Premium High Flow Water Pumps With A Racing Heritage And A Lifetime Gaurantee Cooling System Basics Performance Through Research Howard Stewart is the acknowledged leader in high performance cooling system research and development. In addition to developing our own products, Howard Stewart has continually done research and developement for other companies. Previous clients include: General Motors Ford Motor Company Chrysler Corporation Mazda Sunoco Shaver Specialties Advanced Engine Development Brayton Engineering Wesmar Racing Engines Robert Yates Racing Dart/Richard Maskins Petty Enterprises Hendrick Motorsports/Randy Dorton Our equipment, designed and built in house, includes: Water Pump Dynamometer Tests water pumps for flow, pressure, and power consumption at variable temperatures, system pressures and restrictions. The most advanced water pump dyno ever built. Fan Dynamometer Tests fans for air flow and power consumption, free flow and through various radiators at variable vehicle speeds. Wind Tunnel Tests radiators for pressure drop; air and water, and heat rejection rates at variable temperatures, water flow rates and air flow rates as related to vehicle speed and grill opening. Flow Mapping Equipment Tests engine combinations for overall flow and pressure drop. Determines the flow through every orifice in the head gasket. Basics To increase your cooling system's performance you must maximize both the water flow and the airflow. Water Pumps Howard Stewart is the only water pump manufacturer that specializes in the design and manufacturing of high performance water pumps. Installing a pump from Howard Stewart is your only assurance that you have a pump designed for your application and manufactured to exacting tolerances for trouble free performance. Pulleys Race applications  require a maximum water pump speed between 6,000 and 7,000 RPMs. Street applications require the water pump to be driven at least at crankshaft speed to as much as 35% faster. NEVER use undrive pulleys on a street vehicle. Howard Stewart's high flow water pumps consume only 2.26 horsepower at 4,000 RPMs, so any parasitic drag savings offered by under drive pulleys is more than offset by the reduction in horsepower due to the engine operating at a higher temperature. Under drive pulleys will deliver less horsepower at the rear wheels. Radiator Caps The radiator cap needs to be rated at the highest pressure the radiator will tolerate. All race radiators will accept a 22-24 PSI cap. Most race radiators will accept a 29-31 PSI cap. High pressure coolant has a higher boiling point and transfers heat from the cylinder heads better. The coolant only builds to 16-18 PSI from expansion from 72 degrees to 200 degrees. However, if the engine does overheat due to external factors the pressure can reach as high as 28 PSI. Once the radiator cap opens and expels coolant the vehicle will not cool back down until the engine is shut down. Consider the radiator cap a safety valve and always use the highest pressure the radiator will tolerate. Radiator Cap Location The radiator cap should be located at the highest point of the system, on the low pressure side (after the radiator core). Cross flow radiators mounted higher than the engine are ideal because the cap is on the tank that is connected to the water pump inlet. This offers 3 advantages: 1. The cap is at the highest point of the system allowing any air to migrate to the area just below the cap. If the cap opens do to excessive pressure the air will escape first. 2. This area has the lowest velocity allowing the air to seperate from the coolant even at high engine RPMs. 3. The cap is located on the low pressure (suction) side of the system so it is unaffected by the pressure generated by the water pump. If the system is anything other than a cross flow radiator mounted higher than the engine you need a surge tank for a racing application. A surge tank is basicly a 1 quart tank mounted at the highest point of the system with the radiator cap on top. The tank is connected at the bottom to the inlet side of the pump with a 1/2" to 3/4" line. A 1/4" to 3/8" bleed line connects the side of the tank to the highest point on the low pressure side of the radiator. The bleed line allows some circulation through the tank while the engine is running. The tank is large enough to allow the air to seperate as the coolant flows through it. All the air in the system will then migrate to the aera just below the radiator cap allowing the air to be force out first when system pressure exceeds the cap's rating. Street cars with an upright radiator (tanks top and bottom with the cap on the top tank) are a comprimise that will work so long as the car is not operated at sustained high RPMs.. Aftermarket thermostats housings that mount the radiator cap directly above the thermostat location are a poor design that  will push coolant out the cap at high RPMs. The aftermarket pieces that mount the radiator cap in the top hose will also push coolant out the cap at high RPMs. Thermostats/Restrictors NEVER use restrictors, they decrease flow and inhibit  cooling. Vehicles that need a thermostat to keep the