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Forced Induction/Power Adder Discuss the care and maintenance of power adders in here. Turbocharger, Supercharger and Nitrous, etc.

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Old 03-18-2008, 11:38 PM   #1 (permalink)
Join Date: Mar 2008
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Default Turbos and Superchargers, How do they work?

Some basic information regarding Turbos, Roots blowers, and Centrfigal blowers.

Superchargers: The most significant advantage to a supercharger is the simplicity of install. You don't need to plumb them into the exhaust. This also improves the reliability of the compressor, since it doesn't have to operate in the extremely hot exhaust stream. It also results in cooler intake charges since the compressor isn't soaking up heat from the exhaust-side *hot* impeller.

Because superchargers are driven from the crank, the boost they produce is proportional to engine RPM. But superchargers come in two basic varieties, centrifugal and roots. The boost curves are different for these two types.

Roots compressors are constant displacement pumps. They move the same volume of air for each rotation of the compressor assembly and airflow through the compressor varies linearly with RPM. The engine is also a constant displacement pump, it consumes the same volume of air for each rotation of the assembly. As a result, Roots compressors present the same "additional" air volume to the engine across all RPMs, which makes them good at making boost at low RPMs.

Centrifugal compressors accelerate air axially to achieve boost (which is why they're also sometimes called "axial flow compressors"). The volume of air they move is proportional to the *square* of the input RPM (it's controlled by the mV^2/r equation). This characteristic presents design challenges that don't exist for a Roots type. The centrifugal compressor has to be designed so that it won't exceed the maximum acceptable boost level at the maximum intended operating RPM. Because the boost is governed by a square-law, this means that they produces little or no boost at low RPMs.

Centrifugal compressors are more compact than Roots type. Centrifugal compressors also present less parasitic loss to the engine at low RPMs. But Roots types make better boost at low RPMs.

The "correct" choice is a function of your priorities. Roots types like Magnusson are straighforward, simple installations but you need a high-rise hood. Vortech and ATI are more complex (Vortech needs a hole in the oil pan and ATI needs plumbing for the air/air intercooler) but they fit under the factory hood.

Turbochargers: These are also axial flow compressors. They differ from Centrifugal Superchargers in that they're not driven off the crank, they use exhaust gas to spin. This makes them *much* more efficient than crank driven compressors.

Think of it in terms of "thermodynamics". The thermal energy represented by the hot exhaust is "captured" by the turbo and converted in to mechanical energy to spin the compressor. If the turbo wasn't there the exhaust energy would just flow out the tailpipe, so the boost you get from a turbo is essentially "free" (there are some parasitic losses, exhaust backpressure goes up some, for example).

But Turbo's live in the exhaust, and the exhaust get's *HOT*. This can create problems for reliability. Failures principally manifest themselves as bearing/seal failure due to buildup of abrasive "coke" on the bearings ("coke" is what's left of your oil after you cook off all the volatile components).

Besides the advantages Turbos have over Superchargers with respect to nearly nonexistent parasitic losses, they also have another key advantage. Turbos are "load sensitive". The boost the generate is proportional to the engine load NOT the engine RPM. This means that a Turbo will generally be able to produce good boost at low RPMs like a Roots, even though it's an axial flow compressor like a centrifugal type.

Intercooling: Intercooling addresses the effects that compression has on air temperature (as defined by Boyle's ideal gas law: pv=nRT). Having an intercooler is a function of the "completeness" of the design and not a function of the particular type of supercharger (Turbo or otherwise). The only thing that matters is that boost makes the intake air *hot*, and you definitely want to cool it down as much as possible before it gets to the motor.

Intercoolers come in two basic types, air-to-air and air-to-water. The debates about which type is more efficient have raged for years and will continue to rage. Assuming equal "efficiency", what it all comes down to is this... Air/Air require a large radiator up front, with long ducts/plenums to route the charge to/from the intercooler. Fitment can be a challenge, and the longer the duct work, the more boost is lost to parasitic drag. Air/water intercoolers don't need the long ductwork and they can get by with smaller radiators, but they do need plumbing for the water and a water pump.

Boost Control: When you slam the throttle closed at high RPM/Boost levels (like when you lift during a shift), all that air being pushed through the compressor (be it turbo or otherwise) suddenly has no place to go. This can cause a "compressor stall". That doesn't necessarily mean that the compressor stops spinning, it means the compressor stops compressing (think of a cavitating motor boat propeller and you'll get the idea). This is a bad thing, since the system has "inertia" and when you crack the throttle open again it takes a little while for the boost to "bounce back". Good supercharger (mechanical or turbo) designs use Blow Off Valves to address this issue. Usually just simple vacuum operated butterfly valve, BOVs provide a path to the external/ambient environment for the compressed charge air to "dump" to when the throttle is closed. This prevents a stall and improves boost response time when the throttle is next opened.

