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Old 28th February 2005, 19:24   #1
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Default Turbocharge your knowledge (Learn how Turbochargers work)

I just have some basic knowledge of Turbochargers and would love to know more. However, here is some information that I know

Basics
Every engine needs air/fuel mixture to create power. The more air/fuel mixture in the cylinder, the more power it can produce. Air is sucked in from the atmosphere and mixed with fuel. The air/fuel mixture is let in through the intake valves into the cylinder. Compression and ignition occurs and the exhaust gases are let out through the exhaust valves.
Turbocharging
The exhaust gases that leave the engine are used to pump more air into the engine. There are two turbines in a turbocharger. The exhaust pipe is connected to the turbocharger. While the exhaust gases leave through the exhaust pipes, they rotate a turbine [called Turbine Wheel] in the turbocharger, the Turbine Wheel is connected to another turbine [called Compressor Wheel] which sucks in air from the atmosphere and pushes it in the engine. Since there is additional air entering the cylinder, the turbocharger may mix the appropriate additional fuel required and sends it to the engine. The extra pressure with which air is pumped into the engine is called "boost", in the sense that instead of the engine trying to suck air from the atmosphere, the turbocharger helps by forcing/pushing more air into the cylinder.

Turbocharge Loop
Once this has started, it becomes a continous loop. The more air/fuel coming from the turbocharger, helps in additional power and performance from the engine. This implies that the exhaust gases leaving the engine now, will have more force. More force at the Turbine Wheel would mean more force at the Compressor Wheel, and more air being pushed back into the cylinder. Thus, a turbocharger recycles energy.
Intercooler Turbochargers
The only problem in turbochargers is that hot air enters through the air-intake of the turbocharger. The air gets heated up because of this process. The air may become too hot so that knocking can take place. Due to which, the air will be less dense and the resulting air/fuel mixture may run leaner. To avoid such situations, an intercooler turbocharger was developed to cool the air.
Idling and Engine Type
During idling, the force of the exhaust gases is too less for the turbocharger to make any difference. The size of the engine is also important I think. Because if the engine size is too small, the exhaust gases leaving the cylinders would not have enough of force to get the best out of the turbocharger. Depending upon the engine, you get different types of Turbochargers.
Check out the following links for more information on Turbocharging:
How Does a Turbo Work?

How Turbochargers Work?


How a Turbocharger Works? - A MUST READ

Turbo Intercooler Theory: How an Intercooler works? - A MUST READ
Pic Courtesy: Turbo Calculator
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Old 28th February 2005, 20:20   #2
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Quote:
Originally Posted by Gordon
Intercooler Turbochargers
The only problem in turbochargers is that hot air enters through the air-intake of the turbocharger. The air gets heated up because of this process. The air may become too hot so that knocking can take place. Due to which, the air will be less dense and the resulting air/fuel mixture may run leaner. To avoid such situations, an intercooler turbocharger was developed to cool the air.
Little more explaination on this! Air gets heated up, when it gets compressed in the compressor. Heated air means expansion, which in turn means more volume for same air and hence, for given pressure, amount of oxygen getting inside cylinder decreases. Intercooler cools the heated air (maintaining same pressure).So now, more compressed air can get inside cylinder. Intercooler typically works between 2 stage compressors, where air is compressed in stage 1, cooled with intercooler and then again compressed in stage 2 before feeding to the cylinder.
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Old 28th February 2005, 23:45   #3
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I'd like to know a few things, since I'm getting very confused. I'm actually beginning to contradict myself ...
  • More air/fuel mixture in the cylinder means more power. But doesn't that also mean fouling??

  • Normally Aspirated Engine: Does the way exhaust gases go out of the engine affect the performance?

Quote:
Intercooler typically works between 2 stage compressors, where air is compressed in stage 1, cooled with intercooler and then again compressed in stage 2 before feeding to the cylinder.
Is that what you call a "Stage Two Turbocharger"?
If yes, that means a normal turbocharger is the one in which there is either
  • no intercooler and second stage compressors
    OR
  • no second stage compressors only.
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Old 1st March 2005, 00:14   #4
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Quote:
More air/fuel mixture in the cylinder means more power. But doesn't that also mean fouling??
No, it means more air and fuel at the right ratio in the cylinder can produce more power. For stoich ratio its about 14.7 parts of air to 1 part of fuel. So if you can stuff in more air/fuel into the cylinder keeping close to this ratio more power can be derived. But please note than 14.7 is just an indicative, ratios such as 12.8:1 etc can also derive more power... all depends on the engine, the way it acts and mods.
note that fouling is when theres an electrical leak in the plug and ground which causes failure to ignite.....


Quote:
Normally Aspirated Engine: Does the way exhaust gases go out of the engine affect the performance?
Yes it does, thats the reason we make tuned length headers. Usually when using a bad design exhaust or company manifold, on the exhaust cycle, the upward stroke pushes the burnt gasses, due to the restrictions and design in the exhaust some gasses remain in the chamber. When using tuned exhausts, these exhausts create a scavenging effect which can remove most of the unburnt gasses, which lets more fresh air fuel mixture to enter thus creating more power. But be aware exhausts should be tuned perfect to create power. Cam timing is also crucial. If the valve overlap is long and the exhaust isnt tuned according to the cam timing, valve sizes, ports etc, this can cause some of the fresh mixture entering the exhaust also.... there are tons of things which go into tuning exhausts.. i think you should get the picture....

Two stage turbos are usually twin turbo systems where two turbochargers are used. Each turbocharger is setup to produce boost at certian rpm ranges. For example turbo1 starts to produce boost from 2000rpm to 4500rpm, after which a valve opens and the second turbo also spools and starts producing more boost after 4500rpm, these systems are used to reduce turbo lag. The Supra TT uses this principle....
About the intercooler part,
well automanufacturers place the intercooler at many points. The one you have mentioned is between two cmpressors. Which is placed between two turbo's, because when the first turbo is compressing air, the air starts to generate heat due to pressures the intercooler creates a cooling effect after which this air enters the 2nd compressor. This system is rarely used nowadays. The usual setup is placing the intercooler after the compressors. This creates cooler air when entering the engine.

Hope this helped you....

Cheers
Dom
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Old 1st March 2005, 02:21   #5
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So we've finally heard form the horses mouth !!....Thanks Dom,Gordon and RXthis is very informative ...can somebody throw some light on Supercharging and the diff between turbocharging and supercharging

PS: If Supercharging topic has been discussed ealier can someone please provide me the link
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Old 1st March 2005, 09:30   #6
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Domnic, I won't say thanks yet, since there is a lot of information needed but you've helped a lot....... continue helping

Quote:
No, it means more air and fuel at the right ratio in the cylinder can produce more power. For stoich ratio its about 14.7 parts of air to 1 part of fuel. So if you can stuff in more air/fuel into the cylinder keeping close to this ratio more power can be derived. But please note than 14.7 is just an indicative, ratios such as 12.8:1 etc can also derive more power... all depends on the engine, the way it acts and mods.
note that fouling is when theres an electrical leak in the plug and ground which causes failure to ignite.....
14.7 parts of air to 1 part of fuel. Sounds familiar. Is that because normal atmospheric pressure is 14.7 psi? And at different altitudes, the air/fuel mixture can be different.

In some systems, the turbocharger itself mixes the additional fuel required to the additional air.

Does this occur after the air has passed through the intercoolers?? and how?

Normally Aspirated:
In cars that have an ECU, the computer calculates how much fuel is needed in the cylinder to counter with the amount of air entering the cylinder. In a non-ECU car, what calculates the air/fuel ratio?? The carb?? If yes, still how?

Turbocharged:
How is a turbocharger fitted on a non-ECU car?! Is this right > "On a non-ECU car, the turbocharger does not mix the additional fuel before sending the compressed air to the engine. The compressed air is directly sent to the carb where the carb understands that since there is more air coming in, more fuel must be added. So no problem."

Quote:
Yes it does, thats the reason we make tuned length headers. Usually when using a bad design exhaust or company manifold, on the exhaust cycle, the upward stroke pushes the burnt gasses, due to the restrictions and design in the exhaust some gasses remain in the chamber. When using tuned exhausts, these exhausts create a scavenging effect which can remove most of the unburnt gasses, which lets more fresh air fuel mixture to enter thus creating more power. But be aware exhausts should be tuned perfect to create power. Cam timing is also crucial. If the valve overlap is long and the exhaust isnt tuned according to the cam timing, valve sizes, ports etc, this can cause some of the fresh mixture entering the exhaust also.... there are tons of things which go into tuning exhausts.. i think you should get the picture....
Yes I get the picture, because I knew most of this before, but I've forgotten everything. When the cam is modified, it must be seen that it doesn't keep the exhaust valve open for too long. When the intake valve opens, the exhaust valve should be closed late so that most of the exhaust gases are sent out AND quickly before any air/fuel mixture flows out through the exhaust valves. It all depends on cam timing AND also if there are any restrictions to the flow of the exhaust gases. So I guess porting and polishing would be a solution for the restrictions. If too much overlap is present, it will result in wastage of fuel.

You said "Valve Sizes". Does that mean that the valve "holes" in the block can be increased in size and bigger valves can be used??

Quote:
Two stage turbos are usually twin turbo systems where two turbochargers are used. Each turbocharger is setup to produce boost at certian rpm ranges. For example turbo1 starts to produce boost from 2000rpm to 4500rpm, after which a valve opens and the second turbo also spools and starts producing more boost after 4500rpm, these systems are used to reduce turbo lag.
So in a twin turbo system, the turbo that generates power between 2000rpm - 4500rpm is a small turbocharger in size and the other is a big turbocharger in size. And after both turbochargers compress air, the air is sent for cooling at the intercoolers. Once the air is cooled down, it is sent to the cylinder.

