No not the animals.
Apparently if i remove both cats on my car and put the second lambda sensor into a sleeve so it is just measuring fresh air, i can get a pretty big
gain in power (about 40hp) and still get through emmisions (its a 97 car).
Im only asking 'cos it sounds like a pretty straight forward job to just replace the cats with straight through pipes and would be worth it for
that sort of power gain 
More bang for buck must be a good thing??
You would be better to put a resistor in place of the lambda sensor? Not sure about passing emmisions tho??
What engine is that on? a 40bhp gain sounds like a hell of a lot.. even on a turbo'd car i wouldnt expect that much of a gain by just removing the cats
Putting the sensor in fresh air will make the ecu think the engine is running very lean and it'll chuck in more fuel (up to it's fuel-trim
limit) to compensate. I would think it unlikely it'll run efficiently or pass emissions in that state.
It might be that with a reading that far out the ECU will assume a failed O2 sensor and revert to fixed fuelling, but you might as well unplug the
sensor to achieve the same thing.
The lambda is there for a reason.
Putting it in fresh air will just make the car run rich all the time which does mean more power up to a point (peak power is 12.5AFR ish) but anything
more and you loose power.
Oh and your economy will plummet to. Like driving everywhere with your foot on the floor!
David
if its a 97 car doesnt it need a cat anyway?
i thought it was pre 95 that didnt need them?
quote:
Originally posted by Miks15
if its a 97 car doesnt it need a cat anyway?
i thought it was pre 95 that didnt need them?
On any vehicle I have encountered the second (post cat) lambda sensor has no effect on mixture it is fitted purely to monitor the efficency of
the upstream sensor and cat..
When everything is working properly and engine running closed loop the upstream sensor should have continously flickering output and if the cat is
working the downstream sensor a fairly steady output.
As soon as the engine has fully warmed up and gone closed loop The ecu compares the reading of the upstream and downstream sensors if the readings are
similar it knows something is wrong and flags up a fault code.
It is possible if the ECU firmware is sloppily written that removing the downstream sensor from the exhaust flow stops the the ECU from detecting the
cat is not working (ie missing ! ) and stops the fault code being flagged up.
You can remove the cat, but not the sensors which will give a power gain, not 40hp unless your CAT is blocked.
It will also pass an MOT on emmissions without a cat, but better to leave a cat looking box in its place to save queries.
CAT's are mandatory after 93 if memory serves me well, I had a XJS that was just pre cat on a 'K' plate so removed it without any
issues beyond the occasional weak mixture when flooring it.
Regards Mark