Running cat-less

[Qxx4]

Hey guys i was wondering how could removing cats effect power and would it make the car really loud? I heard their are 4 cats in our pathfinder/qx4 is it right?

P.S i know its illegal i am just being curious. Thanks

[centralcoaster33]

Yeah, I don't see your year listed, but there are 4 cats on current models. The cats act a little bit like a muffler, so the exhaust would be slightly louder if you gutted them out. Back-pressure would be reduced a tiny bit. Your secondary O2 sensors are after the primary cats, so they would no longer read the same air, so they would send a different signal back to your engine computer, so the computer would adjust your air/ fuel ratio differently than if you hadn't gutted them. And, of course, your exhaust would not have the smog converted so you'd be polluting the air that much more. With millions of cars driving around, it's nice to have millions of catalytic converters in operation.

[Qxx4]

Thanks for the answer and my qx4 is 2003 but in terms of performance how would removing them effect it?

[centralcoaster33]

If you can use a computer to change how it responds to the secondary O2 sensors, you might be able to find 2-3 horsepower more by gutting your cats. That isn't really a noticeable amount in such a heavy vehicle. If you don't tune the computer, I'm pretty sure it will just run a bit rich because the computer changes the A/F ratio to operate on the safe side of things since it doesn't get the readings it expects. So, no horsepower gains and less gas mileage (more fuel consumption).

By the way, those 2 or 3 extra horses are only when you are in higher RPMs and wide open throttle, so you're gonna have to floor it to use or notice them. Also, unless your floor it now, you don't know what all your horsepower feels like, so you won't notice any changes (hopefully that makes sense).

[Qxx4]

Thanks man that was quite informative

[centralcoaster33]

Sure thing. I was thinking about it more last night. I believe there is a way to change the signal from the O2 sensors if you take the cats out. I mean, besides reprogramming the ecu to work with the new signal measurement from regular O2 sensors, you can get a dummy sensor that sends a fake signal to the ECU. Then the car would run fine with no check engine light. The exhaust would smell more, because it's not getting converted, and it would be a bit louder as I said before. You would not be able to pass any inspections, if you have them over there.

But, I really do not recommend it. You would be running full exhaust pollution to the air and your gains are very small (just a couple of horsepower, some have even said they noticed nothing and those people did it to V8 engines). And as I said, horsepower gains are higher up in the RPMS (see a dyno chart). It's not a good trade off. If you bought an intake system, some exhaust headers or even a cat back exhaust, you could gain more horsepower and not have to worry about pollution.