Efficiency
Every part of a radiator is designed with the singular purpose of dissipating the heat collected by the water as it flows through the motor. How efficient a radiator accomplishes this task comes down to two specific types of "flow," that being water and air.

Water Flow - Water, or fluid as we have been calling it, flows into a header or large open cavity on one side of the radiator where it then passes through the aluminum tubes before it collects into a header on the other side. This flow of water through your radiator can be influenced a number of ways including through the use of restrictors, the size of the water pump and related pulley system, and the aforementioned inclusion of a turbulator.

Pumps & Pulleys - One of the biggest influences on how efficient your radiator functions is the size of the pulley on the water pump. If the pulley is too big it won't push enough water through the water jacket and radiator to effectively cool the motor. Conversely, if your pulley is too small, water will be pushed through the system so fast it won't have enough time to collect heat from the motor or dissipate that collected heat.

Compounding this problem is the pulley system. Water pumps in many circle track engines are driven off of the crankshaft via a pulley system. If the pulley system doesn't spin the pump fast enough you won't push enough water through the motor/radiator.

Case in point, a friend of the magazine who runs a Dirt Late Model recently had his engine rebuilt. During the rebuild, his engine builder suggested an exotic NASCAR Cup-style pulley system. The builder said the smaller V-belt design of the system would free up horsepower. Now keep in mind that this 550hp motor never had an overheating problem and consistently ran in the 180-190 degree range. It also had a brand-new radiator recently installed. From the first race with the new pulley system, the motor always ran above 220 and would peg the temperature gauge when our racer friend shut it off.

Here's the problem. The smaller pulleys were mismatched to the water pump and ultimately the engine application. They weren't designed for a 5,500-rpm 550hp motor with a stock-style pump and spun the pump too fast, pushing the water too quickly through the cooling system.

Restrictors - In addition to water pumps and pulleys, restrictors are commonly used to regulate the flow of water through the radiator. They're just what their name implies and look like a small funnel engineered to cut down or restrict the flow of water. Usually mounted in the lower radiator hose at the radiator outlet neck, restrictors come in various diameters. Choosing to run a restrictor is a matter of matching it to your system.

"It really depends on the application," says C&R's David Bridges. "With today's water pumps flowing at such high rates, the radiator itself is your biggest restriction and a double-pass is more restrictive than a single-pass."

Bridges says when changing from a double-pass to a single-pass radiator you want to begin with no restriction and then gradually add restriction based on restrictor size until you get the temperatures where you want them. "We always recommend running your water pump at a 1:1 ratio." A 1:1 ratio means that the diameter of your crankshaft pulley is the same as the pulley on the water pump.

Airflow - Like water flow, there are a number of items that affect airflow through the radiator such as fin count, the number of passes, the design of the core, and whether or not it has a shroud.

Cores - Racing radiators come in several different configurations including one-, two-, three-, or four-core/pass systems. This means that once the fluid enters the radiator via the inlet it will make that number of passes through the radiator before it exits back into the engine via the outlet. The most popular short track configurations are one- and two-pass radiators.