Intercooled Vs. Non-Intercooler

There has been many debates between the issue of intercooling and non-intercooling.  Here are some facts based on Corky Bell's book called Supercharged!.  Here is some interesting information you should considered when you plan to get a forced induction system.

Before we start, here are some legends you should understand:
+ = Plus or Sum
- = Minus
x = Multiply
/ = Divide

Here are some formulas will be useful:

Desired Power = stock power x pressure ratio x density ratio x volumetric efficiencies ratio x drive power efficiency

Volumetric Efficiencies = supercharger volumetric efficiencies / engine volumetric efficiencies

Pressure Ratio = desired power / existing power or
                             desired power / stock power x pressure ratio x density ratio x volumetric efficiencies ratio x drive power efficiency

 

Density Ratio = original absolute temperature / find absolute temperature
Root:
Non-Intercooled = 460degrees + 90 degrees / 460 degrees + 200 = .83
Intercooled = 460degrees + 90 degrees / 460 degrees + 107 = .97

Centrifugal:
Non-Intercooled = 460degrees + 90 degrees / 460 degrees + 170 = .87
Intercooled = 460degrees + 90 degrees / 460 degrees + 102 = .98

Density Ratio Non-Intercooled Intercooled
Root Supercharger .83 .97
Centrifugal .87 .98

Lets plug in some numbers and make it real.  Now we will be using our first generation 1UZFE.  A car is rated at 220 bhp and our desired bhp will be 300.  Lets use these formulas and see how it will affect the outcome between intercooling and non-intercooling.  The below table show amount of boost require to achieve 300 bhp

Type Non-Intercooled Intercooled
Root 10.1 psi 6.3 psi
Centrifugal 7.2 psi 4.7 psi

What the above table saying is that for a 220 bhp to make 300 bhp.  It would take a 10.1 psi in a non-intercooled root style supercharger system to make 300 bhp in the same intake/chamber temperature as a 4.7 psi intercooled Centrifugal supercharger system.  In another word, it will take a 10.1 psi from a root style supercharger to make the same power as a intercooled 4.7 psi from a Centrifugal Supercharger system.

Here is an database that I have complied using 250 bhp as our stock horsepower and comparing Root supercharger and Centrifugal along with intercooling.  The boost require for a intercooler Centrifugal system to make 400 bhp would be around 6.6 psi vs. non-intercooled Root Style 12.52 psi.  The below data is calculated using Corky Bell's book and formulas.

     
250 bhp base hp Root Style Supercharger   Centrifugal Supercharger
Desired bhp Boost Non-Intercooled Boost Intercooled Boost Non-Intercooled Boost Intercooled
300 bhp 5.7575 psi 2.793 psi 3.3222 psi 1.29999891 psi
325 bhp 7.448 psi 4.263 psi 4.82454 psi 2.63333301 psi
350 bhp 9.1385 psi 5.8065 psi 6.326733 psi 3.966648 psi
375 bhp 10.829 psi 7.301 psi 7.829024 psi 5.30000121 psi
400 bhp 12.5195 psi 8.80775 psi 9.3312905 psi 6.63333531 psi
425 bhp 14.21 psi 10.3145 psi 10.833557 psi 7.96666941 psi
450 bhp 15.9005 psi 11.82125 psi 12.3358235 psi 9.30000351 psi
475 bhp 17.591 psi 13.328 psi 13.83809 psi 10.63333761 psi
500 bhp 19.2815 psi 14.83475 psi 15.3403565 psi 11.96667171 psi
525 bhp 20.972 psi 16.3415 psi 16.842623 psi 13.30000581 psi
550 bhp 22.6625 psi 17.84825 psi 18.3448895 psi 14.63333991 psi
575 bhp 24.353 psi 19.355 psi 19.847156 psi 15.96667401 psi
600 bhp 26.0435 psi 20.86175 psi 21.3494225 psi 17.30000811 psi
625 bhp 27.734 psi 22.3685 psi 22.851689 psi 18.63334221 psi
650 bhp 29.4245 psi 23.87525 psi 24.3539555 psi 19.96667631 psi
675 bhp 31.115 psi 25.382 psi 25.856222 psi 21.30001041 psi
700 bhp 32.8055 psi 26.88875 psi 27.3584885 psi 22.63334451 psi
725 bhp 34.496 psi 28.3955 psi 28.860755 psi 23.96667861 psi
750 bhp 36.1865 psi 29.90225 psi 30.3630215 psi 25.30001271 psi
775 bhp 37.877 psi 31.409 psi 31.865288 psi 26.63334681 psi
800 bhp 39.5675 psi 32.91575 psi 33.3675545 psi 27.96668091 psi

Full data from Excel Spread Sheet Boost Calculation and Pressure Ratio

Pressure Ratio = desired power / existing power
PR = 400 / 250 = 1.6  The pressure ratio can tell us the boost pressure needed, as pressure ratio of 1.60 mean that the boost pressure is .60 of an atmosphere above atmospheric pressure of 14.7 psi. 
Boost = .60 x 14.7 psi = 8.82 psi that would be intercooled root style supercharger.

Density Ratio = original absolute temperature / find absolute temperature
In order to begin our density ratio, we need to know about each type of supercharger and its thermal efficiency.  Here are the comparison of three popular type of superchargers:
 

Type Et (%) Temp increase with 1 psi
Roots 55 18.5
Screw 70 14.6
Centrifugal 75 13.6
Turbocharger 75 ???

Here is what Corky have to say about intercooling: "The intercooler can rescue this bad temperature situation.  Let's look at the whole picture again when we place an intercooler between the supercharger and the engine.  Assume the intercooler will remove 85% of the temperature put in by the supercharger.

To calculate the final intercooled chamber temperatures, we use the same procedure as in the previous section, inserting the intercooled temperature gains from in the temperature formula for a 9:1 compression ratio.  This shows that with intercooling, we can run substantially higher boost before reaching the arbitrary 1075 degrees limit: about 10 psi for roots and 13 psi for centrifugal and twin screw.

Although this exercise in numbers is full of approximation, its easy to show, for example, that you can run 40 psi boost intercooled at the same chamber temperature as 8 psi non-intercooled".

Here is an extreme comparison between low thermal efficient and high thermal efficient supercharger.  Secondly, we also compare a non-intercooled root style supercharger with intercooled centrifugal supercharger.

Non-intercooled root style supercharger Vs. a intercooled centrifugal supercharger

Type of Supercharger Non-Intercooled @ 10 psi Intercooled @ 10 psi
Root 130 Degrees F 17 Degrees F
Centrifugal 90 Degrees F 13 Degrees F

 

Below are the comparison between intercooled Centrifugal and Root Style Supercharger and along with non-intercooled.

 

If you compare a non-intercooler root style at 10 psi vs. a intercooler centrifugal at 10 psi is 130 degrees F to 13 degrees F.  Its also 100 degrees difference at 10 psi.  The above data is from Supercharged! book page 40 and 42 ISBN 0-8376-0168-1

 

 

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