Originally Posted by nova gary
i have a 69 nova 350 keeps buildiing heat will run ok going down hyway but you can't drive it in town .have changed radators new pump took engine down everything is clean don't have room for a shrould even have put a 2inch 6 blade fan on .the rad is bigger then the three row but is only 2 row two i inch rows should hande 650 horse and i am pretty near stock rv cam with headers and 10.1 flat tops . thinking of reverseing my cluth fan .can anyone give me any ideas .sure would be thank full.
Typically overheating at low speeds or when stopped but idling is a pretty good sign that there is not enough air flow over the core of the radiator. Assuming you've got a large enough radiator in terms of core area which for a 350 would be about the equivalent of 30x19 inches. In copper/brass this would be a 3 or 4 tube core for aluminum 2 rows of 1 or 1-1/4 tubes. You would find that either of these types have a very similar rate of heat transfer so the coolant temps will be very similar in otherwise identical driving situations.
A shroud provides coverage of the perimeter of the core with a fan at the outlet end. When the fan is operating but the vehicle is not moving or doing so slowly the pressure inside the shroud is lower than atmospheric causing the outside air to be drawn in over the entire area of the core. Without a shroud in this condition the only air being drawn in is immediately before the fan which leaves a lot of potential heat transfer area doing little to nothing.
It really doesn't take much depth of shroud to make a big difference in temperature reduction. All that really needs to be satisfied is the perimeter of the radiator be enclosed and reasonably air tight around the edges of the front of the shroud while the fan needs to be covered by about 1/2 to 3/4 the twist depth of the blades. I've used deep baking sheets trimmed to fit the radiator and fan, built them from sheet metal, and laid up fiberglass on a skeleton of 1/4 inch hardware mesh as well as combinations of these methods to make an effective, well fitting and safe shroud. The fan end needs to be reinforced when using any of these methods as there is a lot of vibration of the shroud in this area from the fan.