Like many things in racing, keeping your engine cool is a tricky taskwedged between making sure you have enough airflow through your radiatorto keep the coolant within the proper range and taping off the grilleopening to increase downforce and reduce drag. When you boil it down toits most basic precepts, it's about consistency (and saving yourself abuck in avoidable engine repairs) versus outright speed.

As a rule, you never want to give up any more grille area in the frontof the car than necessary. Taping over the grille is one of the few waysyou can improve aerodynamic downforce and also reduce drag on a racecar. The best way to keep the smallest grille opening is to build themost efficient cooling system possible. That doesn't necessarily meanyou can simply install a larger radiator, because if you cannot supply asteady, cool flow of air across every inch of the radiator's surfacearea, you are wasting its capacity.

The Box

One of the worst things you can do is install your radiator in your racecar without a radiator box to guide air through it. Even though you maybe able to see through it, a radiator is still an obstruction, and mostof the air will simply flow around it instead of through it. The firstjob of a good radiator box is to ensure that all of the air entering thegrille also passes through the radiator. The second job of a goodradiator box is to distribute the flow of air as evenly as possible overthe entire surface of the radiator.

Consider that a radiator may be as large as 24 to 32 inches wide and 19inches tall. Unless you are driving a tractor-trailer truck, there is noway your grille is that large. Air that passes through the grille areawill continue in a straight line unless it is forced to do otherwise.So, unless you can influence the air that made its way through thegrille to spread out before reaching the radiator, you are wastingsurface area.

Thankfully, air predictably follows a set of rules that makes thispossible. Just like flowing water, moving air will attach itself to andfollow a surface as long as the path is gently curved. If, however,after attaching itself to a surface, moving air meets a sharp corner, itwill detach itself from that surface. By using curves instead of sharpbreaks to form the floor and roof of your radiator box, you can helpinfluence the air to fill the entire space. Making the radiator box asdeep as possible by moving the radiator back as far as you can alsohelps. Finally, make sure the top and bottom of your radiator box meetsthe radiator at right angles to the face of the radiator. This helpsensure the air traveling through the box flows directly into theradiator, not at some odd angle.

Eliminating the Grille

If you are racing on a higher speed track, Rodney Brennen of AFCO RacingProducts says you may want to consider doing away with the grilleopening completely. "Some race teams will attempt to run the nose closedand pull air from underneath the nose panel to supply the radiator," hesays. "This is one of the reasons we have seen most professional racersgo to a double-pass radiator. A double-pass radiator allows for a moreefficient cooling system utilizing the same given core area and airflowby first passing the coolant over the top half of the radiator and thenthe bottom half in the opposite direction, allowing the radiator todissipate heat twice from the coolant. All of our double-pass radiatorsare manufactured utilizing a 360-degree welded baffle. By doing this, weeffectively split the radiator into two sections and eliminate thepossibility of any bypass occurring from the top tank to the bottomtank. Typical results are a temperature drop of 10 to 15 degrees,although more is not uncommon." If you try this system, a strongradiator fan, either electrically or mechanically driven, is an absolutenecessity.

Fans and Shrouds

If the option is available to you, an electric radiator fan is almostalways the preferred option over a mechanical fan that is driven off thewater pump pulley. This is mainly because the mechanical fan drawshorsepower directly from the engine--horsepower that otherwise would besent to the rear wheels. An electric radiator fan, however, provides itsown motor and doesn't use any power from the engine except for extraloading on the alternator.

Lisa Chissus of Flex-a-lite says testing has shown that when using anelectric fan, it is always better to pull the air through the radiatorwith the fan mounted behind the unit than to push the air through withthe fan mounted in front. This is because once the car is up to speed,the greatest percentage of air flowing to the radiator will come fromthe car's movement. Putting a pusher fan in front of the radiator blocksthe incoming air from getting where it needs to go--through the radiatorcore. Chissus recommends always using an electric fan with a built-inshroud, as this greatly increases the fan's effectiveness at pulling airthrough the radiator.

In some cases, rules may require a mechanical fan, or you may simplyneed the extra pulling power of a larger mechanical fan. If you do gothis route, Chris Paulson of C&R Racing Radiators says you should neverunderestimate the importance of a well-constructed fan shroud. "If youdon't have a shroud that extends all the way past the fan, you won'tpull much air through the radiator," he says. "The fan will just pullair from the area of least resistance, which means most of the work thefan does will simply be moving air around inside the enginecompartment."

When you build your radiator shroud, remember the rules of airflow.Create smooth transitions from the radiator face all the way to the fanto allow the air to move as easily as possible. You don't want to buildin corners that can create dead zones. Also, try to seal the end of theshroud within an inch or two of the fan. This will ensure the fan iscapable of creating a negative pressure area inside the shroud so thatthe high-pressure air on the other side of the radiator will try to pushits way through and fill the void. But you also don't want the metalshroud to be too close to the fan in case things get knocked around abit in the event of contact with another car or the wall.

Hopefully, if you follow these tips, you will be able to close off moreof your radiator grille than ever before. The results should be improvedperformance thanks to reduced drag and added front downforce. Justremember that there are many other factors that can alter theeffectiveness of your engine's cooling system--namely the outside airtemperature. Whenever you are racing, always keep an eye on the watertemp gauge. As the night progresses and the temperature drops, you maybe able to put additional tape on the grille. Just don't push your luckand try to stay too close to that magical 220-degree F mark. Allowyourself a safety buffer in case you pick up a piece of trash on thegrille or wrinkle some sheetmetal that cuts off airflow to the radiator.

The Curves Have It

Flowing air has mass and reacts in predictable ways. Aerodynamiciststake advantage of air's properties with the help of multi-million dollarwind tunnels and advanced computer modeling, but to get more flow toyour radiator all you need is to understand a few simple concepts. Airwill cling to most surfaces just like water (stick your finger under afaucet of running water for a good illustration). It will follow a curvebut separate from the surface if it hits an angle. A radiator box with aflat top that angles down from the top of the radiator to the top of thegrille does little good at getting air to cool the top of theradiator--incoming air simply breaks away at the angle where the grilleand radiator box meet and keeps moving straight ahead (see IllustrationA). But air will follow a top panel that meets the incoming air at thesame angle it is traveling and then gently slopes up to the level of thetop of the radiator. Additionally, you can create even more flow byusing the top and bottom panels to create a venturi and increase airspeed in the radiator box. It's the same principle as what's going on inthe carburetor throat (see Illustration B).

AFCO Racing Products
P.O. Box 548
IN  47601
C&R Racing Radiators