Ok, so I finished my 4.10 gear install and the car pulled like a mad man. I was extremely happy. I then proceeded to install my headers. Running open headers the car felt slower than it was before the gear install I came up with a number of excuses and proceeded to fab up the rest of the exhaust. After finishing I ran it again, and it seems a little better, but still way too slow. Prior to installing the gears or the exhaust I was running 14.6 with a 2.3 60' (which is 13.7 at sea level). I'm still running 14.6 with a 2.3 60'! The torque that I gained with the gears totally disappeared once I installed the headers. So, angry and distraught I ran the car with Datamaster and low and behold, 10 degree of spark retard. I don't hear any pings that would be real knocks, so I believe they're false knocks. I do have a LT4KM.

What do I do to go about fixing this? And would 10 degrees of spark retard slow the car down this much? Realistically the car should be 13 seconds no questions asked.

 

Get the PCM programmed. The headers are making more noise then the factory manifolds did so the PCM thinks its knock.

 

Annother thing to think about is if you are running open headders with 02 sensors. You will be running pretty rich. Also try an LT4 knock module to help with the spark retard.