Not sure I agree with you unless data is provided. In fact, the target emissions and stochiometric ratios of the stock car may not be optimal for power but more of a compromise for emissions. In addition, and I have verified this with my own eyes, the A/F ratios get thrown out of whack a bit when you either remove completely or replace the primaries with HFC cats. We monitored the ratios on the dyno. We then tuned the car. Then shut of CEL and did more dynos. Max power was with the CEL OFF. There is more power to be gained with the HFC cats and no CEL than the stock cats and leaving the cats in ready mode.
Just clarifying.....
Quote:
Originally Posted by Lemans_Blue_M
They are running a little worse...they just don't realize it. 
The post cat 02 sensors are simply used to fine tune the AFR's, not directly control them. That job is reserved for the pre-cat 02 sensors.
Here is where confusion comes in...
Many BMW owners think the post-cat 02 sensors don't play a role at all, because once they are turned off...they can't tell the difference with their "butt dyno". 
A word to the wise...
Butt dynos are notoriously unreliable. lol... 
When you tell them the post-cat sensors actually do play a role in the ECU tuning they can believe it because if it did...they would FEEL the difference in power.
Well here's why they don't...
The pre-cat 02 sensor data controls about 99% of the overall ECU tuning functionality.
The post-cat 02 sensors control approx. 1% of the ECU tuning functionality.
That's WHY the majority of the guys who shut off the post-cat 02 sensors think they don't have any effect.
1% of 414hp is...4.1 hp.
4.1 flywheel hp = approx. 3 rwhp |