I set my 73 stock 400 4 barrel at 15 initial, and 35 total. It never ran so smoothly, and real nice acceleration. While on a nice short cruise on the highway, I ran the A/C. Temp went to the high range. I did the heater trick, and man, was it hot air!!. Coolant is new and full. Clutch and viscus fan are all in good-working condition. Stock 28 inch radiator. It's a Cali car, so I can't imagine this is all kosher. What are your thought? Thanks. Need it worked out for the Nats. By the way, outside temp was only 75. Thanks