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  • Intercooler Information

    This is just an FYI post because I've seen a lot of misinformation in the threads going back and forth on this topic.

    Neither air-to-air or air-to-water is inherently superior to the other. They both have advantages and disadvantages that make one more suitable than the other depending on the application.

    Adiabatic efficiency
    In normal trim, air-to-air has a higher adiabatic efficiency than air-to-water. At the track, however, you can add ice to your water to make air-to-water match the efficiency of air-to-air. But adding ice does NOT make it more efficient!

    Air-to-air advantages
    Much lower cost
    Higher adiabatic efficiency on the street
    Maintenance-free: no moving parts

    Air-to-water advantages
    Much smaller size--makes ducting that much easier

    Generally, air-to-air are superior for street cars in many applications because of the benefits listed above. Air-to-water, however, are smaller and allow for a direct path between the supercharger and the throttle body. With an air-to-air setup, air must first go through the supercharger and then through a long series of pipes in order to reach the intercooler (which is often mounted below the radiator or elsewhere close to the ground), then back up into the engine again. For an application with limited space, air-to-water is the way to go. But for most street vehicles (including V6 F-Bodies that have plenty of room under the hood), air-to-air is a popular choice.

    For further information, the following is taken directly from www.procharger.com.

    Air vs Water
    Accessible Technologies manufactures both air-to-air and air-to-water intercooler systems, and the guidelines for their usage are fairly straightforward.

    For automotive street applications, air-to-air technology is easy to install, highly effective, extremely reliable since it has no moving parts, and requires no maintenance. Air-to-water intercooler systems, on the other hand, are much more difficult to install as they contain an intercooler, a separate radiator to cool the water, a water tank, and a pump. But probably the biggest drawback to air-to-water on the street is that this technology requires the addition of ice to match the efficiency of air-to-air technology. Additionally, the requirement of ice and the possibility of pump failure or leakage means that air-to-water is also inherently less reliable.

    For race-only applications, air-to-water works well since the need to add ice at the track prior to each run is not a big drawback. The other issues are the same as listed above for street applications, and efficiency will be comparable with the use of ice.
    Regarding intercooling in general, here is some other information, also courtesy of Accessible Technologies, Inc.

    The Fundamental Solution
    All non-intercooled superchargers operate with an intake manifold temperature in the general range of 115° - 200° above ambient (outside air) temperature at 8 psi. At the same boost level, an intercooled supercharger operates at only 28° above ambient! This tremendous advantage from cooler air is just like the difference between driving your car on a cold winter's day vs the blistering heat of summer! Thats a real advantage that yields real performance. It helps to understand that no supercharger alone will ever begin to match the system efficiency of an intercooled supercharger system. This is simply because compressing air creates heat, as dictated by the laws of physics (Boyle's Gas Law). Even in the case of "perfect compression" (100% adiabatic efficiency, which is physically impossible without an intercooler), air temperature would increase by approximately 71° at only 8 psi, while the lower (40-80%) efficiencies of all non-intercooled superchargers produce substantially higher temperatures. Intercooled systems are the fundamental, OEM solution - because not only is less heat created when the air is compressed, the majority of this heat is actually removed through intercooling.

    The bottom line is that intercooled boost is substantially more powerful and safe for your engine than hot, non-intercooled boost. Now that technology has developed to the point that gear-driven superchargers are powerful enough to reliably blow through an intercooler, it simply doesn't make sense not to intercool, especially for fuel injected applications running pump gas. In fact, for high compression engines or continuous duty applications, such as marine or towing, intercooling is absolutely essential for reliability.

    In basic terms, compressing air creates heat, while intercooling removes heat.

    Benefits of Intercooling

    </font>
    • Greatly Reduced Intake Temperature
      An 85° - 200° drop in air temperature (dependent upon application) results in a more dense, powerful fuel/air charge, greatly reduces exposure to detonation, and virtually eliminates the "power fade" felt in back-to-back runs and extended pulls without intercooling</font>
    • Full Timing
      This reduction in temperature allows you to run factory (or close to factory) timing, and avoids the substantial horsepower loss inflicted by excessively retarded ignition timing</font>
    • More Low-End Boost and Horsepower
      The intercooler also acts as a passive wastegate, flattening the boost curve at higher rpm's and allowing more boost to be dialed in at lower rpm's</font>
    • An Expanded Power Band
      Full timing and forced induction keep the engine pulling hard to the redline</font>
    • More Boost
      Not only will you experience the above benefits at any boost level, you can also safely run substantially more boost when intercooled!</font>
    Reliable High Performance
    Clearly, the only type of performance that matters is reliable performance, and detonation is the single biggest threat to engine reliability. The boost range for reliable performance, without detonation, can be determined by looking at the type of supercharger technology being considered, and the compression ratio of the motor. With a lower compression ratio, an engine can safely handle more boost, everything else being equal. Similarly, if the temperature of the compressed air is lower, an engine will have a much higher detonation threshold (the point at which fuel ignites without a spark), and will be able to safely handle more boost. The overall efficiency of the entire supercharger system can be increased by both leading edge supercharger efficiency and the use of intercooling. The amount of heat produced (adiabatic effiency) by each supercharging technology is what determines the boost limitation. While gear-driven centrifugal is clearly the superior supercharger technology, it is also clear that the biggest benefit comes from intercooling. These calculations assume moderate timing, 92 octane pump gas, and a good supply of fuel to the cylinders. As mentioned previously, detonation is the single biggest threat to engine reliability. It is heat and detonation that cause blown head gaskets and burned pistons, not boost. Achieving maximum performance from a given engine while avoiding detonation requires the right combination of intake air temperature, timing and fuel quality. For example, without intercooling a stock 5.0 with 9.5:1 compression ratio can only hold 5-6 psi of boost before detonation becomes a problem. The only way to safely run more than 6 psi of boost and still make a meaningful increase in power without an intercooler is by using racing fuel to avoid detonation. Many companies also employ "band-aids" such as ignition retard and larger injectors to run 8-9 psi on pump gas, but the resulting increase in performance is only marginal (since both of these band-aids suboptimize) and detonation is frequently still a problem.

    Detonation
    We've all heard of this, but what is it? Detonation, or engine knock, occurs simply when fuel pre-ignites before the piston reaches scheduled spark ignition. This means that a powerful explosion is trying to expand a cylinder chamber that is shrinking in size, attempting to reverse the direction of the piston and the engine. When detonation occurs, the internal pneumatic forces can actually exceed 10x the normal forces acting upon a properly operating high performance engine. Detonation is generally caused by excessive heat, excessive cylinder pressure, improper ignition timing, inadequate fuel octane or a combination of these. Of the previous, excessive heat is usually the culprit. As an engine is modified to generate more power, additional heat is produced. Today's pump gas will only tolerate a finite amount of heat before it pre-ignites and causes detonation. Although forced induction engines usually produce far less heat than comparable naturally aspirated high compression engines, the cylinder temperatures in intercooled engines are radically cooler yet. It is rarely boost that causes detonation, just unnecessary heat. An intercooler is such a natural solution for forced induction, that in almost every OEM application, intercooling is part of the package.

    [ February 22, 2004, 05:36 PM: Message edited by: Stefan ]

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