engine at operating temperature should use the Howard Stewart/Robertshaw thermostat. This thermostat does not restrict flow when open. The Howard Stewart modification consists of 3 3/16" machined directly in the poppet valve to allow some coolant  to bypass the thermostat even when the thermostat is closed. This modification requires a  little longer warm up on a cold day, but allows the thermostat to operate function properly when using a high flow pump at high engine RPMs. You can never flow the water through the system so fast that is doesn't have time to cool. The system is a closed loop, so if you keep the water in the radiator longer to allow it to cool more, you are also keeping the water in the engine longer allowing it to get hotter. The water in the engine will boil away from the critical areas if not forced through at a high velocity. Older cars used low pressure radiator caps with uprught radiators. At high RPMs the water pump pressure would overcome the radiator cap and push the coolant out. the cars overheated because the coolant was pushed out. Most hot rodders erroneously thought the cars overheated because the coolant was flowing through the radiator so fast it didn't have time to cool and pushed the coolant out as a result. Slowing the water pump down and/or restricting the flow prevented the coolant from being pushed out and allowed the cars to run cooler. Cars built in the last 30 years have cross flow radiators that position the cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to the water pump pressure and benefit from increased coolant flow. Older cars with upright radiators can benefit from increased coolant flow if a higher pressure radiator cap is installed. Coolant will only be forced out during sustained high RPM operation. Coolant Water cools best. Use a corrision inhibitor comparable to Prestone Super Anti-rust with pure water. If freezing is a concern, use the minimum amount of antifreeze required for your climate. Howard Stewart has tested the "magic" additives and found none work better than water. Some of the additives will cause the water pump seals to fail. In static cooling situations such as quenching metal during heat treating, softening agents sometimes referred to as "wetting" agents will allow the water to cool the quenched part more evenly and faster. The part will  cool quicker and the cooling water will heat up faster. However, an automotive cooling system is not static. In fact, the velocities are similiar to a fire hose forcing the coolant against the walls of the water jackets. If the softening (wetting) agents actually helped in cooling the engine the temperature of the coolant as it exited the engine would be greater because it would have absorbed more heat. Fans Electric fans have improved tremenously in the past few years and now out perform mechanical fans in nearly every application except towing and dirt oval racing. Mechanical fans must have a proper shroud. Most mechanical fans have a bad vibration due to air turbulence when driven over 6,500 RPMs. This is a turbulence problem, not a balance problem. This will destroy the water pump and everything in front of it.. The large fans used my most dirt oval track racers consume up to 18 horsepower at 6,500 RPMs. Don't run a fan any larger than required to keep your engine cool. Flex fans are a bad design. They move less air at high RPMs, but consume only a fraction less power than standard fixed pitch fans. Clutch fans are inconsistant and should be avoided. Hoses Use standard full size hoses for maximim flow. Smaller AN style hoses decrease flow and inhibit proper cooling. Radiators Aliminum radiators dissipate heat better than copper-brass for  two primary reasons: 1. Copper-brass radiators must be soldered together. Solder is a very poor thermal conductor and inhibits the ability of the fins to pull heat out of the tubes. Aluminum does not dissipate heat as well as copper-brass, but does not require solder for assembly. The aluminum radiator assembly dissipates heat better. 2. Modern radiator designs incorporate wider tubes with smaller cross sections. This design allows for more contact per cubic inch of coolant. These radiators cool substantially better than the older designs that use narrow tunes with taller cross sections. The modern wide tube designs are all manufactured from aluminum. Use the largest square inch radiator that will fit in your vehicle. Thicker radiators are better than thin radiators, but thickness is no substitute for surface area. A good rule of thumb: if the surface area is doubled the potential thermal dissipation is doubled, if the thickness is doubled potential heat dissipation increases approximately 25%. The air does not get heat saturated before it gets to the backside of a thick radiator. Thicker radiators do have slightly more airflow resistance than thin radiators, but a 4" radiator has only approximately 10% more airflow resistance than a 2" radiator. Old hot rodders and racers sometimes installed thicker radiators and noticed dereased cooling. They erronously came to the conclusion that the air couldn't flow aduquately through a thick radiator and became