How Gtr Turbos Work

[MBS206]

If you take the RB26, and use ONE of it's turbos, the actuator still kicks in at 12PSi say, and you get x amount of air in CFM flowing through that turbo into the motor.

Now add a second turbo, feeding the RB26, the actuators still kick in at 12PSi, but now, each turbo is moving x/2 CFM of air.

Therefore, the turbo itself isn't working as hard, it isn't spinning as fast, and shouldn't be as hot.

Mind you, the motor is still receiving X amount of air, because you have two turbos, pushing X/2 amount of air... Hence

2*X/2 = X...

It's the flow of air through each turbo that drops, for the same amount of pressure.

Pressure is just the resistance of the air entering the engine... It is not a calculation of flow.

[saliya]

If an RB26 is running 12psi, is it both turbo running this boost or both running 6psi to make 12psi???

Hey,

turbos pump air (airflow); boost is a measure of the engine's resistance to airflow.

Each turbo in the stock RB26 setup is responsible for roughly half the airflow.

Each turbo's pumping potential is limited when its wastegate opens - in your

example, at 12psi. If you remove one and blank it off the other will attempt

to flow enough air for a 12psi resistance to flow (it won't be able to).

If you don't change the engine's physical characteristics (i.e. the resistance to

the airflow) then it doesn't matter how many turbochargers there are, the actual

airflow at a given pressure and temperature is the same. Because changing

a turbo _does_ change the physical characteristics it's hard to measure this.

To put it another way, if you keep the same boost, but make a GTR a single turbo

you don't lose half the airflow; and by making it a triple turbo you don't add 50% more airflow.

You don't get more airflow for free by simply adding turbos...

Regards,

Saliya

[Bumblebee]

yer u do.. u lose half the flow.

maybe not exactly half but u do lose... try making 260rwkw with 1 gtr turbo.. good luck

fact of the matter is turbos flow a certain amount of air. the bigger the compressor the more air it flows at same pressure.

hence y t88 running 30psi makes 500kw and a gt2530 running 30psi doesnt even come close.. not even with 2 of them

[cuppas]

A turbo: Exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster. -- jeremy clarkson

http://www.pureclarkson.com/jeremy-clarkson-quotes/

=D

[WRRR]

pressure does NOT = volume

pressure is pressure

volume is volume.

and WRRR is wrong. yes 2 turbos pushin 12psi is pushin twice the VOLUME of air.

Ahh not quite sunshine. try re-reading what I wrote - maybe pushing was a poor choice of word, supplying may be better.

BillyMako was asking "So 2 turbo putting out 12psi are pushing twice the amount of air into the engine than one!" I am pretty sure he means the same engine. So..

Note I said assuming the turbos have the capacity to deliver the load ie we have picked close enough the right turbo.

I'll try again still keeping it simple (lets not get into overlap etc) but the engine (any engine) has a specific swept volume that the bore and stroke form (change the definition for rotary) ie the engine displacement. For a six cylinder engine divide this by six and you get the displacement per cylinder. This doesn't change no matter what revs or pressure you throw at it (until something goes wrong and you could have infinite volume with a leg out of bed or such). So for any rpm there will be a fixed volume being presented by the engine. ie a cylinder is only filled so many times in a minute so at a fixed rpm this won't change - "required volume" which is fixed.

Now when you add pressure you are effectively increasing the amount (mass) of air being delivered to the engine not volume as that is fixed by the engine. And 12 psi is 12 psi (temperature equivalent) irrespective of the volume.

So on the same engine at the same revs one turbo, two turbos or ten turbos will still only deliver the same volume of air to the engine at a regulated 12 psi.

[Bumblebee]

lol u musta been dropped on ur head

but we'll go with what u reckon...

now, show me 1 gtr turbo making 260rwkw

if u can do it with 1.. ill retract all my statements and we'll go with urs

until then, go learn something

[WRRR]

lol u musta been dropped on ur head

but we'll go with what u reckon...

now, show me 1 gtr turbo making 260rwkw

if u can do it with 1.. ill retract all my statements and we'll go with urs

until then, go learn something

Who said anything about one GTR turbo working on its own!!!

BillyMako was asking about twin or single setups on a GTR.

I have been very carefull to state right turbo, ability to provide load, etc.

Physics is physics and what I have stated in the previous posts is correct.

A correctly sized (or oversized within reason) single, twin, triple, quadroople or what ever can will deliver the same volume and psi to an engine at the same revs if the charge temp is the same. The volume does not double or triple or whatever by adding turbos. You are regulating the system to fixed volume, regulated (fixed) pressure and temp.