Turbochargers also have a Waste Gate. The WG is a valve that sits in the exhaust flow between the manifold and the tubro's turbine (aka "impeller"). It's pressure actuated off of the compresed-air side of the turbo. When the boost coming out of the turbo exceeds a given level (controlled by a calibrated spring inside the waste gate actuator), the waste gate valve opens and exhaust bypasses the turbine, the compressor slows and boost levels go down. This makes a Turbo self regulating. Even if it's capable of 100Lbs of boost pressure, the turbo will never boost more than the waste gate allows. This allows a turbo to be designed to produce good boost at lower loads (which are also generally lower RPMs) and not blow the top off the motor at high loads/RPMs.

However... there are tricks you can play with the waste gate and most modern turbo installations do.

An Electronic Boost Controller inserts a solenoid operated valve between the waste gate actuator and the boost-pressure side of the turbo. The valve is normally closed, so the waste gate actuator never sees any "boost" pressure at all. The boost pressure is instead sensed by an electronic transducer attached to the EBC. The EBC only opens it's solenoid valve to activate the waste gate when the boost exceeds the level set on an adjustable knob on the EBC. So long as the waste gate actuator spring is set to a level that's lower than the boost pressure selected by the EBC (a requirement of the design), the EBC is able to regulate boost pressure to any level it wants across the entire operating range. This lets you configure a Turbo (which remember is a centrifugal compressor) so that it can produce higher boosts at lower RPMs (load, actually) without having to worry that the Turbo will produce too much boost at higher RPMs (load, actually).

A mechanically driven supercharger can also use an EBC. But with a Supercharged application, the EBC regulates the opening/closing of the Blow Off Valve not the waste gate. This allows control of boost in a fashion that's similar to the Turbo EBC (except the turbo EBC regulates the source of the energy that spins the compressor, whereas a Supercharger EBC would regulate the compressed charge that goes to the motor). This allows the selection of a centrifugal compressor that could provide better boost at low RPM, without over boosting at high RPM.

Unfortunately, while there are plenty of Turbo EBCs available, Supercharger variants are much harder to come by.

(Information courtesy of RocketSled)

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Old 03-19-2008, 07:54 AM   #2 (permalink)
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That's great info Mike.
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Old 03-27-2008, 05:26 PM   #3 (permalink)
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Turbo Basics:

The mechanics of a turbocharger are closely related to the mechanics of a jet engine. If you were to modify the turbo so that the compressor outlet fed the turbine inlet you would be on your way to making a jet engine (The Junkyard Turbojet Engine - A Real Working Jet Engine Built From Junkyard Parts). A turbo's relationship with a jet engine should give you some idea of the potential of turbochargers. A turbocharger harnesses the wasted energy of exhaust gases exiting the engine to spin a turbine that compresses the intake air charge.

Exhaust gases are directed into the turbocharger through the square inlet in the exhaust housing of the turbo (shown in the bottom left of the above picture). The exhaust flows through the exhaust housing spinning the exhaust turbine. After going through the exhaust housing, the gasses flow out through the exhaust housing outlet(middle left in the picture). The turbine is connected to the compressor wheel on the intake side of the turbo through the center bearing housing. The center housing will have ports for oil to flow in to and out of to lubricate and cool the shaft, and it may or may not have ports for water to go in to and out of. The above picture does not show ports for water. Fresh air is brought into the turbocharger through the air inlet (middle right in the picture). The air is compressed by he compressor and the now pressurized air flows out through the compressor housing. Note:The picture above shows a turbocharger with an internal wastegate.

Above we see the basic layout of the components of a turbocharger system. Exhaust gases leave the engine via a turbo manifold, this replaces the stock exhaust manifold or header. One thing missing from the above diagram is an external wastegate. The wastegate is used to control boost levels by allowing exhaust gasses to bypass the turbo, thereby decreasing the volume of exhaust available to spin the turbo's turbine. In a turbo Honda, the turbocharger is bolted directly to the manifold. After moving through the turbo, exhaust gasses exit the turbo through a downpipe which connects to the rest of the exhaust system. Fresh air ,after being compressed by the turbo, passes through some intake piping and into an intercooler ('aircooler' in the above diagram). An intercooler works exactly like a radiator except pressurized air passes through it instead of water. The intercooler is mounted on the front of the car so air flows through it as the car moves down the road. This cools the pressurized intake air charge. This is necessary because when air is pressurized it heats up. Another component missing in the above diagram is a blow off valve (BOV). The blow off valve vents pressurized air when the throttle plate is closed. This prevents a pressure surge from building up in the system and possibly damaging the compressor wheel and the turbo's bearings. Another component not shown is a pop off valve (POV). Often not used on turbo Hondas, a POV is a safety valve that opens, and stays open until manually closed, when a preset boost level is reached, venting most if not all pressurized air. This prevents an overboost situation that may occur if there is a wastegate or boost controller failure.

Source:G2IC Turbo Guide - A Guide to Turbocharging your Honda / Acura Integra

This page has some really good info about the basics and then the advanced setups of turbos.

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Old 08-12-2008, 11:54 PM   #4 (permalink)
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Default the piping

my only question that i cant seem to get anwered is the piping order/route, from what i can tell i think that it goes from the air intake to the super/turbo charger to intercooler to the intake manifold/throttle body (heard it called both so not 100% sure on which one it is-- and after that it depends on if its turbo or super charger but i just cant get the intake piping issue answered-- all comments and corrections are appreciated

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Old 10-10-2008, 12:18 PM   #5 (permalink)
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You've the order correct. Air filter initially, to filter particulate and prevent it from going any further into the system, then on to the turbo where it gets sustantially heated due to 1- turbo runs off exhaust gases (typically very hot), 2- the compression that takes place in both exhaust gases and intake air and 3- hot engine oil running through keeping the turbo bearings lubricated. Everything is now super heated and not the most efficient in terms of air density. Thus it's off to the intercooler, which is simply a heat exchanger attempting to keep the air cool. Then into the engine in a slightly cooler, denser state.
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Old 10-11-2008, 12:52 PM   #6 (permalink)
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Excellent posts. Lots of good info. The only thing that I find missing is that instead of using a blow off valve and wasting all that precious compressed air, you can instead use a diverter valve. This valve is used to recirculate this air back to the compressor, also maintaining pressure in the system.

The blow off valve not only wastes potentially beneficial power that may result in lag, it also wastes fuel. The mass air flow sensor, MAF, is tricked into thinking that this air is going to be fed into the intake system and tells the computer to dump an appropriate amount of fuel to compensate. This air never makes it and the engine is temporarily "flooded." The unburned fuel will then make its way into the exhaust system and will probably explode inside the exhaust, increasing emissions and in the right applications, can create flames from the exhaust. Most blow off valves are designed to make the "pssssh" noise. A valve performing the same functions could be silent, but they wouldn't sell many. If that sound is all you want, you can buy noisemakers from ebay that fit in your exhaust to do the same thing. If you want the extra power, to save more on gas, and to keep the exhaust system safe, you might consider a diverter valve for your daily driver.
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Old 10-14-2008, 07:47 PM   #7 (permalink)
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I now know about 99% more about super and turbochargers. All I knew before was that a turbo used exhaust and a supercharger was directly driven.
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Old 09-02-2009, 05:49 PM   #8 (permalink)
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The electric types don't do anything .... Electric Supercharger Kits Turbo Super Charger Bolt On Superchargers
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Old 09-05-2009, 11:37 AM   #9 (permalink)
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I will have to chime in, anytime you compress air you get heat as a result, that is how a diesel works as a compression ignition engine. That is how an air conditioner works, when you release pressure, you get cooling. The amount of heat that the compressor on a turbo gets from the turbo physically is very minimal.
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Old 10-03-2009, 12:48 AM   #10 (permalink)
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According to Merriam-Webster's dictionary, a supercharger is defined as:
"a device (as a blower or compressor) for pressurizing the cabin of an airplane or for increasing the volume air charge of an internal combustion engine over that which would normally be drawn in through the pumping action of the pistons".
A turbocharger is defined as:
"a centrifugal blower driven by exhaust gas turbines and used to supercharge an engine".

According to Webster's, a turbocharger is included in the definition for superchargers - it is in fact a very specific type of supercharger - one that is driven by exhaust gasses. Other superchargers that do not fall into this category - the kind that we are all used to hearing about - are normally driven directly from the engine's crankshaft via a crank pulley. So in reality, it is not fair to compare all superchargers to turbochargers, because all turbochargers are also superchargers. For the purpose of this discussion, however, a supercharger will be considered all superchargers that are are not driven directly by the engine, while turbochargers will be considered all superchargers that are driven by engine exhaust gasses.

Last edited by js112; 10-06-2009 at 09:03 AM.
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