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I have an '91 F250, 460, EO4D, down on power,...85k miles. I'm putting on a set of Hedman headers and cat connector with a cat back single pipe. It's a California truck and is going to Mexico...so the cat may not be a issue. Should I replace the factory unit with a '49 state cat or eliminate the cat completely and lose the back pressure that might be needed for low end grunt and possibly start seeing codes being thrown with performance issues...?
I see a O2 sensor ahead of the cat; however, there are two tubes exiting the the top of the cat and going forward towards the engine. What do I do with these...remember it's a CA truck.
drill out a hole in the exhaust pipe about the same length from the engine as it is now. place a bung in there for the O2 sensor and leave those hoses.
The O2 sensor is ahead of the cat and not a problem; but where do the two tubes go to or what is done with them after they are removed from the cat? The tubes come out of the top of the cat and go forward and appear to connect at the back of the engine.
Muffler shop can burn holes in the straight pipe and weld the tubes to it, otherwise the air being pumped through the tubes from the thermactor is annoyingly loud.
the 2 tubes are for the AIR system basically a air compressor that pushes air into the exhaust so it fools the sniffer tests... i mean helps with emissions... so if you can lose the cat you can afford to just leave them disconnected
The air injection system can be fully deleted, you can remove the air pump, bypass it, or simply leave it here as an idler. All plumbing attached to it can also be removed, the only things that should stay to prevent EEC codes are the TAB and TAD solenoids that control diverter valves in the system, just leave them electrically connected but remove the vacuum lines. Then it's your choice if you want to install an aftermarket cat or not, but none of these are anywhere near as restrictive as the factory unit.
No cats is definitely the way to go. I have an 89 f-250 with a 460, no cats. My compy throws no codes whatsoever. I have the o2 sensors in there (the ones that are mounted before the cats) but everything else is straight pipe. Back pressure is not an issue, I have true dual straight pipes and the motor runs strong. Loud as heck tho. If going with no cats, try to get a nice high flow quieting muffler, or just watch it around the cops.