The car has been tuned on crome with I/H/3" R&D exhaust (no cat). It's a stock motor. Recently, I welded on a Vibrant metallic race cat along with 2 resonators to shut it up. Will this change my A/F ratio - need to be re-tuned?

 

Anything that changes air flow through the motor will change your A/F ratio.

The cat is a restriction, probably not much but some...if anything, it will go richer (same amount of fuel, less air through the motor).

 

it usually richens it up alittle so it should be fine.

 

Cool, I'm glad that's confirmed. I'll get the car on a dyno to measure the A/F and compare it to the original tuned graph

A little rich should be fine, better than leaning out. As long as it's still in a good spot. The car is my DD so I just want to make sure she's stable. Thanks

 

wow me and Xeno posted at the same time.l

 

If you have O2 feedback enabled then no, you have nothing to worry about.

 

Is that a feature available with crome? The tuner never mentioned such a thing.

 

This is not true when at WOT, or where ever your program is set to switch from closed loop to open loop.

 

If it's a MAP sensor based ECU then it will run lean when you add more air flow, i.e. larger exhaust, intake, etc. or run rich when you restrict air flow such as a cat, smaller exhaust, etc.

However I'm sure you already know this.