Nuff said.

[Bumblebee]

no u said that 2 turbos running 12psi is the same as 1 turbo running 12psi when its not

2 turbos will supply twice the amount of air as one, hence y u cant make 260rwkw with 1 gtr turbo but u can with 2

[Bumblebee]

oh and u cant regulate volume by simply regulating boost.

like i said T88 running same boost as a turbo 1/3 of its size will supply more volume of air @ same boost

[some_cs_student]

I'm confused

WRRR, is what your trying to say, is that each cylinder has a limited capacity for air to go into it?

And that if there is say X amount of air, and your compressing it by 12psi, then its not going to matter if you add a second turbo or not?

I'm having difficulty interpreting your argument.

And the only way I know how to word this is in the form of a statement with non-realistic examples

BUT the pressure that is been referred to is referring to the turbo's ability to compress air (isn't it? I'm trying to understand this technology ), so therefore 20psi compresses more air than 10psi, assuming its the same turbo, is that correct?

However, if you have 6 turbo's running 12 psi, there's going to be more air volume wise, so therefore this air is going to get into the cylinder, is that correct?

And if it is, can you re-explain your argument again?

[WRRR]

no u said that 2 turbos running 12psi is the same as 1 turbo running 12psi when its not

2 turbos will supply twice the amount of air as one, hence y u cant make 260rwkw with 1 gtr turbo but u can with 2

I suggest you go back and calmly read what was posted and remember I am trying to keep it simple.

When at fixed rpm (ie fixed volumetric displacement) and regulated intake pressure (12 psi as was used) the volume of charge delivered to the engine is fixed. That charge can come from one, two or 10 turbos on the proviso a single one meets the corrected air flow and pressure ratio required and can be spun up by the exhaust gases to reach 12 psi and same for two/2 or three/3 or 10/10.

Just to make sure there was no probable likelihood of one std gtr turbo making 260kw I dragged out the compressor maps and it is indeed extremely unlikely and certainly not at 12psi. So you were right there but no-one was disagreeing on that and that is not what the topic is about.

As for larger turbos they do indeed deliver a larger mass flow. But the engine still has to be able to consume the air mass so that needs to be achieved by tuning - timing, fuel, air, boost, temperature, etc. or increased displacement of the engine. So for bigger hp more fuel is needed and by consequence more oxygen is need to combust the fuel. So turbos that will deliver a larger air mass are used (ie bigger). ................................

Argghhh too hard this time of night believe what you will.

[Bumblebee]

lol ur on drugs

you've not only managed to confuse me and everyone else here, but urself as well

so ur sayin that if i had X turbo supplying XY amount of air.. i could add as many turbos as i wanted to it and the engine wont take any more air in???

if thats what ur saying.. then u need sleep

[bored33]

So really, if I stick on 3 more turbos on my RB25DET (excluding the rebuild I will no doubt have afterwards ) I should make insane power. Something like this:

[MBS206]

lol ur on drugs

you've not only managed to confuse me and everyone else here, but urself as well

so ur sayin that if i had X turbo supplying XY amount of air.. i could add as many turbos as i wanted to it and the engine wont take any more air in???

if thats what ur saying.. then u need sleep

Bumbebee, STFU, what WRRR is saying IS CORRECT!

If X turbo, can supply Y amount of air, at 12PSi, and make 260RWKW, and you ADD another turbo, the ENGINE will still see Y amount of air, but each turbo will only supply Y/2 Air each.

Hence, 2 lots of Y/2 air being flowed through each turbo, makes Y amount of air entering the engine.

STFU, and stop posting, you're making this place look stupid.

[WRRR]

I'm confused

WRRR, is what your trying to say, is that each cylinder has a limited capacity for air to go into it?

And that if there is say X amount of air, and your compressing it by 12psi, then its not going to matter if you add a second turbo or not?

I'm having difficulty interpreting your argument.

And the only way I know how to word this is in the form of a statement with non-realistic examples

BUT the pressure that is been referred to is referring to the turbo's ability to compress air (isn't it? I'm trying to understand this technology ), so therefore 20psi compresses more air than 10psi, assuming its the same turbo, is that correct?

However, if you have 6 turbo's running 12 psi, there's going to be more air volume wise, so therefore this air is going to get into the cylinder, is that correct?

And if it is, can you re-explain your argument again?

