipe that goes to the main cat and the 02 sensor.

 

Good to know. I will disconnect the the same rubber hose for now. I have a air pump eliminator kit ordered. So what becomes of the 02 sensor? It is mounted right below flange where the new Y pipe will bolt up. Do i leave it connected and zip tied? Wouldn't that throw off the fuel/air mixture? Would it be better to add a bunghole to screw in the 02 sensor? How would that affect fuel/air mixture? Or is there another solution?

 

I found a solution. I'm going to weld on a 02 bung saddle on the new Y pipe just below the manifold flange.

 

Good plan. I don’t see any issues with that. My ‘89 with no cats, disconnected AIR pump hose in wheel well, h-pipe, and no mufflers has the O2 in stock location. No codes or CE light.