Muscle Mustangs & Fast FordsHow To Engine
All About Intercoolers
Boosting Your Engine Is Fun-You Can Do Better With An Intercooler
There's no denying that supercharging and turbocharging engines is becoming more and more popular every day. Substantial increases in horsepower and torque, along with stock-like driveability make these power adders very appealing to a great many enthusiasts. In order to take these power gains to the next level, an intercooler must be employed, and we're going to tell you why you might need one, and what is available for your muscle Mustang or fast Ford.
The term intercooler actually dates back to the beginning of air-charge-cooling technology when piston-driven aircraft used multiple superchargers to boost power output. Air-charge coolers were installed between these superchargers (hence the inter part of the name) to reduce the air-charge temperature. Technically speaking, most of the current air-charge-cooling designs should be called aftercoolers since they chill the charge after the compressor, but the market has been slow to adopt the more accurate description. At this point, the term intercooler is used much like Kleenex or Coke, in that they have come to represent the type of product rather than a brand or exact product. For the duration of this article, we'll refer to intercoolers and aftercoolers simply as charge coolers.
In order to understand air charge cooling, or the concept of cooling the air that enters the engine, you must first realize that superchargers and turbochargers both pressurize the intake side of the engine. When you add more air and fuel, the result is usually increased power and torque. Compressing air, however, has the drawback of heating the air charge going into the engine. Heated enough, the hot air can cause detonation, among other serious issues.
To combat the increase in air temperature, a charge cooler (intercooler/aftercooler) is employed. By forcing the compressed, and subsequently heated, air intake charge through an intercooler, the emperature is reduced, as is the air pressure from the restriction posed by the intercooler. When both of these events occur, the result is a cooler and more dense air charge. The dense air charge, when combined with the appropriate amount of extra fuel, produces more horsepower and torque. The cool, dense charge also allows for more ignition timing to be run, which also adds to the increased power output.
Now that we've established the reasoning behind using a charger cooler, it's time to talk about cooling methods. Currently, there are two particular types of charge cooling methods that are used in the automotive industry. The first, and most common, is the air-to-air charge cooler. In this setup, air is passed through a cooler core, which is usually placed at the front of the car in the direct path of oncoming air. The air passes over the fins of the core, which pulls the heat from the air charge within the core. Some manufacturers use a top-mounted cooler, such as with the Mustang SVO, but for vehicles with larger engines, there usually isn't enough space to fit them above the engine.
The air-to-liquid charge cooler transfers the intake charge heat to an intermediate fluid, usually water or a common automotive coolant, which is passed through its own heat exchanger that is air cooled. Such systems have been used in all of Ford's most recent supercharged applications, starting in 1999 with the SVT Lightning and continuing with the SVT Terminator Cobra and Shelby GT500.
"The air-to-water setup is very efficient," says Ford Racing Performance Part's Jesse Kershaw. "It's more complex and difficult to add after the fact, but when we started from scratch, it made it easy-especially with a V-engine-because the core fits in the valley."
Air-to-water charge coolers are usually heavier than air-to-air systems because of the additional components that make up the system-fluid, circulation pump, radiator, and plumbing. Though they may be heavier in weight, air-to-liquid charge coolers generally feature lower overall pipe and intercooler length, which can reduce turbo lag.
"Running coolant hoses is far easier than large-diameter air tubes, and in the case of a crash, there is less radiator up front so it's better protected. It won't incapacitate the engine if it's ruptured (if damaged, air-to-air wouldn't run), and it doesn't block the A/C condenser and radiator as much as an air-to-air," notes Kershaw.
The air-to-liquid setup seems to lend itself better to racing applications, because the fluid reservoirs can often be filled with an ice water mixture that can drop intake temperatures well below the ambient air temperature. The air-to-air crowd does something similar in that they spray nitrous oxide or carbon dioxide on the front-mounted charge cooler core to further reduce intake-charge temperatures. The reduction in intake-charge air temperatures is quite substantial with either design.
"On the Lightnings, we saw an approximate 100-150 degree drop in inlet temperature depending on vehicle speed versus engine load," says Kershaw.
In addition to supplying the engine with more air that it wouldn't have otherwise, the resultant internal engine temperatures drop as well, which allows for a more advanced and more powerful ignition-timing map.
As previously mentioned, the late-model SVT and Shelby products all use air-to-liquid charge coolers from the factory, and the aftermarket has produced a plethora of parts to make these systems more efficient. You can extract more power from the factory systems with these components, but more importantly, they provide proper cooling increases that support higher power levels. Companies like Fluidyne, Afco, Canton, Steeda, Precision Fabrication, and others all make high-performance heat exchangers and/or reservoirs that provide superior cooling and capacity, and most parts are drop-in replacements for the stock pieces.