Gareth

I have been trying to keep it simple. There is more to it in terms of tune, cams, compressor design, etc.

Try this analogy (I just wrote all the stuff below not knowing how to explain this simply and then this came to mind).

You have a bouncy castle it is a fixed volume to hold the shape of the castle. It takes 1000cfm of air at 12psi to keep it inflated. To stop it overinflating and bursting it has a pressure relief valve to bleed off air if it goes over 12psi. The normal inflation method is one blower that can deliver 1000cfm @ 12psi. The blower is playing up and has reduced to 800 cfm @ 12 psi so it can't keep the castle inflated. I add another blower that can deliver 800cfm @ 12psi and have to use it in parallel with the one that is playing up (second turbo). Now I have 1600 cfm going into the castle @ 12psi. What happens? The castle sounds like a whistling kettle as the blow off valve is venting 600 cfm @ 12psi. It is still only using 1000cfm @ 12psi to stay up and forces the excess air out the relief.

Think of an engine as a series of bouncy castles - @1000rpm, 2000rpm, etc

Now I'll try again but it has got wordy.

An engine in naturally aspirated form can be considered an air pump. If you take the fuel away and turn an engine over it will suck air into the cylinders to fill them (displacement), compress it and then pump it out the exhaust. The pistons only move so far in the cylinders so the volume that they provide at full stroke is fixed.

If you then put fuel into the engine at the right amount and add air (oxygen) and ignite it the burning air/fuel will create pressure which drives down the pistons turns the crank and produces mechanical power. More power requires more fuel and more air (oxygen). This can be achieved by better fuel, more displacement or more fuel and air (this is keeping it simple) or all of the above.

More fuel is relately easy, but to burn efficiently fuel needs a certain amount of oxygen. So if it is only the atmosphere and the minimal draw from the engine providing the air which contains the oxygen you have a limitation as to how much power you can generate because you can only get so much oxygen in.

But if you jam more air (and hence oxygen) in by some other means with additional fuel you can get more power than NA. Hence using a compressor to provide additional air above atmospheric.

A turbocharger is generally accepted as an exhaust gas driven compressor. It takes the exhaust gas and uses the energy (pressure, volume, heat) to turn a turbine which is connected via a shaft to another turbine that can spin and move air. To make it worthwhile the compressor turbine must move air faster than the engine's requirement for incoming combustion air as driven by the engine operating condition. ie it can produce the required volume at a pressure above atmospheric that tranlates to enough air mass (oxygen) to burn more fuel or we would just have a NA engine with a horible restriction in the intake path. It is a balance. If the compressor requires more energy to spin than is being provided by the exhaust gases or it is not providing above atmosheric contributions you are running naturally aspirated (NA) which is what is going on off boost in a turbo engine ie you don't need the power, so less fuel, so less air....

To make more exhaust gas you increase the output by increasing revs (ie more cylinders being filled and emptied per minute), increasing fuel (provides more capacity to generate power and exhaust gas) and if the operating characteristics of the turbo are right you provide more air mass to the engine to better use the additional fuel, make more power, etc. We see this positive air pressure to the engine as boost.

This boost is the manifestation of the delivery of additional air from the turbo(s) forming up against a restriction - the engine. (It is a bit like blocking the end of a hose the pressure builds up until the mains or the pump can't provide any more or you relieve the pressure by a valve or similar). ie you can't have pressure if there is not restriction of some sort.

With a turbocharger compression response is not linear with the engine requirements. A turbo takes time to build revolutions and as such air flow and then usually over delivers at high compressor speeds. As such we run pressure regulation (boost control) to not over pressure the engine and upset fuel/air etc. Over pressuring will provide more oxygen than there is fuel for normal combustion resulting in a lean mix which can result in nasty side effects.

If you design and tune an engine to produce certain power and torque responses you are playing with fuel/oxygen (air mass) loads and matching the compressor characteristics to meet your requirements for the air. So if you need 30 lb/min air mass and x fuel to generate the required power and torque this might translate to 800cfm @ atmospheric compressed to 12psi to fit into the engine (forgive me I can't remember the conversions off the top of my head). Remember the engine for given rpm is a fixed volume.

So in terms of the engine you have a fixed volume exposed per minute based on revs. You need to put in a certain mass of oxygen to burn the mass of fuel to produce the desired power and torque

Because air is compressable we can compress atmospheric air to provide a higher oxygen mass per unit volume that we can then use in the engine.

