I have K&N drop in, stock manifolds, Magnaflow Y-pipe with hi-flo cat, and 2.25 straight pipe side exit before rear axle.

1. What are the chances my engine is running lean?
2. Does the ECM adjust to the increase of air flow thru the system?

 

zero.

 

If your check engine light is not on then the air/fuel mix is fine. You O2 sensor tells the computer how to adjust the fuel.

 

Thanks fellas, I am coming from the motorcycle world. If you change the air flow volume in bike, you usually need to retune the ECM to keep it from running lean.

You guys think adding a glasspack or muffler on my system give more low end torque?

 

Yeah for some reason the motorcycle world is hesitant to keep up. They use preset fuel mapping that cars dropped in the 80's for the most part. I was surprised to find out my 2014 vstar worked that way. That's why tree huggers are pushing for emissions laws on bikes. From a technology perspective its just silly that we are running engines near the size of a small car and only get around 100 HP when they are getting over 300 in some cases. Not to mention the emissions on a bike are closer to that of a new truck. As much as I don't want to pay the fees and have the inspections I would love the manufactures to step up design a bit.
For exhaust a chambered muffler technically gives you the best torque. But in all reality you are talking small numbers. It really comes down to sound preference as long as the mufflers are free flowing. Stock mufflers are a choke point designed to be cheap and quiet.