I own a 99 996 with the following modifications. Fabspeed exhaust, short shifter, Fabspeed headers and stock cats. Also have stock air box with a k&N filter along with the red tube that connects to the airbox and throttle body. I have people telling me that i need to "Chip or Recalibrate the onboard computer" i have had other people tell me to bore the throttle body and that the onboard diagnostics will enrichen the fuel mixture without having to buy a chip upgrade. Any help would be much appreciated.

Doug

 

I would chip the car. The on board computer has limitations to how much it can enrichen the mixture, it need to be reprogramed. just my .02

 

I had a similar setup with modified airbox, headers & exhaust, and noticed very little difference in hp gain,. I then got the ECU upgrade and noticed quite a bit more kick. I really think the ECU is needed to fully utilize the mods. I would not do the TB though, as I have heard very little to no gain from that.