Push Me, Pull Me
Norman Neal; via CarCraft.com: I’m pretty sure you’ve run a tech article in the past about cooling fans. I’ve got a ‘49 Chevy pickup with a healthy 496 big-block Chevy and an aluminum radiator using a pull-type electric fan. I’ve never had a heat issue with it. With my it’s-not-broke-but-I’m-going-to-fix-it-anyway approach, I’m going to put a 6-71 huffer on it and will need to change the fan to a pusher mounted to the front of the radiator. I’m looking for an answer that will explain the exact difference in effectiveness between the pusher and the puller mountings.
Some fans can be converted from a puller to a pusher by not only switching the leads on th
Jeff Smith: We asked a Ford cooling-system engineer this exact question several years ago, and he said that a pull-style fan is generally about 10 percent more efficient than a pusher fan. While that’s a very generic answer, it’s clear that using a puller-style fan will move more air than the same-size pusher fan. However, you might not be able to just remount the fan in front, since most fans are designed specifically as either pushers or pullers (most fan companies will specify if the fan can be used in either direction). This means if you reposition a puller as a pusher and then just switch the leads on the fan, the setup may result in less than favorable results. We spoke with Dave Heutmaker at Flex-a-lite, and he says that with most Flex-a-lite fans, you can remove the fan from the electric motor, flip it over, and then reverse the leads to the electric motor to turn the fan into a pusher. When mounting the fan to the front of the radiator, you can improve performance by placing the fan very close to the radiator and carefully sealing the area around the radiator core to prevent air from bypassing the radiator core.
In terms of choosing an electric fan, size matters. A pair of smaller-diameter fans will do a better job of moving air than one large fan because the two can cover more area. Twin-fan packages are also often mounted in an offset pattern to squeeze a pair of slightly larger blades. It’s not accurate to use amperage draw as an indicator of fan efficiency, as electric motor quality can vary wildly. A more efficient motor will pull fewer amps than its less-efficient cousin. Fan design also makes a difference. Straight-blade fans are generally noisier and will move more air than a curved blade, but Heutmaker says current S-blade designs are often more efficient than even the straight blades, so that might be worth additional consideration.
Radiator thickness also affects fan performance. Most fan companies don’t recommend using a pusher assembly on a four-core radiator because the added core thickness makes it difficult for air to push through. This is a tough enough job for a puller fan.
Beyond the question of proper positioning, it’s also important that the fans be wired professionally. Each electric fan should use a dedicated relay. Relays allow you to use a light-duty switch to control high-current-draw fans. We’ve worked with the guys at Hollister Road, a small company that makes a nice wiring package that combines relays, circuit breakers, and a wiring harness to control a pair of fans. The switch is set up to turn the fans on at 210 degrees and off at 185 degrees. You can also order an additional switch so you can control the first fan to come on at 185 and the second fan to come on at 210 degrees. This would put less load on the alternator, as the second fan would only come on is when it is really needed.
For applications in which a pull fan will fit, Hollister Road also offers relay kits for giant Lincoln Mk VIII, Taurus, and T-bird fans that you can buy new for a great price. The Lincoln fan is generally found as a two-speed fan, and Hollister Road sells a relay controller that will run the two speeds in a similar method as described above. A ’95 T-bird fan can be purchased for $72 through Rock Auto, so there’s no reason to go searching through the junkyard when you can buy a new one that is this inexpensive. We covered this issue in more in detail in our Junkyard Builder story in the Nov. ’11 issue. You can also find the story online. What’s good about this fan is that it moves some serious air, perhaps even more than a pair of smaller fans. Check it out.
The Wheel Deal
Tim DiMasi; San Diego, CA: I’d given up on something until John McGann’s piece on wheel widening (Dec.’11) renewed my interest. I’ve got a white ’10 Dodge Challenger R/T with 20-inch wheels and 45-series tires. Its color and simplicity of design scream for ’60s-era steelies, Mopar dog-dish hubcaps, and 60-series tires. I figure an 18-inch-diameter wheel will do the trick. I’ve located a supplier that says it can handle an adapter to take the 5x115mm bolt pattern to the traditional Mopar 5x5-inch pattern, but this is as far as I can get. Those younger guys who missed the days of bare- bones Coronets stuffed with 383s and Max Wedges think I’m nuts. Maybe I am, but I still want my steelies. Whatchathink?
