How does a turbo work ?
Discussion
aeropilot said:
And of course there's also a 'twin-scroll' turbo which some people mistakenly think are twin turbos.....
Er yeah. All twin scroll does it seperate the exhaust pulses from the manifold all the way to the turbine, for slightly reduced lag and slightly higher power.Then we have roller bearing core turbos, which reduce lag and spool up more by reducing internal friction.
Gazboy said:
It's an absolute arseache to get compound (big and a small) turbocharging to work so I'm suprised BMW went with this approach.
and that's why I remember thinking it was a bit bonkers when it came out...However I just found this on the BMW site, so maybe your right, seriously confused now...
BMW Website said:
The six-cylinder petrol engine with Twin Turbo.
Athleticism and efficiency go hand in hand - as our new six-cylinder petrol engine proves. Thanks to High-precision Direct Injection, it gets the most out of every drop of fuel. HPDI sends a cloud of precisely blended fuel/air mixture to the spark plug, where it is surrounded by colder air. Combined with the benefits of twin turbo technology, it makes for greater refinement, better performance and lower fuel consumption. By using two small turbochargers instead of a single large one, the twin turbo system ensures boost is available right across the rev range.
ETAAthleticism and efficiency go hand in hand - as our new six-cylinder petrol engine proves. Thanks to High-precision Direct Injection, it gets the most out of every drop of fuel. HPDI sends a cloud of precisely blended fuel/air mixture to the spark plug, where it is surrounded by colder air. Combined with the benefits of twin turbo technology, it makes for greater refinement, better performance and lower fuel consumption. By using two small turbochargers instead of a single large one, the twin turbo system ensures boost is available right across the rev range.
another website said:
I previously mentioned the engine will have it’s two turbos in sequential form, so I apologize for the mis-information. The twin-turbo system is actually in-line, with a turbo being fed by 3 cylinders each. Two smaller turbos alllow a much faster spooling time than 1 big turbo.
Starting to look like I'm rather wrong in that case...EVO said:
This decided, BMW then set about the task of producing an engine that possessed all the increased performance gains of forced induction whilst retaining the qualities of the best naturally aspirated engines. As a result there are two small low-inertia turbos, each one doing its stuff on three cylinders while keeping lag to an absolute minimum.
High-precision injection was also seen as vital to the reintroduction of turbos to BMW petrol engines. Accordingly, piezo injectors have been employed for their ability to provide very accurate fuel delivery, meaning greater fuel efficiency - something BMW is starting to take very seriously - without compromising performance.
I'll get back in my box...High-precision injection was also seen as vital to the reintroduction of turbos to BMW petrol engines. Accordingly, piezo injectors have been employed for their ability to provide very accurate fuel delivery, meaning greater fuel efficiency - something BMW is starting to take very seriously - without compromising performance.
Edited by AngryS3Owner on Friday 18th April 16:48
Heh - well I'll just removed the twin turbo badge off my 3000GT then shall I?
nats1rt said:
Silent1 said:
Twin turbos get around this by having a very small turbo that kicks in whilst the bigger turbo is still going too slow to be useful.
Sorry if that's too simple
Twin turbo.Sorry if that's too simple
MarkK said:
But not on the 3000GT/GTO - they are on each bank of the V and the same size, they aren't sequential. Relatively small turbos though so lag is minimal.
Bi-turbo.there is no specific difference between twin turbo or bi-turbo. It's like saying inline six or straight six as an engine configuration.
There are two kinds of twin (bi!) turbos. Sequential or Independent.
Sequential uses a small turbo for low rev power, as smaller turbos spin up faster, meaning you get on boost quicker. However, small turbos can only pump smaller amounts of air, meaning they are no good for big power. This is why a second, larger turbo is plumbed in, which is normally blocked off from the exhaust gases at low engine speeds, but is activated once the smaller turbo begins to run out of puff.
Yes, it was a b
d to engineer, I suspect. This sort of turbo system is found in the BMW X35D (diesel) engines.
independent turbos have two turbos the same size, each of which are attached to half the total about of cylinders. So a 6 cylinder engine would have three of the cylinders blowing into one turbo, and three of the cylinders blowing into another. This allows quick spool up of the turbos, and relatively high powers. It is also a hell of a lot easier to engineer that a sequential turbo system.
These sort of turbo systems are found in the new GTR for example, and the BMW X35i (petrol) engines.
independent twin turbos are very popular in V formation engines, as you avoid some difficult plumbing getting both banks of exhaust gasses to the same place. Instead, you simply have one turbo per bank.
below is a picture of quad independent turbos for an Evo! It's a bit OTT, but gives a good clear idea of how independent turbos work!
