i put a custom cat back on my car yesterday to eliminate the catalytic converter.didnt touch the downpipe so all o2 sensors are where they should be..i noticed a big drop in gas milage... i have a safc installed so what is a good setting to set the high and low throttle settings across the board...i just put -4% to see if it helps...imma eventually get a wideband but please give some advice someone

 

seriously no one can answer this?

 

Well, i'm not expert but if the custom cat is bigger then specs, let's say 3 inches instead of 2.5 , then i guess it's normal, you're asking more on the engine.
A bit more info would be useful

 

Its a 2.5 inch cat back with a 3 inch resonator. I only eliminated the first catalytic converter closest to the back that doesn't have the O2 censor. And when I say decrease gas mileage, I mean significantly like 15 miles to the gallon. How low can I go for the high and low throttle before it's unsafe because I am already doing -4%.

 

Just the catalytic converter? Off the top of my head, I can think of possibly exhaust leaks, or maybe a bad catalytic?

I am not sure what else the exhaust system could do that causes that much of a drop. Unless its clogged or something.

 

i figured it out...when i put the cat on, my safc was probably over riding the original fuel output and since my exhaust is now completely open i had to restrict fuel so i set the fuel output at hi and low across the board at-6%...a/f ratio is perfect now and im getting way better gas mileage then i was even when i had the original exhaust on...thanx for the feedback everyone