Building blocks of interc...
Building blocks of intercooling.
If you think about it, trickery plays a big role in performance tuning. We fool the ECU into giving us more power with black boxes. We trick the fuel system into delivering more fuel by upping the pressure, and in the biggest con of all, we fool the atmosphere by compressing it and doubling and tripling its volume inside our engines. While forced induction is the big trick, intercooling also serves to befuddle the atmosphere in the name of power.
Intercooler Mission Statement
An intercooler's trickery centers on air density. During compression, charge air is heated and with this heat comes a decrease in air density. Density can be viewed as the amount of molecules in a given volume of air. Intercooling reverses the heating trend and endeavors to recapture some of that density.
The amount of density regained depends on the ambient temperature of the air (in air-to-air units), the efficiency of the compressor (max boost, wheel efficiency etc.) and the cooling capacity of the intercooler.
A properly sized turbo that operates at or near its peak efficiency will not heat the charge as much as a mismatched unit that has to overspeed to generate the desired boost. This extra effort results in a chopping of the air, which nets high outlet temperatures.Because of its charge chilling capabilities, the intercooler also ups the detonation threshold and, as a general rule, a good intercooler will allow you to run three to four more psi without experiencing any detonation.
The charge side is where boost...
The charge side is where boost travels to be cooled on the way to the engine. Here we see a fin comparo with the popular low-pressure drop, high-speed plain square fin (right) and an offset fin design (left). The offset fin will allow the air to travel slower through the core (more pressure drop) but the air will have more time in the core for heat exchange.
Intercoolers are constructed in a number of different ways. The most popular are bar and plate and tube and fin. We cornered Johnny Wang, Spearco's product manager of heat exchangers, in the intercooler inventory room and would not let him leave until he answered some questions.
Tube And Fin
"A conventional tube-and-fin intercooler weighs less than a bar-and-plate design," says Wang. "Typical tube-and-fin units utilize extruded tubes with fins pressed into place. In order to achieve strength, a thick, extruded tube must be used.
"The tube-and-fin core is held together and its seal is created at the joints at the end of the plates, which is usually .125 inches thick. The width of the tubes is less than the width of the side plate. Space is lost where the joints for sealing are used. So a 3.5-inch core will have tubes only 2.87 inches wide."
Unable to maneuver around the machinery, Wang continued, "Also, fin design in the charge side, inside the extruded tubes, was limited by the extrusion machine, which impeded the design of charge side fin geometry to meet individual custom applications. While this design did allow varying ambient fin designs, the charge air shortcomings proved too much of a handicap.
"Tube and fin has a larger leakage rate compared to bar-and-plate cores. Furthermore, tube-and-fin cores are more susceptible to road damage from rocks and debris than bar-and-plate cores; big trouble in front-mount applications. The oval tubes are extruded from thin-wall material and any sort of extreme pressure can cause these tubes to 'balloon.' In today's high-performance industry, high boost levels are the key power."
On the ambient side, where...
On the ambient side, where oncoming air streams through the unit, fin design is equally important. Fin density here also impacts cooling performance but there is often the vehicle's cooling system to consider.
Bar And Plate
Wang had a more upbeat tone when it came to bar-and-plate construction. "Spearco pioneered bar-and-plate core design. True, the bar-and-plate design is a bit heavier than tube and fin, but this is actually advantageous.
"The core acts as a heat sink. Its ability to soak up more heat is especially useful in stop-and-go traffic. It keeps the charge relatively cool, then is able to dissipate the heat once the vehicle is in motion. Tube-and-fin units can't pull this off.
"A bar-and-plate core can take the damage of front-mount life and endure high boost without flinching. Sealing is superior in bar-and-plate units because the bars and brazing sheets run the length of the unit, providing a 100-percent seal between the ambient and charge sides.