Hole before the cat

Do I get any hp from replacing the O2 sensor with a simulator and leaving the hole open to decrease the pressure before the cat?

Well you would get some if you use the O2 sim and replace the cat with a tube. But a hole before the cat? I have seen stuff like that when the cat is really cloged and the guy did not had enough money to replace it but make a hole in front of it? To get the response you want (AKA like having a tube instead of a CAT) the hole would better be a cutout.

From before I meant towards the downpipe and headers. The hole from the o2 sensor is smaller than the cutout but with a simulator the rest is free and replaceable. Wouldn't it also make sure that I'll pass aircare? (if they don't find out about the hole!)

Well that is what I tought. The performance gain would not be really enough to justify the O2 sim cost, you would not even need an O2 sim. The O2 sim is more for cars that have the cat removed.

Holes in the exhaust generally sound like butt.

Do I get any hp from replacing the O2 sensor with a simulator and leaving the hole open to decrease the pressure before the cat?

Do you mean removing the 02 sensor that is before the cat and leaving that hole open?

I don't think your car will run without that 02 in place...and even if it does run, it won't run right. That sensor is used by the PCM to monitor the engine A/F ratio. The 02 sim is only meant to replace the 02 sensor after the cat.

If you meant the 02 sensor after the cat all that will do is make your car sound like it has a big exhaust leak - putt-putt-putt-putt-putt.

Do you mean removing the 02 sensor that is before the cat and leaving that hole open?


From before I meant towards the downpipe and headers

I think you are right he meant the front sensor. Wouldn't that throw a code right away?

Well I have the o2 sensor after the cat removed and the car runs fine so I thought it would be the same case if I had the one before the cat removed and the one after in place. Seems like the cutout might be worth the money spent. And how many HPs from a cutout? Does it matter what kind of headers u got?

NOOOOOOOOOOOOOOOOOOOOOOOOO, now I get it and is a big NOOOOOOOOOOOOOOOO, what the O2 sensor before the cat do is tell the PCM how rich or lean the mixture the car is spewing out and the one after the cat tells the PCM how good the CAT is burning harmfull gases. There is no O2 SIM for the front sensor, the only ones I have seen are for the one after the cat used only when you replace the cat with a tube for off road purposes. And these guys are correct. If you take the O2 sensors out the car would make a bogus A/F mix and highly possible the cat would not be enough to clean it to pass emission testing, your mileage would be poor, the power might go down. A car that is too rich will not really run better unless of course you add a lot of PSI to the air intake with Forced Induction and that would required you to do a lot of tunning to manually adjust the A/F and to my humble understanding the only thing you can dou outside the PCM to control that is incrementing the PSI going down the intake plenum.
And doing that without the sensors in place is like walking blind, how the heck you will know the car is not too rich or too lean?(A car that is too lean could break pistons or rings).
So No, do not do it :nono: