So I was out racing with a buddy tonight. Anyways, now my car just seems to fall on its face at wot. Since I have a cutout, you can definately hear it in the exhaust. It almost sounds has if its backfireing. Any help to solve this problem would be greatly appreciated. Thanks

 

I assume you have o2 sensors as well as cats.
Make sure that there is nothing in your lid, filter, intake. ie: walmart bag.
Aftermarket cam?
check your other sensors under the hood.

 

The car is basically stock except for the lid and cutout and a racetronix fuel pump. I just took it for a ride and the car is acting up real bad now. Now you can actually hear like a hiccup in the exhaust at Idle and it gets worse when you give it gas. At wot, the best I can explain it is that it flutters and just does not have the power there.

 

SES light? if so, what codes?

K&N filter? Have you recently recharged it? if so, make sure the MAF elements are clean

also check all your wiring around the headers/exhuast manifolds. O2 sensor wires tend to melt there.