I used to be a Powertrain Cooling engineer for two companies and I can tell you the shroud is 100% needed. Its a VERY big deal. Even small holes will mess things up. You'd be surprised how important it is; your fan is practically useless without it. The seals in the front and the shroud around the fan are VERYimportant.

The radiator is a very restrictive pathway for air and air will take the path of least resitance. Unless you make it the path of LEAST resistance by doing somthing like putting a fan shroud or rubber seals there (a rubber flap is more restrictive than a radiator), the air will just go around the radiator. You'd honestly be surprised. Without those seals in the front, you will barely get any airflow through the radiator. Without the fan shroud, the fan will just pull air in from behind it/on the side instead of pulling it from the other side of the radiator like it should. That means the air wont be going through the radiator.


You're better off with a stock size radiator and shroud than a bigger radiator and no shroud. You wont even need a bigger radiator to be honest, I'm surprised anyone running NA does, with the exception of heavy towers. The front end of the radiator most of the work. The futher you get towards the "out" side, the cooling it does -exponentially. Something like 80% of the cooling is done in the first half of the radiator. Its already pretty cool by the time it gets past the first half.

Just use your personal experience: what drops will get 20 degrees cooler faster? a 600degree peice of metal in 75degree air or a 100 degree peice of metal? that 600 degree peice of metal will be 580 before you can blink. It will take a while for the 100 degree peice of metal to get to 80... actually, a very long time.

For thee same reason, the hotter the incoming coolant, the better your radiator works. I've done some simulation work, and if I wasn't so lazy id bust out the heat transfer formulas; it takes a VERY large increase in coolant inlet temp to get a significant coolant outlet temp. Heat transfer like this is all based on temperature difference. Like the bar of 600 degree metal and 100 degree metal, the heat transfer between the 600 degree metal and 75 degree air will be much higher since there is a bigger temp difference (525 degrees) whereas the 100 degre metal has only a 25 degree difference. For that instant, the hot metal will be giving off heat at 21 times the rate of the the 75* bar.


Its not like "ohh it came in 1 degree hotter so it will leave 1 degree hotter." It would probobly have to come in 15 or 20 degrees hotter to leave 1 or 2 degees hotter (under normal conditions). That may not sound like a lot- but it is, especially since it cant really "build up" temperature over time. It would have to get much hotter very, very quickly. Its just hard to do because the hotter the coolant gets, the more heat the radiator can dissipate thanks to the bigger temp difference AND the hotter the coolant, the less heat it takes in from the engine (smaller temp difference).


The GM PTC tests are pretty ******* nuts. They are done in very demanding circumstances that a normal person (even you crazy ********!) wont see unless you tow in death vally or something

 

That is very useful information there and something for everyone to ponder. I appreciate it. I'll continue to run the shroud.