I have a 4 bolt 350 very mild...no mods. I'm running it with a ford flat head radiator. I have a 195 thermo with an eletric fan and an auto switch which turns on at 185......my temp gets up to 210-212 before I shut it down. I'm still working on my truck so I have not had it on the street or in traffic so this has been in my yard at idle for a duration of 15 to 20 min at a time..