Back in the mid-'80s, it was the technologically advanced Mustang SVO that led the way in forced-induction for the Mustang market. By the late '80s, the centrifugal supercharger aftermarket came alive, and it wasn't long before the benefits of charge cooling were integrated into the supercharger systems. Accessible Technologies, better known as ATI ProCharger, came to market with an intercooled supercharger kit for the Fox-body Mustang in 1994. It featured a two-core air-to-air intercooler, and offered a three-core unit as an upgrade.
"With intercooling, we could reduce the charge air temperatures dramatically, increase air density, and safely run more boost," says ATI's Ken Jones. "Charge air temperatures are reduced by approximately 90 degrees at 9 psi-about 25 degrees above ambient air temperature." ATI has kept with the air-to-air charge air cooler and uses them in the company's latest products. "Air-to-liquid coolers not only offer less heat reduction/temperature drop to begin with, but they typically heat up after repeated pulls and power fades badly," says Jones.
Vortech Engineering came out with its own air charge cooler, the Power Cooler, a few years after ATI's debut, and the company opted to go with the air-to-liquid route with its charge cooler. "The air-to-liquid design has several benefits," says Vortech's Mike Reagan. "It's easier to package and offers less frictional losses because there are less bends and shorter lengths to the tubing. An air-to-air charge cooler requires extra horsepower to push the air through the tubing." Reagan also claims that air-to-air coolers cause higher intake air temperatures because of the friction that results from the design, and he also tells us that depending on the way a car is driven and the ambient air temperature, they have seen decreases in air charge temperature of over 100 degrees.
Beyond centrifugal superchargers, the Roots- and twin-screw-style superchargers from Kenne Bell, Magnuson, Roush, Saleen, Ford Racing Performance Parts, and Whipple all use air-to-liquid charger coolers. When it comes to Mustang turbocharger systems, the verdict is overwhelmingly air-to-air charge coolers. Hellion, HP Performance, B&G Custom, Granatelli Motorsports, and all others utilize the air-to-air setup.
"The air-to-air cooler has less maintenance, it's easier to install, and has a lower cost-the air-to-water coolers require a reservoir, a pump, two heat exchangers, and other components," says Hellion Power System's John Urist. He does, however, present an open-minded approach to charge cooler selection.
"You don't want to tell people one thing, because there are so many variables within each combination. Every one is different and has difference requirements that must be met. With the air-to-air, you generally want to fit the biggest one you can in the car. You're usually limited by the space available."
With regard to the air-to-air charge cooler, there are two different designs, and Urist, along with ProCharger, prefer the bar-and-plate cooler over the less expensive and less efficient tube-and-fin design. Most of the charge coolers you find for cheap on eBay are of the tube-and-fin design, so buyers beware.
That about covers the street applications in the Mustang aftermarket. Beyond the street, there are companies like Precision Turbo, JPC Racing, and Dez Racing that are building bigger, better charge coolers and installing them into cars making anywhere from 500 to 2,500 hp.
Always the pioneer when it comes to the S197 Mustang, JPC Racing in Glen Burnie, Maryland, offers air-to-liquid charge coolers for the S197 Mustang that use any of the available aftermarket centrifugal superchargers, including Paxton, ProCharger, and Vortech. JPC has also been known to fabricate the necessary tubing to connect them to some of the popular S197 Mustang turbocharger kits.
Precision Turbo, in addition to selling turbocharger units for everything and anything, also sells its own line of charge coolers. Precision offers everything from Ford Focus 2.0L charge coolers up to tube-chassis, 200-mph race cars.
"Over the last couple of years, there have been significant advancements in the air-to-water intercooler technology, specifically in regard to the cores," says Joe Krivickas, sales manager for Precision Turbo. "This allows us to build a smaller, lighter, more efficient unit that will support more power, yet weigh less than similar units from years past. More importantly, we have been working on the safety aspects of the construction. We continue to review the welding process and tank materials to keep up with the higher boost pressures as turbo sizes grow."
The battle over which charge cooling method is better has been going on for decades now, and we see no end in sight. In a drag-racing application, the winner has to be the air-to-liquid charge cooler. Being able to chill the intake charge with ice water is just unbeatable, especially in classes where only a single power adder is allowed. When it comes to everything else, it's basically up to the manufacturer of the supercharger or turbocharger, as well as your opinion on the design of the charge cooler and how it integrates into the vehicle.
Both methods have their benefits and drawbacks, but one thing that can be said for both is that they help increase horsepower and torque, and you can't go wrong with that.