I have just finished a 408/351 stroker, I was concerned about over heating from the get-go. Prior to the upgrade I had a 351W and could just about keep it from overheating in traffic by keeping the RPM's up. I assumed therefore that at idle the water pump was not pumping enough at low RPM, I changed to an electric water pump. The new motor makes 500HP+ and is overheating, (I have only got 20 min on the motor). I bought a shop fan from Home Depot ($99) and with the Fan infront of the car the I could hold the temp at 190. My conclusion was to upgrade the electric fans, I just finished installing dual fans (Jegs) and tomorrow I will try and see if it overheats, I will let you know. I will also note that when running at speed 80+ mph the temp would drop to 170, from which I concluded the radiator was big enough. I am not going to take the car on the road until I feel confident about the overheating at idle. I have a FAST ECU and need to tweek the parameters before I take it on the road and I want to feel comfortable I can do that with the need for the shop fan.
BTW I am running the electric water pump all the time and do not use a thermostat, I also have an
oil cooler an big 9 quart Canton Pan.