Jeff Smith: I discussed this with staffer McGann, and he remembered seeing steel space-saver wheels in some late-model Charger LX-platform cars. Most spares are 17 inches, but a few are 18-inch wheels, depending the brake size of the car they go with. He did a search and found one on eBay that mounts a tiny 135/90-17 tire for the “buy now” price of $95, though the highest bid at the time was only $35. We learned that this wheel has the same 5x115mm bolt pattern as your Challenger. So your next step could be to purchase four space-saver wheels. But before you make this step, take the time the measure the caliper clearance around a 17-inch wheel. The ’10 Challenger uses a 12.6-inch-diameter rotor, which pretty much eliminates using a 15-inch wheel, but you should measure caliper clearance to make sure a 17-inch wheel will fit. If it does, you can go forward on deciding the width of the new wheels. The factory rims are 9 inches wide, so that’s a great place to start. Then you can have a shop like Pico Wheel cut the centers out of the space-saver wheels and mount them in 17-inch hoops of the proper width. Once the width is determined, you can look for a tire that is roughly the same diameter as the original Challenger tires. The stock tires on your Challenger are 245/45ZR20 Goodyear RSA tires that are tall rascals at 28.7 inches. On the Tire Rack website (TireRack.com) we found a 255/60R17 tire that is 29.1 inches tall, which is around 0.4 inch taller. This will affect your speedometer readout by about 1 to 2 percent. To make the car look right, you need a decent performance tire, so we dug a little deeper and found that General makes a Grabber UHP tire in the 255/60R17 size that has a cool, aggressive tread pattern. General recommends mounting this tire on anywhere from a 7- to 9-inch-wide wheel.
You will also need to specify the amount of backspacing you want on these custom wheels. Since the new 17-inch tires are 20 mm, 0.787 inch wider, it might be best to move the wheel inboard slightly. The best thing to do is measure the amount of clearance available with the Challenger’s current wheel and tire package. If you have more inboard than outboard clearance, add the appropriate amount of backspacing. Let’s say you have 3⁄4 inch of clearance on both the inboard and outside sides of the tire with the current wheel/tire package. Since the new tire is 3⁄4 inch wider, that’s 3⁄8 inch wider on both sides. To simplify our example, let’s assume the backspacing on the 20x9-inch factory wheel is 4.5 inches. The easy thing to do is to duplicate that with the new wheel with a zero offset. In the front, you will need to pay attention to clearance at full lock, but more than likely, it will clear as well. It would be best to compare the overall section width of the tire you choose for the new 17-inch wheels against the section width of your factory tires. While overall diameter for tires is generally consistent, we’ve seen a difference of as much 3⁄8 inch in overall width in same-size tires from different manufacturers. Section width is the measurement of the widest part of the tire when mounted on a given wheel. For example, the 255/60ZR17 General UHP Grabber tire mounted on a 7.5-inch wheel generates a 10.2-inch section width. We looked at the section width for the Goodyear, Dunlop, and Pirelli tires of the same size and they all had the same section width, but it is something that warrants attention.
Finally, space-saver wheels don’t appear to be able to mount the Mopar dog-dish hubcap. But that just means you will have to be creative. We’ve seen guys use an aluminum spacer that screws onto the stud drilled and tapped on the other end for a 10x32 panhead screw. Locate the position of this spacer to the hubcap and drill a hole in the cap, perhaps in a dark or painted area where it will be less obvious. The machine screw could be painted black to make it nearly disappear, and the hubcap would be secured.
General Tire; Fort Mill, SC; 800/847-3349; GeneralTire.com
Pico Wheel & Tire: North Hollywood, CA; 818/982-0375
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