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What is Intercooling?

Intercooling is the process of cooling the heated (and pressurized) intake air after the turbocharger or supercharger before it enters the combustion chamber.

There are 2 main types and 3 basic styles of intercoolers.

Air to Air Intercooling

Air to Air Intercooler
Air to Air Intercooler - Image courtesy of AMS Performance
Air to Air Intercoolers are the simplest, cheapest and most used intercoolers. They use the air that is flowing through the intercooler to cool the charged air inside the intercooler. They are basically a radiator that cools the air instead of coolant inside the engine.

Air to Liquid Intercooling

Air to Liquid Intercooler
Air to Liquid Intercooler mounted to a supercharger - Image courtesy of ih8mud.com forum
Air to Liquid Intercoolers are much more complex and therefore more expensive. They use a separate cooling system that covers the intercooler to cool the air inside the intercooler. But they also allow for better placement and short routing (tubing) and therefore offer less Turbo Lag. These systems are very common in marine applications due to the unlimited access to cool water.

Front mounted intercoolers

Front Mount Intercooler
Front Mounted Intercooler - Image courtesy of AMS Performance
Front mounted intercoolers are placed in the front of the vehicle. This area of the vehicle allows for larger intercoolers to be installed and therefore cools the charged air more. But the down side of front mounted intercoolers is the amount of tubing required to plumb the intercooler. The charged air must go from the engine (turbo or super charger) to the front of the car and then back to the engine (or intake). The problem with large amounts of tubing is "Turbo Lag", it takes longer for the turbo or super charger to build pressure.

These intercoolers often require an open bumper design and are exposed to debris. Therefore they are susceptible to clogging or damage that can hurt performance in racing conditions.

Side mounted intercoolers

Side Mount Intercooler
Side Mounted Intercooler - Image courtesy of Kereta.info
Side mounted intercoolers are placed on the sides of the bumper or in front of the wheels. These intercooler are usually used when there are space restraints that do not allow front mounted intercoolers. They still have the same "Turbo Lag" issues as the front mounted intercoolers but not the exposure issues. Many times two smaller intercoolers are used to try and match the benefit of one large intercooler.

Top mounted intercoolers

Top Mount Intercooler
Top Mounted Intercooler - Image courtesy of Roo's Rule
Top mounted intercoolers are located on top of the engine and use a hood scoop to direct air over the intercooler. This design allows for shorter routing and less tubing and therefore the Turbo Lag is much less than the other two designs. The down side of this design is that to heat from the engine can lessen the affects of the intercooler, meaning performance can be compromised.

Why do we need intercooling?

Compressing the air via a Turbo or Supercharger creates pressure and high heat. The pressure creates more horsepower but the high heat reduces the density of the charged air. The less dense the air fuel that enters combustion chamber, less power will be generated and the more likely for the engine to spark knock (detonate).  Adding an intercooler decreases the heat significantly, allowing for more (and cooler) air-fuel to enter the chamber for more horsepower and less detonation. 

Notes on intercooling

Intercoolers are rated by "Effectiveness" and flow restriction.  If an intercooler can take compressed air at 270 degrees, and drop it down to the cooling air temp outside the intercooler of 70 degrees (a 200 degree drop), it is 100 % Effective.  If it can only drop it half as much, from 270 degrees down to 170 degrees, it is only 50% Effective.  Air to water intercoolers with cold or ice water can be over 100% Effective.

Typically, superchargers are only used for short burst of time, 5-20 seconds or so.  Therefore, intercoolers are only needed for 5-20 seconds also.  Intercoolers have mass and are typically made from aluminum.  They posses "thermal inertia", which means if the metal is cool, it takes some time to heat it up.  This means if your intercooler is at, say 70 degrees, and you hit the throttle and boost comes up, the intercooler starts at 70 degrees and does a great job of cooling the heated, compressed air.  As the seconds tick by, the intercooler warms up.  After 5 seconds, the metal could now be 110 degrees, and it's effectiveness has been reduced.  From 5 seconds on the effectiveness may then be constant.

Intercoolers are also a flow restriction.  What good is the intercooler if it takes 10 psi of your boost pressure to force the compressed air through it?  You want an intercooler which is large enough or well designed to be free flowing.  Intercoolers can be rated by how much air flow they can pass (CFM) at some particular pressure drop (inches of water pressure).  This much like coming up with a carb's CFM rating of say 780 CFM on a flow bench.

Large intercoolers are more free flowing, have more thermal inertia, which is a good thing.  However, large intercoolers are harder to package and have more turbo lag.

Programs that take Intercooling into account

We have 3 programs that can utilized Intercooling "Effectiveness" when conducting Engine Simulation: Engine Analyzer v3.4, Engine Analyzer Plus v3.4 and Engine Analyzer Pro v3.9.  Engine Analyzer Pro also lets you specify a restriction rating.

Side Mount Intercoolers
Side Mounted Intercoolers - Image courtesy of Pacbell.net
Intercooler Chart
Intercooler Chart - Image courtesy of Pro Charger
How Intercoolers Work
How Intercoolers Work - Image courtesy of rtec.ch