So if you have to compress 800cfm from atmospheric to 12psi to provide the required air mass (oxygen) into the engine you can do it with one or two or however many compressors. ie one that can do 800cfm from the atmoshere and compress it to say 400 cfm at double the mass (oxygen) load, or two that go from 400 cfm each to 200 each. You just have to get the combined delivery characteristics right.

The reason different turbochargers are designed is they all respond differently to exhaust energy and provide different compressor responses. Engine gurus then try to match the best response and delivery to the required duty.

So Nissan decided with the GTR to fit two smaller turbochargers that provided a lighter tubine configuration in the belief it would provide better response overall. Each of these turbochargers can generate well in excess of 12psi but can only compress enough air to deliver about 260hp each. Bigger twin replacements can deliver even more air mass but with a general trade off in pressure build response.

A larger single on a GTR can take advantage of effectively double the exhaust flow (one turbo not two) to spin a bigger ccompressor to deliver the air mass required for the engine. Argument is the turbine assembly is bigger and supposedly heavier so takes more energy to spin resulting in different pressure characteristics.

For the same power and torque outputs two turbos delivering half the volume to the required pressure each or a single providing the full volume at the same delivery pressure are doing the same job. 30 lb/min air @ 12psi is 30 lb/min @12 psi delivered by any means.

I hope this helps I really do.

[saliya]

yer u do.. u lose half the flow.

maybe not exactly half but u do lose... try making 260rwkw with 1 gtr turbo.. good luck

Hi,

You lose flow in your example - a single GTR turbo simply can't usefully flow enough air for that target HP.

But that's not what I said - I said that the amount of flow doesn't have anything to do with

the _number_ of turbos. I'm sure someone can think of a suitable single turbo that's

similar in flow and effects to the GTR twins - put that turbo on, and you'd be pressed to tell the difference.

One turbo instead of two, but the same amount of airflow (and similar HP).

fact of the matter is turbos flow a certain amount of air. the bigger the compressor the more air it flows at same pressure.

Pretty sure Boyle disagrees with you on that one...

hence y t88 running 30psi makes 500kw and a gt2530 running 30psi doesnt even come close.. not even with 2 of them

This comparison might be OK if 'all else were equal' - but it's not.

For example, are the HP measurements made at the same RPM, same exhaust backpressure, same inlet air temp?

Same motor? Same exhaust? See where I'm going?

If you express it as "flowing 75ish lb/min of air" instead of "@30psi" it's clear why a 2530 (or a pair) won't make 500kW - try looking up 75lb/min (or half that) on the GT2530's compressor map.

But I _think_ we're arguing the same thing

Regards,

Saliya

Edited November 8, 2008 by saliya

[bigmikespec]

Gareth

I have been trying to keep it simple. There is more to it in terms of tune, cams, compressor design, etc.

Try this analogy (I just wrote all the stuff below not knowing how to explain this simply and then this came to mind).

You have a bouncy castle it is a fixed volume to hold the shape of the castle. It takes 1000cfm of air at 12psi to keep it inflated. To stop it overinflating and bursting it has a pressure relief valve to bleed off air if it goes over 12psi. The normal inflation method is one blower that can deliver 1000cfm @ 12psi. The blower is playing up and has reduced to 800 cfm @ 12 psi so it can't keep the castle inflated. I add another blower that can deliver 800cfm @ 12psi and have to use it in parallel with the one that is playing up (second turbo). Now I have 1600 cfm going into the castle @ 12psi. What happens? The castle sounds like a whistling kettle as the blow off valve is venting 600 cfm @ 12psi. It is still only using 1000cfm @ 12psi to stay up and forces the excess air out the relief.

Think of an engine as a series of bouncy castles - @1000rpm, 2000rpm, etc

Now I'll try again but it has got wordy.

An engine in naturally aspirated form can be considered an air pump. If you take the fuel away and turn an engine over it will suck air into the cylinders to fill them (displacement), compress it and then pump it out the exhaust. The pistons only move so far in the cylinders so the volume that they provide at full stroke is fixed.

If you then put fuel into the engine at the right amount and add air (oxygen) and ignite it the burning air/fuel will create pressure which drives down the pistons turns the crank and produces mechanical power. More power requires more fuel and more air (oxygen). This can be achieved by better fuel, more displacement or more fuel and air (this is keeping it simple) or all of the above.

More fuel is relately easy, but to burn efficiently fuel needs a certain amount of oxygen. So if it is only the atmosphere and the minimal draw from the engine providing the air which contains the oxygen you have a limitation as to how much power you can generate because you can only get so much oxygen in.

