Proper Thermosts temp for 318

On a street engine I wouldn't run anything cooler than a 180 and my preference is a 195. Engines that come up to temp quickly last longer, use less fuel, and stay cleaner inside. Nothing is gained by running the engine cooler. As others have mentioned, some of the low cost 54mm thermostats out there don't flow particularly well. There are plenty of high quality thermostats out there that cost two or three times as much as a cheap one. Spend the extra $3-6 and buy a good one.