There are two kinds of twin (bi!) turbos. Sequential or Independent.
Sequential uses a small turbo for low rev power, as smaller turbos spin up faster, meaning you get on boost quicker. However, small turbos can only pump smaller amounts of air, meaning they are no good for big power. This is why a second, larger turbo is plumbed in, which is normally blocked off from the exhaust gases at low engine speeds, but is activated once the smaller turbo begins to run out of puff.
Yes, it was a b
d to engineer, I suspect. This sort of turbo system is found in the BMW X35D (diesel) engines.independent turbos have two turbos the same size, each of which are attached to half the total about of cylinders. So a 6 cylinder engine would have three of the cylinders blowing into one turbo, and three of the cylinders blowing into another. This allows quick spool up of the turbos, and relatively high powers. It is also a hell of a lot easier to engineer that a sequential turbo system.
These sort of turbo systems are found in the new GTR for example, and the BMW X35i (petrol) engines.
independent twin turbos are very popular in V formation engines, as you avoid some difficult plumbing getting both banks of exhaust gasses to the same place. Instead, you simply have one turbo per bank.
below is a picture of quad independent turbos for an Evo! It's a bit OTT, but gives a good clear idea of how independent turbos work!
Silent1 you ought to be a teacher, that was a explanation right at the correct level. The guy says English isn't his first language and the engineers come out with 5-syllable technical words.
My favourite explanation - first understand how a supercharger works. This is like sticking a hairdryer into your mouth to get more air into your lungs
The supercharger blower is driven, usually by a belt, off the crankshaft of the engine, eating some of the power that would normally drive the wheels (the engineers will call this 'parasitic drag' but let's keep it simple).
The turbo does the same thing - blows more air into the engine so you can burn more fuel and get a bigger bang. The difference is that the blower is driven by *waste energy* - the heat in the exhaust gas. As the exhaust expands out of the cylinder, some of this force can be used on the 'hot' side of the turbo to drive the blower.
Superchargers do the same thing as turbochargers - turbochargers are more efficient (since they are using 'waste energy' to power them) but you can get lag (when there's not enough exhaust to spin the blower hard enough), whereas a supercharger is directly driven from the crankshaft and gives instant power.
Things get complicated with multiple turbos mainly because of plumbing and the desire to have all cylinders of an engine operating at the same power (having 3 cylinders pumping hard with turbo boost, and the other three pumping normally because the turbo isn't working, is a recipe for a broken engine). Thus multiple turbos have to be centrally controlled to ensure they pump the right amount of gas to the right place.
You also need to ensure the pipework involved is as short as possible, otherwise the delay between hitting the throttle, more exhaust gas spinning up the turbo, the turbo pumping more air into the induction system (which may be long, with an intercooler to cool down the hot gas coming out of the turbo), and then that extra air getting into the engine, can be long. This delay is the famous turbo lag. There's that famous picture of an American V8 with 8 separate turbos, each separated from the exhaust port and the induction by long piping... that thing must have lag like hell (relatively speaking, I'm sure it's got decent torque to start with, being a big block V8)
My favourite explanation - first understand how a supercharger works. This is like sticking a hairdryer into your mouth to get more air into your lungs
The supercharger blower is driven, usually by a belt, off the crankshaft of the engine, eating some of the power that would normally drive the wheels (the engineers will call this 'parasitic drag' but let's keep it simple).The turbo does the same thing - blows more air into the engine so you can burn more fuel and get a bigger bang. The difference is that the blower is driven by *waste energy* - the heat in the exhaust gas. As the exhaust expands out of the cylinder, some of this force can be used on the 'hot' side of the turbo to drive the blower.
Superchargers do the same thing as turbochargers - turbochargers are more efficient (since they are using 'waste energy' to power them) but you can get lag (when there's not enough exhaust to spin the blower hard enough), whereas a supercharger is directly driven from the crankshaft and gives instant power.
Things get complicated with multiple turbos mainly because of plumbing and the desire to have all cylinders of an engine operating at the same power (having 3 cylinders pumping hard with turbo boost, and the other three pumping normally because the turbo isn't working, is a recipe for a broken engine). Thus multiple turbos have to be centrally controlled to ensure they pump the right amount of gas to the right place.