fully saturated with heat before it exited the rear of the core. The cause of the decreased cooling was not the air flow, it was the coolant flow. The older radiators had narrow tubes with taller cross sections. Coolant must flow through a radiator tube at a velocity adequate to cause turbulence. The turbulence allows the coolant in the center of the tube to be forced against the outside of the tube to allow better heat transfer between the coolant and the tube. The coolant velocity and the subsequent ability to create the required turbulence is decreased proportionately to the increase in thickness. If the thickness of the core is doubled the coolant velocity is halved. Modern radiators with wide tubes and shorter cross sections require less velocity to achieve optimum thermal transfer. The older radiators benefited from baffling the tanks and forcing the coolant through a serpentine configuration. The velocity was thus increased and the required turbulence restored. The newer radiators seldom benefit from this multi-pass configuration because the velocity is still adequate for optimum thermal transfer in thicker radiators. Higher fin count radiators will cool better than low fin count radiators if they are clean. However, higher fin count radiators are very difficult to keep clean. The compromise depends on the conditions of operation. Double pass radiators require significantly more pressure to flow the same volume of coolant through them compared to a single pass radiator. A triple pass radiator is even more restrictive. Cross flow radiators are a much better design than upright radiators because the radiator cap is positioned on the low pressure (suction) side of the system. This prevents the pressure created by a high flow water pump from pushing coolant out through the radiator cap at high RPMs. Vehicles that must have an upright radiator should be equipped with a radiator cap with the highest pressure rating recommended by the manufacturer. The system will still push coolant out the cap at sustained high RPMs. External Plumbing Street driven vehicles seldom need auxiliary plumbing. Small Block Chevrolet race engines with aluminum cylinder heads usually need extensive external plumbing to overcome two design problems: 1. Aluminum cylinder heads have much small water jackets than cast iron heads because the external dimensions are similar, but the ports are usually larger, the deck is thicker and the material by the rocker stand is thicker, leaving less volume in the water jackets. The decreased area inhibits flow from front to rear. 2. The siamese center exhaust ports are a design comprimise that get worse when aluminum is used. The area by the center exhaust valves is thicker and thus allows for less surface area for cooling. A pair of -10 AN lines should connect the rear of the aluminum cylinder head equipped Small Block Chevrolet race engine to the thermostat housing crossover at the front. These will help offset the smaller water jackets. A pair of -10 AN lines connecting the pressure side of the pump with the area in the center of the cylinder head just below the exhaust ports will offset the lack of surface area due to the extra material. Again, only Small Block Chevrolet  race engines equipped with aluminum cylinder heads require these extra lines. Race engines without traditional intake manifolds must be plumbed to allow any air to be purged automatically. To accomplish this the coolant must be removed from the highest point of the cyllinder head. If this is impractical, -4 or -6 bleed lines must be installed at the highest points of the water jackets and plumbed to the highest point of the high pressure side of the radiator. Some cylinder heads require the bleed lines at each end. V-8 engines require a pair of -16 AN lines when the coolant is taken directly from the cylinder heads. -12 AN lines from each corner of each read routed directly to the high pressure side of the radiator is the best configuration for a V-8 engine without a traditional intake manifold. The volume with be adequate and the extra bleed lines will not be needed. Special Considerations Drag Racing A drag racing car's cooling system can't hope to cool a 1,000 plus horsepower engine under load. This task would require a radiator twice the size of a Kenworth truck's along with adequate airflow. You want to concentrate on transferring enough heat away from the exhaust side of the cylinder heads to allow a more aggressive tune-up and cooling the engine only when it is idling or shut down. Dirt Oval Gasoline powered dirt oval track cars require more water pump and fan speed than a comparable pavement car. This is due to the lower engine speeds in the corners and the possibility of clogged grill screens. A mechanical fan with a proper shroud is a must. Street Rod Nearly all street rods are equipped with an upright radiator that positions the radiator cap on the pressure side of the system. This subjects the cap to the pressure generated by the water pump. The highest pressure rating cap recommeded by the radiator manufacturer should be used, but they will still push coolant out when operated at sustained  high RPMs.