Is your radiator clean (inside and out)? Are the fans working on high speed? Is your T-stat opening all the way?
What is the concentration of anti-freeze? Note, anti-freeze does not cool as well as water. Consider adjusting the anti-freeze concentration to 40%. Much lower and corrosion can become a problem.
If the system is working as designed, then some consideration should be given to an upgraded cooling system.
Note: increasing the coolant system pressure will give additonal head room before boilover. However, the engine is still generating more heat than the radiator is removing. I am afraid that increasing the pressure will only slightly delay the boilover while allowing to engine to run hotter than designed.
This may seam dumb. Try putting the heater on full blast. This may also allow the car to run just a little longer before overheating. Or wait until over heating is about to occur and then use this trick. It could keep you in the race.
New radiator, new T-stat, new radiator cap. I have found a Ford cap holds pressure better than a Slant cap. It doesn't overheat, the 16 psi cap just releases pressure and sprays anti-freeze over the engine during a track session. It think it is just doing what it is designed to do. I've been running at VIR. Each session is about 30 minutes. I'm hitting 125 mph + twice a lap, so it's working the motor pretty hard.
Perhaps overfilled? When the enging is working so hard, it is reasonable that the coolant will get hotter. As such, more expansion would be expected. Consider filling slightly below the "full cold" line and see if this controls the anti-freeze spray.
Frankly after it cools, this should define the fill line needed (excessive coolant already ejected).
Again, water has a better cooling ability than antifreeze. You could try 90% water and 10% antifreeze, but obviously this is not a year round solution.
Do you still have the factory black air diverter at underneath your front bumper? That actually helps push air through the radiator, so it doesn't go around underneath.
Beyond that, you could try a 3 core radiator, I believe the stock and stock replacements are only 2 core, right?
Thanks for the responses. The car has just about every bolt-on you can do. Long-tube headers, spin-tech mufflers, cold-air, throttle-body, plenum, underdrive pulleys, AC delete, Diabelo tuner. It's a stock block. Anyway. I'm running between 5000 and 6500 rpm for 30 minutes on track. A radiator upgrade is really whats needed. Since I recently replaced the stock radiator, I'm looking for a quick, cheap fix. When I've run other cars on the track the 19 psi cap has helped. I've found an aluminum reservoir that uses a standard cap. I might try that.