Sep. - Oct. 1998 Lane Racing And Rodding Article By Jim Kaekel, Jr.
Although most of the dog days of summer have passed us by, there is still the possibility that we'll have to endure some more 90 degree weather while we participate in our favorite automotive-related diversions. There's no doubt that high summer temperatures are hard on the parts of the human body that power us, but they're even tougher on the drivetrains that power our race cars, street machines and street rods. Let's take a technical look at keeping that high performance machine cool. After all, what could be more miserable than sitting in 90 degree heat and having to tend to an overheated engine because we neglected our cooling system?
Keep in mind that modified engines and drivetrains will generally run hotter than those that are unmodified and, for that reason alone, the cooling system is a very important part of any high performance automobile. Higher compression ratios, for example, create higher cylinder temperatures and, consequently, more work for the cooling system. Installing a deeper (lower) rear end ratio to improve performance will also contribute to higher coolant temperatures because the engine will run at higher RPM at a given speed. Automatic transmission cars equipped with high stall speed, performance torque converters tend to build more heat due to the increased slippage. Most hot rods and race cars have at least two of the above modifications, so an efficient cooling system is very important.
Many remedies are available for overheating, but rather than pursuing miracle cures for an inadequate cooling system, let's cover the basics of sound cooling system design. Keep in mind that with cooling systems, an ounce of prevention can be worth a truckload of cure. Many factors must be taken into consideration when evaluating the efficiency of a cooling system. Radiator size and condition, condition of belts and hoses, coolant mixture, water pump design, water pump/crankshaft pulley ratio, type of fan and shroud, and thermostat type and opening temperature are all heavily involved.
The radiator should have sufficient size and capacity for the vehicle/engine combination. If a 454 engine with air conditioning is being swapped into a Chevelle formerly powered by a non-A/C 350 engine, it's a safe bet that the original small block radiator, even if it's like new, is not going to be up the task of cooling an extra hundred cubic inches. Most six cylinder and small block V8 cars use a two-core radiator, but when a swap or major hop up is planned, the original radiator should be replaced with at least a three-core or four-core unit. To determine size of the current radiator, simply remove the radiator cap, look inside the top tank and count the number of rows of tubes. If there are three or four, and the radiator is in good shape, it might just be worth a try. If there are only two rows, get that radiator out of there now and replace it with a bigger one. Want ultimate cooling? Use an aluminum radiator. Aluminum dissipates heat much more quickly than original equipment copper/brass designs, and Griffin, Howe, and Be Cool all manufacture aluminum, OEM-style replacement radiators with the hot rodder in mind. Regardless of which larger radiator is chosen, fill it with a proper 50/50 mixture of water and high quality anti-freeze.
Next, be sure belts are in good shape, adjusted properly and not slipping. Another important consideration with belts involves sizing. There are several different belt widths and cross section angles, making it necessary to carefully match belts to pulleys being used. If care is not taken here, belts may slip or get thrown off completely at high rpm because they are not making proper contact with the sides of the pulley groove.
Hoses are equally important. It's likely that blown or leaking hoses comprise the largest single cause of cooling related roadside breakdowns. Hoses that are hard and cracked, or soft and bulging hold the potential for major problems. Also, always be sure that the special spring inside the bottom radiator hose is intact. This spring prevents hose collapse.
Conventional, belt-driven water pumps are available in several configurations ranging from completely stock to aftermarket, high flow aluminum pumps. Generally, OEM water pumps for air conditioning applications will be fitted with higher flow impellers than non-air units and may just provide enough extra flow to combat minor overheating problems without spending a young fortune. If the overheating problem is more severe, high flow aluminum pumps from Edelbrock, Weiand, or Stewart can be called upon to battle the heat. Aside from high performance impellers and bearings, these aftermarket water pumps are also designed to equalize flow to both sides of the engine for more uniform cooling.
While we're on the subject of belt-driven water pumps, water pump-to-crankshaft pulley ratios also play an important role in keeping a hot rod cool. A smaller diameter water pump pulley will increase water pump speed and flow and this often will cure a vehicle that overheats, particularly at low cruising speeds. Small water pump pulleys can be commonly found on vehicles originally equipped with air conditioning, or from companies like Moroso, Canton, and March.
In serious street/strip machines, a belt driven pump may or may not provide adequate cooling, but one thing is for sure: it will rob horsepower from the engine it sits on. Moroso, CSI, and Meziere offer electrically driven water pumps which not only guarantee high flow, but run at maximum speed regardless of engine speed, and do not rob horsepower. CSI and Meziere offer electric pumps for almost all popular engines.
Right up there, in terms of importance, is the fan. Belt-driven fans are generally mounted right on the water pump pulley and turn at the same rpm as the pump. Available in two different styles, standard and clutch type, fans are rated on their diameter, blade count and pitch. For instance, an 18", 6-blade fan will pull more air through the radiator naturally than a 15", 4-blade model. Clutch fans contain a clutch unit to reduce fan speed during high speed driving for increased performance and mileage. Fans should always be used in conjunction with some type of shroud which aids the fan in drawing air through the radiator. Without a shroud, a fan just pulls through an area of the radiator equal to the area of the fan, but with a shroud, the fan can pull air through the entire surface of the radiator. Shrouds are often discarded during an engine swap and then later re-installed when an overheating problem occurs.
Replacing the belt-driven fan with an electric fan, such as those manufactured by Flex-A-Lite, Derale, Mr. Gasket, and B&M, will increase efficiency and gain several horsepower to boot. Electric fans are great for applications where space is limited, like under the hoods of most street rods. When selecting an electric model, be sure it is of sufficient diameter and airflow (measured in CFM or cubic feet per minute) for the application. Electric fans can be mounted behind or in front of the radiator and wired to run constantly, or on demand.
Thermostatic switches are also available which can be adjusted to activate at a pre-determined temperature.
The final component we will consider in the cooling system is the thermostat. Selection is limited to designated temperature opening, and design and size of the opening which regulates coolant flow. Most hot rodders prefer a 160 or 180 degree thermostat for cooler operating temperatures. The high flow, balanced thermostats, available from Mr. Gasket, can aid in increasing coolant flow over conventional type thermostats. Rodders using a 160 degree thermostat may find it necessary to switch to a higher temperature unit if their vehicle is to be driven year round to insure good heater and defroster operation in colder temperatures.
Hopefully, this cool advice will serve its purpose and keep an overheated engine from spoiling an otherwise fun rod run or cruise.