Intercoolers

01/30/93 Rev 1/23/02

5. INTERCOOLER Selection

The development of the intercooler has revolutionized high performance turbocharging in recent years. It has been particularly effective in our Turbo Regals.

The intercooler is essentially a fancy radiator that routes combustion air [hot air] through tubes that are cooled by ambient air passing over fins. This substantially cools the turbo discharge air temp. from temperatures sometimes exceeding 250 Deg.F to temperatures that can be within 20 degrees of ambient. [This is assuming that we have both an efficient turbo AND

intercooler.]

Our main objective is to cool the inlet air to the motor as much as possible. The colder the air into the motor, the denser the air charge. The higher the allowable boost level without detonation and retard AND MORE HORSEPOWER!!!

A general rule of thumb is:

· A 10-degree drop in inlet air temp charge can provide as much as 10 additional horsepower.

Our objective? Select an intercooler that will provide our motor with the COLDEST inlet air charge possible. To optimize our investment we need to answer the following questions before we make our purchase.

1. What MAJOR performance criteria must we consider?

2. What type intercooler is best suited for our performance needs?

3. How much horsepower do we want to make?

4. How much do we want to spend?

5. Do we want it to look stock?

After we have addressed the above questions we will have enough information to intelligently make the proper INTERCOOLER purchase.

5.1 What MAJOR performance criteria must we consider?

There are several parameters or specifications to be considered when selecting our INTERCOOLER but there are three[3] that are the most important.

· The pressure drop across the intercooler should be as LOW as possible.

Example: At high boost levels the stock intercooler has a pressure drop of 3# - 4# across the core. The pressure at the compressor outlet will have to be 23# - 24# for the boost at the intake manifold to equal 20# - 21#. (This higher boost level heats the air up EVEN MORE, thus increasing the heat load.)

A hi-performance, hi-efficiency intercooler usually has a pressure drop of .75# - 1.5#. The boost pressure at the turbo can be 2-3# lower yet effectively provide the same 20# - 21# boost pressure at the intake manifold.

· The temperature differential across the intercooler should be as GREAT as possible.

Example: The temperature differential of the intercooler is the inlet temperature minus the outlet temperature.

[INLET TEMP. (250 Deg.F) - OUTLET TEMP. (150 Deg.F)= 100 Delta T.]

We want the outlet temperature of the intercooler to be as cold as possible. This provides a denser air charge to the motor and allows us to run higher boost levels without detonation and retard. Thus, MORE HORSEPOWER!!!

· How much air cans the intercooler flow? How much horsepower can be supported?

The intercooler MUST be able to handle the amount of air that is required to support our horsepower goal. If the air capacity is inadequate the pressure drop across the unit [Delta-P] will increase and the temperature differential [Delta-T] across the unit will decrease. (BAD THINGS!)

Examples: A 500HP motor requires about 700 CFM of air. A 900HP motor requires 1400 CFM of air. An 1150+ HP motor requires 1700 CFM of air.

We would not want to use a stock intercooler on a 900HP engine.

Now that we have established our intercooler performance criteria, we know that we want a high capacity, low restriction, high thermal transfer unit to handle our performance needs. Now we must decide on what type of intercooler to use.

5.2 What type intercooler is best for our performance needs?

The anticipated use of our performance vehicle dictates, to some degree, what type of intercooler we should select for the most effective results.

There are two[2] main types of intercoolers:

1. Air/Air Intercoolers [See Fig.5.1]

2. Liquid Cooled Intercoolers [See Fig.5.2]

5.2.1 Air/Air Intercoolers

The air/air intercooler relies on ambient air flowing over the cooling fins to cool the combustion air. A GOOD intercooler can cool the inlet air charge to within 20 degrees of ambient.

I.e. On a 90-degree day the inlet air charge can be as low as 110 Deg.F. On a 50-degree day the inlet air charge can be a low as 70 Deg.F.

Advantages of Air/Air Intercoolers:

1. Maintenance free - Install them and forget them. The air/air requires no additional maintenance after installation.

2. Availability and Variety - There are many sizes, shapes and configurations available from many sources. The style can be tailored to a specific application.

3. Price - These are the cheapest or most economical units available. Price depends upon size and application.

4. Ease of installation.

[The Air/Air intercooler is a good choice for street or road racing performance.]

