Re: exhaust without cats
The PID (Proportional/Integral/Differential) control system is always going to swing lean and rich above and below stoichiometric ratio. The cats absorb the unburned hydrocarbons during the rich swings and burns them off in the cats when the excess oxygen is present during the lean swings. When cats are eliminated, there is nothing to catalyze the unburned hydrocarbons produced during the closed loop rich swings. Unless you are willing to run open loop full time or are willing to tweak the O2 crossover point so that you always run on the lean side, a car without cats will always have an unburned fuel smell that is obvious to all other vehicles in your vicinity (think old school pickup trucks thats you have pulled up behind in traffic that have carb problems, you know, the ones that burn your eyes.) The latest technology cats will clean up your emissions with minimal (think 1%) HP loss. Rant over!
Jep
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