Small turbochargers have smaller turbines and small compressors. At low rpms, the exhaust gases are enough to rotate the turbines AND give enough boost to the engine. However, at high-rpms they are not so powerful since the compressor wheel is too small to let in huge amounts of air. They have low turbo lag, because they respond faster.

Large turbochargers have bigger turbines and big compressors. At low rpms, the exhaust gases do not have enough force to rotate the turbines AND so there is no /or negligile boost provided. However, at high rpms they can produce immense boost. They suffer from turbo lag.

Quote:
can somebody throw some light on Supercharging and the diff between turbocharging and supercharging

PS: If Supercharging topic has been discussed ealier can someone please provide me the link
Supercharging will soon be discussed in another thread.
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Old 1st March 2005, 09:57   #7
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Wow, now these kind of threads(N20 and now this) are really exceptional and is very very informative especially for guys like me who is not aware of the exact processes happening..
Gordan, Domnic, Rx awesome stuff fellas, keep writing..
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Old 1st March 2005, 10:42   #8
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Wow great thread & posts now here are my doubts.

How will coller air help at high speeds ?? I as far as i remember the major difference between a Supercharger & Turbocharger is that the Turbo collects air around the exahust/headers as its hot & throws it into the engine( roughly speaking) & a Super simply pump in more air which is not so hot???

Again what I am trying to ask is how does intercooler help, i got the oxygen part but wouldn't the engine need hot/warm air at higher speeds ???

please tell
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Old 1st March 2005, 10:47   #9
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turbochraging uses exhaust gases while supercharging uses power drawn from the crank.
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Old 1st March 2005, 11:02   #10
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Well here goes....

Well atmospheric pressure does interfere with af ratios but not that if 14.7 psi is the present atmospheric pressure fuel ratio should be same. 14.7 is a stoich ratio where the oxygen and fuel at that ratio is completely burnt. But to make power different ratios are used. We ran 12.8:1 at WOT in our civic.

Please note the turbocharger does not mix anykind of fuel at all, it is a compressor(gas turbine) and nothing else. You might be talking about a draw through system. Which is used when using turbochargers with carbureted cars. This is where the carburetor is placed before the turbocharger. These kind of systems face many problems, they are prone to icing when temperaures go low at the compressor.

Non-Ecu cars are carbureted cars. A carburetor is a metering block which atomizes the fuel with the air before it reaches the cylinders. The carburetor calculates fuel ratio this way.
A predetermined size of jet is used in a carburetor which restricts the amount of fuel to a certian amount. When the throttle plate is depressed a vaccum is developed in the carburetors venturi, in which the fuel nozzle is placed in between, the vaccum generated sucks the required amount of fuel. The venturi accelerates the speed of the air which atomizes the fuel. The amount of fuel drawn depends on the vaccum and the jet size used.

Quote:
How is a turbocharger fitted on a non-ECU car?! Is this right > "On a non-ECU car, the turbocharger does not mix the additional fuel before sending the compressed air to the engine. The compressed air is directly sent to the carb where the carb understands that since there is more air coming in, more fuel must be added. So no problem
Well its more complicated than this...

Two methods are used in carbureted applications
Draw Through and Blow Through....

Draw through systems are when the carburetor is placed before the turbo, air and fuel is already mixed and then goes through the compressor.
Blow through systems, are when the turbo is placed before the carburetor. This is the most common system used when turbocharging a carbureted car. But a lot of factors have to be taken. As we know that carburetors need a vaccum to decide on the amount of fuel to be added with the air, when turbocharging a positive pressure is applied and there is no vacccum. So care should be taken to increase fuel pressure to more than the boost used otherwise the fuel will flow back from the fuel bowl. Other measures to be taken is to seal the carburetor well for pressure leaks. And more things have to be done to alter vaccum ports as we will be pressurizing the area above the throttle plate.


Quote:

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Domnic, I won't say thanks yet, since there is a lot of information needed but you've helped a lot....... continue helping

Quote:
No, it means more air and fuel at the right ratio in the cylinder can produce more power. For stoich ratio its about 14.7 parts of air to 1 part of fuel. So if you can stuff in more air/fuel into the cylinder keeping close to this ratio more power can be derived. But please note than 14.7 is just an .................................................. ......
Yes pretty correct, porting should help remove restriction and a good designed header.
by saying valve sizes i meant the size of the valve head. Not the seat dia.