Disadvantages of Air/Air Intercoolers:

1. Inconsistency of performance - As noted earlier, the hotter the weather. The hotter the inlet air charge. The poorer the performance.

2. Long Tubing Runs - The unit is usually mounted in front of the radiator. Long tubing runs can propagate turbo lag.

Note: Great care must be exercised to insure that intercooler hoses remain intact under high boost levels.

3. Increased heat load on radiator - Since the aftermarket intercooler is usually mounted in front of the radiator, it blocks the radiator air flow. This CAN increase the engine operating temperature. However, this disadvantage can be corrected by redirecting the airflow to the radiator OR by installing a larger radiator.

5.2.2 Liquid-Cooled Intercoolers

Liquid cooled intercoolers use a source of liquid (usually water) to cool the inlet air charge. The combustion air flows through tubes and the water flows over the fins to cool the inlet air charge.

EXCEPTION ..............

The CPP liquid-cooled intercooler flows water through the tubes cooling the inlet air charge as it flows across fins.

Advantages of Liquid-Cooled Intercoolers:

1. Efficiency - Whereas the air/air units rely on ambient air to cool the inlet air charge. The liquid units rely on the coolant temperature to cool the air charge. Liquid units provide the capability to super-cool the liquid. In a high performance application, using ice and water to cool the core, the inlet air charge can be chilled BELOW 40 Deg.F on a 90-degree day! (Even COLDER charge levels can be attained using alcohol and dry ice.)

· A higher Delta-T can be attained with the liquid unit.

· A lower Delta-P can be attained with the PROPER liquid unit.

2. Performance Consistency - The liquid units are not affected by ambient temperature changes as much as the air/air units.

3. Compact Size - Since the cores are more efficient, the overall size of the unit can be significantly reduced. This makes the liquid-cooled intercooler the unit of choice for VERY high horsepower engines with space limitations.

4. Mounting Location - Most commercially available units mount in the stock location. This allows short tubing runs to and from the intercooler. This reduces turbo lag.

Since the unit is mounted BEHIND the radiator there is no obstruction of airflow to the radiator. A larger radiator or special ducting is not required.

Disadvantages of Liquid-Cooled Intercoolers:

1. Cost - Initial cost is higher than the air/air unit.

2. Ease of installation - The liquid unit is more tedious to install. The pump and reservoir requires placement and wiring.

3. Maintenance - To get MAXIMUM intercooler performance the coolant must be chilled [or iced down] between runs.

(This maintenance requirement makes the liquid unit the intercooler of choice for MAXIMUM drag racing performance.)

We have now established what type of intercooler meets our style of performance.

The answers to the following questions will help us round out the selection criteria.

5.3 How much horsepower do we want to make?

This is a very important question because it dictates the size of the intercooler core required to efficiently support our horsepower goals.

· The higher the horsepower. >> The larger the core. >> The higher the costs.

Rule #1: Establish reasonable performance goals.

Rule #2: Design all of your performance hardware to attain that goal.

You will find that your performance vehicle will be a well integrated, efficient package that will provide maximum performance for your particular level of enhancement.

If we select a unit that is too small, we are leaving performance on the table. If we select a unit that is too big, we have spent more money than we needed to.

Ask your intercooler supplier for horsepower ratings of their particular units. (Make sure that their claims are reasonable.)

5.4 How much do we want to spend?

Rule #3: Speed cost money. (This was a good place to put this.)

The appropriate axiom for this is...

Axiom #3: How fast do you want to go? How much do you want to spend?

As noted above, the larger the intercooler core the more expensive the unit. The liquid units cost more than the air/air units BUT can deliver the goods in the right application. If cost is the PRIMARY selection criteria - Go with the smaller air/air unit.

5.5 Do we want it to look stock?

There are modifications available for the stock intercooler. If you want to look stock these modifications can provide some performance improvement. One of the mod changes the inlet neck of the stock intercooler to a larger, more efficient design. Another, now popular, mod is to weld a half a core on the bottom of the stock unit. This increases the capacity by 50% yet looks stock. Note: I ran one of these for years on "Black" back in 1988.

There are also several neat HP units on the market that offer all of the above at a reasonable price and fit in stock location

Hopefully, this section has provided enough information to provide you with a systematic, educated method of selecting the type/style of intercooler that will provide the maximum performance available for our specific performance needs, at the most reasonable price.

Good Luck.