There are formulas used to determine what size turbo would be ideal for your application, but there is not enough room in this article to even begin to discuss this. Just remember that bigger is not always better, and to consult the manufacturer regarding turbo size.
Here are four air-to-air intercoolers....
Here are four air-to-air intercoolers. The compressed air enters one side, is cooled by ambient air passing over the fins, and exits the other side on its way to the engine.
- Often regarded as cooler and more desirable than single-turbo systems are twin-turbo systems. Because smaller turbos “spool” more quickly, some opt for two smaller turbochargers over one large turbocharger. There are advantages and disadvantages to this. Smaller turbos have the ability to reach maximum boost sooner, (which reduces boost lag). Lag refers to the time it takes exhaust waste to create a compressed air charge by the compressor(s). For this reason, many chose two smaller turbochargers over a single large one. Disadvantages include added cost, more weight, and more complicated plumbing (hot and cold piping).
Though the piping on a twin-turbo system may be more complex, it is better at reducing heat loss in the hot piping. Heat loss in the hot piping is energy loss, resulting in less potential of the turbocharger(s).
Intercoolers
The byproduct of compressing air is heat, and lots of it. Excess heat in the incoming air charge can lead to detonation, so intercoolers are used to remove heat from the inlet charge.
An intercooler is a heat exchanger, which cools the inlet charge. This occurs by condensing the compressed air charge from a turbocharger or supercharger system. Molecules of air are closer together when cold, allowing more room for more molecules to fit at a given time. This, combined with the right amount of fuel, will allow the engine to make more power. Also, a cooler air charge decreases the chance of knock (detonation). A hot air charge requires ignition timing to be retarded to prevent knock, thus decreasing power.
There are a number of ways to cool a compressed air charge in a forced-induction vehicle. The most popular is the air-to-air intercooler. Another growing method is the air-to-water intercooler. A less-conventional method is through water/methanol injection.
Air-to-Air - Like coolant flowing through a radiator, the compressed air flows through a block of tubes separated by fins. Cool air flows across these fins, cooling the air charge. Because of its simplicity and wide availability, the air-to-air intercooler is the most popular. Unlike air-to-water and water/methanol injection, an air-to-air intercooler’s ability to cool is constant as long as the vehicle is moving or dedicated fans are used, and most can cool an air charge by 30-40 percent.
Also, minimal maintenance, affordable price, and reliability are all major positive features of the air-to-air intercooler. These factors make the air-to-air intercooler the choice for most street applications.
Air-to-Water - Air-to-water intercoolers use ice water or ethylene glycol, stored in a reservoir and pumped through the system to cool the inlet charge. In this case, the intercooler acts more like the evaporator core of an A/C system, where the air charge actually flows over the coils of the intercooler instead of through it. The water collects heat from the air charge and is then pumped through the tubes of a heat exchanger (mounted in front of the radiator), where air then flows through fins to cool the water.
This method is extremely effective (more than an air-to-air) for a short period of time. Then, the water/coolant begins to become heat soaked. To maintain maximum cooling capabilities, the ice must be replenished, or the coolant must be allowed to cool.
Air-to-water intercoolers are most popular on Roots-type and twin-screw superchargers and are usually mounted in the valley of the engine below the supercharger. Air is forced directly through the intercooler as it exits the outlet port of the supercharger.
Water/Methanol Injection - Lately, some companies have developed systems that inject a mixture of water and methanol fuel into the intake tract of a forced induction engine. “Think of it as chemical intercooling,” says Matt Snow of Snow Performance. “It’s ideal for cars with no room for intercoolers.” On a street application making 15 psi of boost, water/meth injection can reduce air temps from 180 to 190 degrees to 120 to 130 degrees—a 60-degree drop.
Not only does it cool and condense inlet air, but it also raises the effective octane of the fuel. “With 91 octane pump gas and a 50/50 water/meth mixture, we can meet or beat 116 octane race fuel,” says Snow. The mixture slows combustion, making combustion more controlled, and allowing a leaner air/fuel mixture and more-aggressive ignition timing.
The disadvantage to water/methanol injection is that is it is consumable. Once your two-and-a-half-gallon container is empty, you must refill it to regain benefit.
This is an example of an air-to-water...
This is an example of an air-to-water intercooler. The air flows into one large opening and is cooled by either ice water or ethylene glycol as it passes over the fins and exits through the outlet.
Here is a typical air-to-water...
Here is a typical air-to-water intercooler integrated into an intake manifold for a positive-displacement supercharger. The supercharger is removed for this photo, but normally sits atop the manifold directly over the intercooler.
This is a water/methanol injection...
This is a water/methanol injection kit from Snow Performance. It includes a tank, pump, plumbing, and wiring. After installation, tuning is required to maximize the effects.
Wrap It Up
As many Ford owners know, there’s no better way to bolt-on horsepower like a forced induction system. You can start with a completely stock car, install a blower or turbo system (often in a day or two), and nearly double the power output, or more!
With the amount of support provided by aftermarket manufacturers, Mustang and Ford owners are living the good life when it comes to forced induction system options, price, and reliability. There are already nearly a dozen kits available for the ’11 5.0L Mustang GT, with many more to come. There’s no end in sight, and it will be exciting to see how these systems improve even more over the coming years.
(Author’s Note—When writing this story, the following publications provided invaluable information: Maximum Boost and Supercharged!, both by Corky Bell.)