You also need to ensure the pipework involved is as short as possible, otherwise the delay between hitting the throttle, more exhaust gas spinning up the turbo, the turbo pumping more air into the induction system (which may be long, with an intercooler to cool down the hot gas coming out of the turbo), and then that extra air getting into the engine, can be long. This delay is the famous turbo lag. There's that famous picture of an American V8 with 8 separate turbos, each separated from the exhaust port and the induction by long piping... that thing must have lag like hell (relatively speaking, I'm sure it's got decent torque to start with, being a big block V8)
AngryS3Owner said:
Gazboy said:
It's an absolute arseache to get compound (big and a small) turbocharging to work so I'm suprised BMW went with this approach.
and that's why I remember thinking it was a bit bonkers when it came out...However I just found this on the BMW site, so maybe your right, seriously confused now...
BMW Website said:
The six-cylinder petrol engine with Twin Turbo.
Athleticism and efficiency go hand in hand - as our new six-cylinder petrol engine proves. Thanks to High-precision Direct Injection, it gets the most out of every drop of fuel. HPDI sends a cloud of precisely blended fuel/air mixture to the spark plug, where it is surrounded by colder air. Combined with the benefits of twin turbo technology, it makes for greater refinement, better performance and lower fuel consumption. By using two small turbochargers instead of a single large one, the twin turbo system ensures boost is available right across the rev range.
ETAAthleticism and efficiency go hand in hand - as our new six-cylinder petrol engine proves. Thanks to High-precision Direct Injection, it gets the most out of every drop of fuel. HPDI sends a cloud of precisely blended fuel/air mixture to the spark plug, where it is surrounded by colder air. Combined with the benefits of twin turbo technology, it makes for greater refinement, better performance and lower fuel consumption. By using two small turbochargers instead of a single large one, the twin turbo system ensures boost is available right across the rev range.
another website said:
I previously mentioned the engine will have it’s two turbos in sequential form, so I apologize for the mis-information. The twin-turbo system is actually in-line, with a turbo being fed by 3 cylinders each. Two smaller turbos alllow a much faster spooling time than 1 big turbo.
Starting to look like I'm rather wrong in that case...EVO said:
This decided, BMW then set about the task of producing an engine that possessed all the increased performance gains of forced induction whilst retaining the qualities of the best naturally aspirated engines. As a result there are two small low-inertia turbos, each one doing its stuff on three cylinders while keeping lag to an absolute minimum.
High-precision injection was also seen as vital to the reintroduction of turbos to BMW petrol engines. Accordingly, piezo injectors have been employed for their ability to provide very accurate fuel delivery, meaning greater fuel efficiency - something BMW is starting to take very seriously - without compromising performance.
I'll get back in my box...High-precision injection was also seen as vital to the reintroduction of turbos to BMW petrol engines. Accordingly, piezo injectors have been employed for their ability to provide very accurate fuel delivery, meaning greater fuel efficiency - something BMW is starting to take very seriously - without compromising performance.
Edited by AngryS3Owner on Friday 18th April 16:48
Road_Terrorist said:
The final example, which is extremely rare for road cars but common on aircraft, (and the odd diesel) is series, or staged, turbocharging where you basically have one turbo blowing into another one, which is mainly useful at high altitudes where the air is thin and needs to be compressed to very high pressure levels.
Some tractor pulling rigs have FIVE stages of this 
AngryS3Owner said:
Road_Terrorist said:
The example of small turbo and large turbo is called Sequential Twin Turbo, this is a relatively rare setup as it's quite complicated, being used on a only a few production vehicles, the only ones I can think of off the top of my head are the Mazda FD RX7, Toyota Supra TT MkIV, Porsche 959, Subaru Legacy B4 and Mazda JC Cosmo.
I'm starting to think everyone just ignores what I write, ah well nevermind 
All the new BMW *35i engines are sequential twin turbos.
ETA: I should have read page 2 before replying but the picture is useful.
Edited by mackie1 on Friday 10th April 09:47
Road_Terrorist said:
nats1rt said:
Silent1 said:
Twin turbos get around this by having a very small turbo that kicks in whilst the bigger turbo is still going too slow to be useful.
Sorry if that's too simple
Twin turbo.Sorry if that's too simple
MarkK said:
But not on the 3000GT/GTO - they are on each bank of the V and the same size, they aren't sequential. Relatively small turbos though so lag is minimal.
Bi-turbo.To break it down:
The example of small turbo and large turbo is called Sequential Twin Turbo, this is a relatively rare setup as it's quite complicated, being used on a only a few production vehicles, the only ones I can think of off the top of my head are the Mazda FD RX7
Andy
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