Join Date: Oct 2006
Location: Staten Island, NYC
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Re: CEL & Catalyst Removal
first off, let me start by saying that the knowledge i have about o2 sensors and their effects on performance are from my personal experiences with my G35, and the members of G35driver.com and My350z.com, 2 online forums like this one with LOTs of expert members......
all things being equal (i.e. if the computer doesn't interfere) you will gain power by freeing up the extra exhaust flow
most newer cars use 2 sets of o2 sensors...
primaries which are in the headers (before the cats) and secondaries, which are after the cats.
the primaries are the wideband o2 sensors that the computer uses to make adjustments to the AFR/timing/tune etc. basically those are the sensors that give continuous feedback to the ECU and control the running of the motor.
the secondaries are ONLY there to tell the computer that the stock cats are doing their job... that is the only information they pass on to the ECU (and on some cars they make small adjustments to the long term fuel trims, nothing noticeable or necessary)
problem is, when you DO remove the cat, the secondaries tell the ECU that it's emissions gear isn't working, and it puts an electronic chokehold on your power.
tricking the secondary o2 sensors into thinking that the cats are still functional (by using some form of "sim box") should not in any way harm the motor or anything on the car, and will allow you to realize the gains you should be getting by removing the OEM cats. a sim box will simply tell the ECU, "hey guy, no problem down here, your restrictive OEM cats are still A-ok!" meanwhile you're running open pipes and gaining power
the issue has to do with phasing between the voltage readings on the primary and secondary o2 sensors in each exhaust tube. for example...
if the primary sees: ~~~/\~~~/\~~~/\~~~
and the secondary sees: ~~~/\~~~/\~~~/\~~~
then the computer knows that there is nothing in between altering the exhaust gasses (no cat converter present). a sim box might alter the second signal to show ~~~^~~~^~~~ which is less voltage fluctuation, which makes the computer think the cats are stil there
have i confused anybody yet?