Let's look at John's car as an example. John runs a four-core system from ICE which may sound like overkill but in USAR Pro Cup racing it's almost a neccessity. On a typical weekend John will turn 300-400 laps on tracks 5/8-mile and bigger. A double-pass system would be inadequate for this environment. But the ICE four-pass system keeps the water temperature at an acceptable level even when he runs tape on the nose, a practice asphalt racers use to add aerodynamic downforce to their cars.
Typical short track racers don't need a four-pass system. They will find single- and double-pass systems will work fine for most situations. But which one to choose? There are advantages to both.
Pros & Cons
The advantage to running a single-pass system is that it's about $30 cheaper than a double-pass.
The down side to a single-pass is that it's less restrictive than a double-pass. And that reduced restriction means that the fluid is going to run through the entire cooling system at a quicker rate.
The other down side to a single-pass is that it's not as efficient as a double-pass. Faster flowing air may not have as much time to pick up heat from the tubes. And that's the point of the radiator in the first place, to dissipate heat. Also since the fluid also runs through the radiator a single time, the air passing through only gets one chance to pull heat from the fluid. If the air only "sees" the fluid one time and the air is passing that fluid at a fast rate of speed, it may not be maximizing the heat extraction. But again, much of this depends on the application. Our Project Dirt Late Model has a single-pass C&R radiator that works perfectly on the 3/8-mile dirt track (Ocala Speedway) that we run weekly.
There's virtually no weight savings between a single- or double-pass system because a double-pass radiator is basically a single-pass radiator with a baffle inserted into it that directs the flow of water through the radiator a second time. They're the same size and virtually the same weight. But where the double-pass shines is in its ability to cool your engine.
"A double-pass radiator will increase your cooling efficiency anywhere from 5-10 percent based on the application," says Bridges.
VP's Cool Down is a cooling...
VP's Cool Down is a cooling system additive that reduces cooling system operating temperatures by up to 50 degrees. It reduces coolant surface tension, allowing better laminar coolant flow for better heat transfer.
But what about the additional restriction provided by a double-pass? "Today's big water pumps which flow so much more water basically offset the additional restriction you'll find going to a double-pass," says Bridges.
There's another benefit. Say for performance reasons you want to run your motor a little leaner. Any time you lean out the engine, it's going to run warmer; switching to a double-pass gives you that extra needed cooling efficiency at an increased cost of only $30. Finally, the double-pass will move your inlet and outlet hoses to the same side of the radiator, making for a cleaner engine compartment.
The decision of what type of radiator and associated cooling system your race car needs should be based on your series, motor size, and the highest temps you'll see during the summer months.
Wrapping It Up
Ultimately, you need to speak to your engine builder and your chosen radiator manufacturer to ensure that you get the correct cooling system for your race car. Companies like C&R, Afco, ICE, and others are more than happy to help you select the right radiator for your application. However, there are a number of items that you need to pay attention to regardless of the type or make of radiator.
The type of water you're putting into your radiator is important as well. In a passenger vehicle we use anti-freeze, whose active ingredient is Ethylene glycol, nasty stuff. When added to water, anti-freeze drops its freezing point well below the typical 32 degrees F. Obviously race cars don't need anti-freeze, unless you're ice racing in Alaska, but can you do better than just plain tap water?