Slow Crank, No Start When Warm

My race car is wired like that, the solenoid is jumped at the starter, and had a Ford style solenoid back near the battery. That way the battery cable to the starter is only hot when the engine is cranking. Depends on how the rest of the car is wired. Sometimes the factory starter relay is used for a voltage junction. I would increase the positive and negative cable sizes, and check for voltage drop. And possibly try another starter. And I also like to get the engine turning over before turning the ignition switch on, seems to help when hot