Quote:
So in a twin turbo system, the turbo that generates power between 2000rpm - 4500rpm is a small turbocharger in size and the other is a big turbocharger in size. And after both turbochargers compress air, the air is sent for cooling at the intercoolers. Once the air is cooled down, it is sent to the cylinder.......................................... .
There you go you got it.... compressor sizes have a lot of factors. Each design and size have a lot of effects on the way it acts. This is why most manufacturers of turbochargers provide compressor maps so we can choose the correct turbo to match our applications.

Cheers
Dom

Last edited by Domnic : 4th March 2005 at 13:28.
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Old 1st March 2005, 11:11   #11
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to answer technocrat
Quote:
How will coller air help at high speeds ?? I as far as i remember the major difference between a Supercharger & Turbocharger is that the Turbo collects air around the exahust/headers as its hot & throws it into the engine( roughly speaking) & a Super simply pump in more air which is not so hot???

Again what I am trying to ask is how does intercooler help, i got the oxygen part but wouldn't the engine need hot/warm air at higher speeds ???
You got it all wrong... the turbocharger is a gas turbine which you can see a picture in gordons post above. The exhaust gasses are used to turn the turbine on one side of the turbo. There is another turbine which is present and is interconnected using a shaft as you can see in the picture. Once the exhaust turbine starts spinning the other turbine also starts spinning, this turbine in turn pulls in fresh air then compresses it into the engine... so note that fresh air itself is getting into the engine not hot air.... Hot air will be generated when pressures are increased (more boost) due to the high pressures the air molecules start to rapidly move due to compression and generates heat.

This is where an intercooler is used to coole the compressed air before it reaches the engine. Cooler air to the engine is always a benifit. The cold air means more dense air, so with the correct AF ratio more power can be generated.

A supercharger does not have two turbines but one. The supercharger has only the compressor part of a turbo (to make things simpler). To rotate this turbine a shaft is driven by engine itself. A pulley is added and connected to the existing fan belt system on your car. A supercharger uses different sized pulleys to either generate more or lesser boost. As boost is arrived at different rpm's of the turbine.

Cheers
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Old 1st March 2005, 11:34   #12
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Two stage turbos are usually twin turbo systems where two turbochargers are used. Each turbocharger is setup to produce boost at certian rpm ranges. For example turbo1 starts to produce boost from 2000rpm to 4500rpm, after which a valve opens and the second turbo also spools and starts producing more boost after 4500rpm, these systems are used to reduce turbo lag. The Supra TT uses this principle....

how is the speed range in which the turbocharger should operate enforced? i mean how does a turbocharger start working at 2000 rpm while another starts at 4000 rpm?

is the turbocharger is designed to operate in the region the engine is normally weak? like the 1.6 GTX is good only after 4k rpm. so a turbocharger operating from 2000-5000 rpm will increase the driveablity of the car?

what is this the difference between a turbocharger for a petrol engine and a diesel engine? is it that while the diesel engine turbocharger is designed to operate from 2000 to 5000 rpm the petrol engine turbocharger operates from 3000 to xxxx rpm?

well actually

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Old 1st March 2005, 14:20   #13
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Just to distinguish superchargers and turbochargers!

Both do same function of compressing air. The main difference between these is the way power is supplied to run the compressors.

Superchargers take the power (to compress the air) from engine output. Less efficient.
Turbocharger extract the power from hot exhaust gases. More efficient, but add backpressure on exhaust gases.
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Old 1st March 2005, 14:46   #14
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@Dom: Thanks a tonne man, it was really helpfull, got my concepts cleared now
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Old 1st March 2005, 17:20   #15
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Quote:
Originally Posted by Harrie
how is the speed range in which the turbocharger should operate enforced? i mean how does a turbocharger start working at 2000 rpm while another starts at 4000 rpm?
There are two turbochargers. One small and one big. The smaller turbocharger is directly connected to the exhaust pipes. As said earlier, smaller turbochargers can work perfectly since the force of the exhaust gases during low rpms is enough to rotate the Turbine Wheel of the turbocharger. Thus producing enough boost. However, at high-rpms the small turbocharger cannot provide enough boost. Thus at high-rpms, a valve opens that allows the exhaust gases to also go through the bigger turbocharger. Since the bigger turbocharger works perfectly at high-rpms, it provides extra boost to the engine. So you get boost at a wide range of rpm [using twin turbo] instead of only low-rpm or only high-rpm.

Quote:
what is this the difference between a turbocharger for a petrol engine and a diesel engine? is it that while the diesel engine turbocharger is designed to operate from 2000 to 5000 rpm the petrol engine turbocharger operates from 3000 to xxxx rpm?
Turbochargers for diesel and petrol engines have the same design. To know more, you must first understand the difference between a petrol and diesel engine. It is much easier to install a turbocharger on a diesel engine compared to a petrol engine due to some factors.

Also found another site where there is detailed information on Turbocharging.
http://www.turbomustangs.com/turbotech/main.htm
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