I am not sure if this is the section to post this, I hope it is and I apologize if it is not. I am a new member and this is my first thread.
I recently started doing the recommended mods in a 2009 H3 3.7L I5:
Air Doc, Ported and Polished Throttle Body, High Flow Air Filter and PCM Tune from PCM of NC.
Needless to say, the performance increase was very noticeable, specially the throttle body response. After that I installed a Gibson Cat Back Dual Exhaust (2.5 inch pipe) and noticed that the throttle response worsened quite a bit, the power seems to be there but it seems to be a little less, comparable to what it was stock before I did the mods. I am going to send the PCM for another tune but I was hoping to do the efan first then do the tune. I am not sure if it is a tune issue. BTW, I am not getting any codes and engine runs without a hiccup except for the reduced throttle response and reduced acceleration. Any ideas or recommendations?

 

P.S.: I also cranked the torsion bars up to 23 inches between the center of the hub and the front fender lip, at the same time I did the exhaust.

 

My '07 is still STOCK O.E.M., I get 9.0 sec.; 0-60.

 

Welcome.

Adding a Cat Back to what you already did will make a miniscule change. I would expect you could not detect it +/- with a butt dyno. If you just added the Cat Back, keep in mind there will be a break in period so to speak. Time for your PCM to learn what it can, and time for tooling oils and weld flash to cook off. The re-tune is a good idea after the Efan.

Again, I would not expect much of a difference with an I5, but your Gibson is a man made part, there could be a minor obstruction or inconsistency causing an issue?????

Let us know where it goes.

 

My '21 C8 Corvette is still STOCK O.E.M., I get 2.8 sec.; 0-60.

 

My '07 H3 has 5X the cargo space.

 

You Sir, maybe correct. After 100 miles or so, the acceleration has improved substantially although the throttle response is still the same. I was under the impression that throttle response would improve with the cat back. Maybe it will improve later on or I need to have the PCM retuned.... This was measured with a chrono and the good ol butt dyno. Ty fo the advice.