s/c intercooler

[beef_bourito]

do superchargers need intercoolers? do they help? about how much of a gain can you get from one?

thank you

[burly]

Intercoolers aren't typically used with superchargers. The reason being, superchargers use a mechanical means of driving the impeller to compress incoming outside air. The turbocharger on uses exhaust gases to turn an impeller which compresses the outside air. The supercharger's mechanical means of propulsion transfers a negligible amount of heat to the incoming air charge. The turbocharger on the other hand, introduces quite a bit of heat to the incoming air charge, since the exhaust gases are extemely hot.

This is why an intercooler is typically used to increase the efficiency of a turbocharger application. The intercooler uses either an air-to-air or water-to-air system in order to remove heat from the incoming air charge. As you probably know, cold air is denser, and therefore contains more oxygen which makes combustion more efficient thereby increasing output.

Since the supercharger is not introducing any significant amount of heat to the incoming air charge, it is more important what the temperature of the incoming air is rather than what an intercooler could remove. With a supercharger application, your best bet is to use a highflow mandrel intake with a high flow airfilter placed in such a location as to intake cold ambient air, rather than hot engine bay air. This is commonly called a "cold-air intake", the benefits of which can be reaped in both naturally aspired and forced induction applications.

With this in mind, you would probably net a very negligible increase in power using an intercooler versus simply locating your superchargers intake intelligently.

Hope this helps.

[Holyterror]

I hate to contradict you, but your logic is flawed (imagine Leonard Nimoy's voice as you read).

With superchargers and turbochargers you get a hotter intake charge because of compression. While turbochargers do transfer some heat from the exhaust gas, compression is the main source of heat. It is an inescapable consequence of physics. Of course, your air conditioning works by the same token, so it's not really such a bad thing.

The reason that most supercharger applications don't use intercoolers is that superchargers usually generate a lot less boost than turbochargers. More correctly, they don't generate high boost for sustained periods. Since the s/c is tied to the crankshaft, it can only generate maximum boost at one engine speed, preferably redline. Otherwise, you can't wind the engine all the way up, or you'll destroy the s/c. Since the engine is probably going to spend a few seconds a day or less at redline, the s/c is going to be making considerably less boost most of the time. The pressure drop from an air-air intercooler makes it impractical on most s/c applications. Even turbocharged cars making less than 6-8 psi usually omit the intercooler. On a supercharged engine, that pressure drop could mean no boost through half of the tach! I guess you'd call that super lag.

High boost s/c applications do use intercoolers. In the case of these, the increased density of the intake charge makes up for the pressure loss (the whole point of the intercooler).

[Neutrino]

Simply put hollyterror is right.

[burly]

Yeah, I totally neglicted the compression.

I was, however, under the impression that supercharger's boost was controlled by the ratio of its pulley versus the crank and could use a by-pass or blowoff valve. This would mean that it could reach its max boost at a lower RPM based on the ratio, but the ratio affects the parasitic drag on the engine. This would also mean that max boost would nt necessarily be felt at redline, but could come on from RPM X the way to redline. Also, many supercharged applications on street cars have PSI ratings similiar to turbo charged engines. 10-12PSI superchargers are hardly rare.

However, compression is a large source of the heat. But, PSI for PSI, a centrifugal supercharger has a considerably cooler air charge than a turbocharger. Roots superchargers on the other hand, are closer to turbo's in air charge temp.

But yes, if you get into a very large compression application, then an intercooler will be necessary, regardless of the source of the compression. But for a centrifugal type s/c I think thats around 15-17PSI before you have any gain from an intercooler versus around 9-12PSI for turbos.

[SaabJohan]

Adiabatic efficiency is how much heat is created under compression compared to an adiabatic compression, in other words the higher the better.

A modern turbocharger can run with around 75-79% adiabatic efficiency, this is infact higher (a few points higher) than for most Vortech and similar superchargers of the centrifugal compressor type. The heat from the turbine is in other words neglectible.

Roots superchargers have a very low adiabatic efficiency, it's usually not higher than 50%. Other superchargers like the screw type has an efficiency similar to a turbochargers and centrifugal supercharger.

The only reason for not using an intercooler with a supercharger/turbocharger is because of cost or regulations. An intercooler will increase power because the cold air is denser but also decrease the thermal strain on the engine since combustion as well as exhaust temperature is decreased (this means also less NOx emissions). Today we found intercoolers even on low pressure turbos running less than 0.5 bar of boost (7 PSI). With an intercooler it's also possible to use more boost without detonation.

It's also very important to match the turbo/supercharger to an engine, if it's not correctly matched they will not work where their efficiency is best and outlet temperature is increased, and with this their power consumption is increased.

Outlet temperatures for roots (50%) and turbochargers (75%) at different boost pressures. Inlet temperature is 17 degrees C (300 K) and 1 bar, the fist value is for the roots:

0.5 bar - 88 degC - 64 degC (typical low pressure turbo)
1.0 bar - 143 degC - 101 degC (typical high pressure turbo)
2.0 bar - 229 degC - 158 degC (typical heavy truck diesel)
3.0 bar - 296 degC - 203 degC (Top Fuel dragsters)
4.0 bar - 352 degC - 240 degC (mid eighties F1 engine in qualification)

Air-air intercooler on the supercharged Koenigsegg engine. Boost pressure is 1.0 bar.

[burly]

Thats pretty slick. Thanks for the technical break down SaabJohan. So there you go beef_bourito. Between holyterror and SaabJohan, we have a pretty good understanding of how an intercooler is beneficial and how it applies to each application.

To the last part of his question "about how much of a gain can you get from one?"

If adiabatic efficiency for a centrifugal type s/c is similiar to that of a turbocharger, then I'm guessing that gain's that can be had in using an intercooler with a s/c is similar to that of a turbo as long as the additional power loss on the s/c system is similar to that in an intercooled turbo application. SaabJohan , Holyterror ?

[SaabJohan]

The gain in hp comes from the increased density if the air minus the pressure drop.

delta density = Tturbo/Tintercooler-1

Ploss = 1-P2/P1

Where P2 is the absolute pressure aftre the intercooler and P1 the absolute pressure before the intercooler.

Remember to use the right units for the temperature, according to SI that's Kelvin (degC+273,15)

The powergain by an intercooler is therefore:

delta density - Ploss

You can also use a rule of thumb by 3% gain for every 10 degC drop in temperature.