I will take you a bet that if you run a mildly modified 325 E30 over 100 mph (pleny of airflow) for over 20 minutes, you will see it overheating !
Of course this is in our balmy temperatures where it hardly drops under 100 F in summer
Anybody who builds cooling systems knows that you wan more liquid capacity in the radiator
If possibile increase the frontal surface area, but try not to add another core.
Thicker can block airflow
But this is hadly of refference for somebody racing short distances in a cool climate

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