I think the conversion to be concerned about is the changing of carbon monoxide into carbon dioxide, which will essentially 'consume' free oxygen pairs in the exhaust gases. That would result in AFR readings that look leaner than they actually are. But if it only nets a 0.3 deviation in AFR, then it is likely something I can deal with. Anybody who still has cats will probably get a more conservative tune, anyway.

 

Good info,

So would you think there would be less discrepency in reading say if you had hi flow cats?

 

There is nothing in a cat that removes or converts CO. CO in your exhaust is a symptom of inefficient combustion. The amount of unburned hydrocarbons in exhaust is miniscule in comparison to the amount of fuel burnt during normal combustion. That is why burning them in the cat only uses a minimal amount of the oxygen that is available in the exhaust.