If your racing, why the hell would you need an O2 sensor anyways? do straight exhaust 2.25inch. Put a O2 defouler where the o2 sensor is supposed to be and screw the o2 sensor into the defouler. They are like 40 bucks.
Make sure your car is receiving adequate spark. Use a multimeter and test for resistance on your wires, test your relays and make sure your battery is well grounded and not corroded at the chassis.
Also, your throttle position sensor and your engine coolant sensor both work together. ECT detects your engine coolant temp and adjusts your fuel ratio in sync with your TPS sensor.
These engines were not designed for racing, so its possible you need to do some tweaking to the ECU so you can run the car hard for very long periods. I would start with whats easier and cheaper, then work my way down.