I have a 1999 454ci K2500 Suburban and I tow a 7,5000-pound trailer. Combined weight is 15,000 pounds. I added a supercharger with 5 psi to keep up with the diesels and added midlength headers as well as a MagnaFlow exhaust. I also doubled the factory secondary trans cooler size. I added a 1,000hp radiator package from BeCool. It’s basically a stock aluminum radiator with aluminum tanks instead of plastic, but you ditch the mechanical fan and add two 16-inch electric fans. The fans are rated somewhere around 1,925 cfm each. What was (is) the cfm rating of my mechanical fan? Are these fans really going to support about 400 hp pulling 15,000 pounds up a 4 percent grade at 65 mph?
You don’t usually see cfm ratings with mechanical fans because there are too many variables, especially in regard to a clutch fan. Because a mechanical fan’s rotation depends on engine rpm, the cfm (cubic feet per minute) of the fan is constantly changing. A mechanical clutch only increases the variables, and some mechanical clutch fans are even designed to change pitch with rotation speed to increase or decrease air movement. Most electric fans, on the other hand, have a fixed speed and fixed blade pitch, so their capacity for moving air is more or less constant, and therefore accurate cfm numbers are available.
It sounds like you’ve made some wise cooling upgrades to keep up with the added power and heat of the supercharger, and we’ve always been big fans (pun intended) of Be Cool (becool.com) and its direct-fit line of radiators. The company offers the radiator as a standalone upgrade or as a combo with a radiator and dual electric fans. The dual electric fan option should be able to keep up with your supercharged big-block. That said, we’re more partial to mechanical fans than electric ones. They tend to be more reliable, and they are less taxing on the vehicle’s electrical system. Though your stock alternator should be able to keep up with a pair of electric fans, if you’ve added a bunch of other power-hungry accessories, like a winch or a big sound system, then you could end up with some charging problems.
If we were in your shoes, we’d try the radiator first and make certain that everything with the mechanical fan system is up to par. Make sure the fan clutch is functioning like it should be and that the shroud is in place. Note that a fan shroud is a really important part of a mechanical fan system, and it must be present in order for the fan to do its job. Once inspected and up to snuff, our best advice is to try it and see. We’d be willing to bet the mechanical fan will work just fine with the added efficiency of the aluminum radiator, but if it still struggles to keep things cool, you can always add Be Cool’s dual electric fans later. You could also consider adding a single pusher electric fan on the front side of the radiator to assist the mechanical fan on those long grades.