But if you jam more air (and hence oxygen) in by some other means with additional fuel you can get more power than NA. Hence using a compressor to provide additional air above atmospheric.

A turbocharger is generally accepted as an exhaust gas driven compressor. It takes the exhaust gas and uses the energy (pressure, volume, heat) to turn a turbine which is connected via a shaft to another turbine that can spin and move air. To make it worthwhile the compressor turbine must move air faster than the engine's requirement for incoming combustion air as driven by the engine operating condition. ie it can produce the required volume at a pressure above atmospheric that tranlates to enough air mass (oxygen) to burn more fuel or we would just have a NA engine with a horible restriction in the intake path. It is a balance. If the compressor requires more energy to spin than is being provided by the exhaust gases or it is not providing above atmosheric contributions you are running naturally aspirated (NA) which is what is going on off boost in a turbo engine ie you don't need the power, so less fuel, so less air....

To make more exhaust gas you increase the output by increasing revs (ie more cylinders being filled and emptied per minute), increasing fuel (provides more capacity to generate power and exhaust gas) and if the operating characteristics of the turbo are right you provide more air mass to the engine to better use the additional fuel, make more power, etc. We see this positive air pressure to the engine as boost.

This boost is the manifestation of the delivery of additional air from the turbo(s) forming up against a restriction - the engine. (It is a bit like blocking the end of a hose the pressure builds up until the mains or the pump can't provide any more or you relieve the pressure by a valve or similar). ie you can't have pressure if there is not restriction of some sort.

With a turbocharger compression response is not linear with the engine requirements. A turbo takes time to build revolutions and as such air flow and then usually over delivers at high compressor speeds. As such we run pressure regulation (boost control) to not over pressure the engine and upset fuel/air etc. Over pressuring will provide more oxygen than there is fuel for normal combustion resulting in a lean mix which can result in nasty side effects.

If you design and tune an engine to produce certain power and torque responses you are playing with fuel/oxygen (air mass) loads and matching the compressor characteristics to meet your requirements for the air. So if you need 30 lb/min air mass and x fuel to generate the required power and torque this might translate to 800cfm @ atmospheric compressed to 12psi to fit into the engine (forgive me I can't remember the conversions off the top of my head). Remember the engine for given rpm is a fixed volume.

So in terms of the engine you have a fixed volume exposed per minute based on revs. You need to put in a certain mass of oxygen to burn the mass of fuel to produce the desired power and torque

Because air is compressable we can compress atmospheric air to provide a higher oxygen mass per unit volume that we can then use in the engine.

So if you have to compress 800cfm from atmospheric to 12psi to provide the required air mass (oxygen) into the engine you can do it with one or two or however many compressors. ie one that can do 800cfm from the atmoshere and compress it to say 400 cfm at double the mass (oxygen) load, or two that go from 400 cfm each to 200 each. You just have to get the combined delivery characteristics right.

The reason different turbochargers are designed is they all respond differently to exhaust energy and provide different compressor responses. Engine gurus then try to match the best response and delivery to the required duty.

So Nissan decided with the GTR to fit two smaller turbochargers that provided a lighter tubine configuration in the belief it would provide better response overall. Each of these turbochargers can generate well in excess of 12psi but can only compress enough air to deliver about 260hp each. Bigger twin replacements can deliver even more air mass but with a general trade off in pressure build response.

A larger single on a GTR can take advantage of effectively double the exhaust flow (one turbo not two) to spin a bigger ccompressor to deliver the air mass required for the engine. Argument is the turbine assembly is bigger and supposedly heavier so takes more energy to spin resulting in different pressure characteristics.

For the same power and torque outputs two turbos delivering half the volume to the required pressure each or a single providing the full volume at the same delivery pressure are doing the same job. 30 lb/min air @ 12psi is 30 lb/min @12 psi delivered by any means.

I hope this helps I really do.

WOW!!!!!!!!! You are patient! Is your name Jebus?

[Kranker]

Not only is WRRR patient and knowledgeable, but he didnt even respond to bumblebee's childish slander and name calling

...must be Jebus

[WRRR]

Thnaks guys.

Result of a quiet night and trying to help someone who was asking a genuine question.

These forums are only as good as the people on them and the accuracy of the information shared. SAU has been very good to me and I have learnt heaps of little tricks and saved a small forture (if you can do that with a GTR).

Karma.

[Shakiel]

Always come back to the forums for a good laugh