7. Do you recommend mechanical or electric fans?
Be Cool
Electric fans are preferred because sufficient airflow is maintained at idling or low ground speeds. Airflow supplied by a mechanical fan changes with engine rpm and can be insufficient at low-engine rpm, and also uses up horsepower.
Flex-a-lite
With most cars and light trucks, the installation of an electric fan is a great choice to free up horsepower and increase fuel mileage. If the vehicle is to be used under "extreme" conditions, such as towing or when using a four-core radiator, the use of the original belt-driven fan may be a better option.
Griffin
If the car still has a properly operating mechanical clutch fan, it will pull more cfm than an electric fan, and consideration should be given to keeping it. If the mechanical fan clutch is not working properly, then it should be replaced or an electric fan can be used. Keep in mind that the only time a fan should be necessary is when the car is standing still. If an electric fan will keep the car cool while at idle, then an electric fan is fine. Today's electric fans are producing more cfm than ever, and 3,000 cfm is common.
Mattson's
The engine-driven fan is great for higher speeds. We recommend one if you have a vehicle that does a lot of towing and driving at highway speed. It's a good idea to use the engine fan. If a vehicle does a lot of idling, cruising, or driving slow, the electric fan on a shroud is the way to go.
U.S. Radiator
Why rely on another operating system (that being electrical) if you don't have to? Mechanical fans turn when the motor turns. However, we highly recommend a shroud properly fitted to the fan and radiator. The only time you really depend on a fan is at idle or low speed where there is little or no air flowing through the grille. Shrouds are necessary to maximize the amount of ambient air being pulled through the grille and radiator. Proper fan and shroud alignment should have the leading edge of the fan 1/3 in, and trailing edge 2/3 out. The airflow off the back of the fan deflects at about a 45-degree angle when set this way. When the blade extends farther into the shroud, the air off the back of the blade flows straight back into the block and decreases the airflow efficiency by about 15 percent.
If an electrical fan is the only way to go, place it on a shroud that covers the entire core. We often see an electric fan attached directly to the core and the only thing this does is waste the rest of the core surface when you need it the most. A 16-inch electric fan attached to a core only cools a 16-inch circular section of that core.
Walker
Mechanical fans with fan shrouds work well. The main problem with a mechanical fan is that you should never use less than 17 inches in diameter and never without a fan shroud. We have found the engine will take longer to recover with a mechanical fan rather than with an electric fan when you have to make a sudden slow-down or stop in extreme temperatures at interstate speeds.
Electric fans work well if they are properly sized. As a rule, you should never use less than a 16-inch-diameter blade. Hook design blades are more efficient and are quieter than a paint stir stick design.
8. How much pressure should the system be under?
Be Cool
It depends on the application. Under normal street conditions, the cooling-system operating pressure will be under the rating of the radiator cap. All Be Cool radiators are designed to function with a 13-psi radiator cap. If the cap allows the radiator to vent frequently, there is another problem with the cooling system. The radiator may be too small, the electric fan may not have the correct flow rate, or the water pump may be incorrectly sized.
Flex-a-lite
In older vehicles without a coolant-recovery system, the pressure can be as low as 7 lbs. The system on these older cars would expand, forcing the coolant out and then leave a cavity in the top tank after they cooled. In vehicles with a coolant-recovery system, the pressure can be about 16 lbs.
Griffin
Up to a 17lb cap can be used for street use. Circle-track racers run between 22-29 lbs. For higher pressures, such as Nextel Cup or Busch Series cars, Griffin manufactures the Survivor Series, which will handle 50-60 lbs.
Mattson's
It's always best to use the factory recommendation; however, there are sometimes no recommendations available to the customer for the modifications to old cars with late-model engines. The radiator cap has a spring that will lift up and allow the fluid to escape through to the overflow. The different-pound caps will lift up at different temperatures. A 13lb cap is most common, with a 16lb cap raising the boiling point even higher. A 7lb cap is common in the older vehicles. If a higher-pressure cap is used on the wrong system, it may make the radiator tank come apart.
U.S. Radiator
By increasing the pressure by 1 lb, we increase the boiling point by 3 degrees; so, by running a 12lb cap, our water won't boil until it gets to 248 degrees. An engine that wants to run at 248 degrees will open that cap up long before it gets that hot.
Walker
Pressure systems have been around for quite sometime. Older systems started at a 4lb rating; 7lb systems were introduced in the '50s, followed by 15-17lb systems in the '60s, and today's engines run up to as much as 20 lbs. As a general rule of thumb in the street-rodding world, a 15-17lb system works well.
9. How is proper radiator size determined?
Be Cool
One would need to know the required number of Btu/min that needs to be rejected by the radiator. With a given air and coolant speed, select a core that will reject the required amount of heat with a factor of safety. Experience also plays a large role.
Flex-a-lite
Radiator size is determined by the requirements of the available mounting area, the powertrain, and how and where the application will be used. The correct radiator can be determined once these factors are reviewed.
Griffin
There are many factors to consider when sizing a radiator. Not all radiator sizing is based strictly upon the horsepower that the engine is producing, but also the type of fuel the car is running, how much grille area we have to work with, and under what type of driving conditions the car will be used. For most street applications, a good rule of thumb is 1 square inch of core surface per horsepower for a two-row 1-inch tube aluminum radiator.
Mattson's
We try and put the largest radiator in the available area.
U.S. Radiator
There are formulas to determine appropriate radiator size based on engine heat output (operating Btus) and radiator heat transfer rates (also stated in Btus), but my recommendation to a hobbyist is to put in the most efficient radiator that fits up to a four-row copper/brass or two-row aluminum core.
Walker
Unfortunately, being a performance radiator designer and manufacture, we have to use the area given to us (the square inches of the frontal radiator area) by the original automobile manufacture or the custom-car builders. From there, we will need the engine specifications, its modifications, and also its determined air-management package to be used. It is good to remember that the air-management package is just as important as the coolant-management package in their designs and ability to work together.
10. Do you recommend recovery tanks?
Be Cool
Yes, all the coolant that is vented from the radiator by the overflow should be reclaimed by a recovery tank. Recovery tanks allow the cooling system to replenish and helps to ensure that the radiator is always full.
Flex-a-lite
The requirement of a coolant-recovery system is not only environmentally sound, but a good idea to maintain a constant level in the cooling system. Most coolant is not environmentally friendly. It is a pollutant, and therefore should not be released to the ground. Maintaining a constant level in the cooling system will allow it to function better and prevent air from entering the system that could bring with it contaminates that might cause a failure in the cooling system in the future.
Griffin
Absolutely.
Mattson's
We recommend a recovery system on everything we do today.
U.S. Radiator
Rule of thumb is to buy the largest one that will fit in the engine compartment and still look cool. Check the recovery tank often and you'll know the size is inadequate if you find it empty.
Walker
It's a must in the performance field, and it's an advantage but not a cure-all in the street rod world. If you have the correct cooling system design, don't waste your money (I have never needed one).