[Sirrotica]

You could certainly try experimenting with restrictor sizes to help, it may make a difference if you have steam pockets. If you have enough pressure as the system is, likely you'll see little difference.

Having run on circle tracks for much longer durations, the 3 changes I made to my cars were to increase the coolant capacity, run the A/C small pulley on the water pump, and run a 6 blade RV composite fan blade with nearly 90 degrees of pitch.

Pic of fan blade:



This took the temps from an engine killing 250 degrees, down to 180 degrees running for 20 laps in high temp, high humidity.

Closed course racing is the absolute worst case scenario for a underperforming cooling system. You'll find out in a couple of minutes if you need to upgrade your system.

One other thing is to be sure you have the GM designed, cast waterpump impeller. The tin cheap aftermarket impellers do not move the necessary amounts of water because they are inefficient, as well as aerate the coolant at high RPM. They also do not build necessary pressure to eliminate the steam pockets.

If you've ever been around a circle track after a feature race, you'll see some crews dumping water over the radiator as the throttle is held at about 3000 RPM. As Eric has said at WOT you're putting 10 times the heat into that cast iron heat sink engine. The water splashing over the radiator fins, and misting over the engine cools the cast iron down in a matter of seconds. An engine stores a lot of BTU energy after a full throttle run.