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02-11-2008, 06:09 AM
#106
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Well hopefully this will get back on track tomorrow. As there are two divergent p.o.v's we may get some clarification from both parties. Ultimately both are passionate about their beliefs but neither are stupid enough to deny new evidence either.
Ah the musings of Keyboard Warriors. We are truly today's Vikings. lol
Ah the musings of Keyboard Warriors. We are truly today's Vikings. lol
02-11-2008, 09:30 AM
#107
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All I care about it that I can get the correct amount of fuel in the cylinder for each firing event – and that amount of time decreases with RPM (sorry, its physics and I can’t change it). Other ‘bench’ stats don’t help get the right amount of fuel in.
AW is almost 100% correct in his debated statement. It needs just one caveat – you have to assume that this is a real situation and not a caulk board hypothetical – when picking the right fuel injector you need to consider the dynamic range of the injector, if we did not consider that we would all go a buy 1000 lb injectors and call it a day. It turns out that as we turn up the boost on our engines run a very wide range dynamic range of fuel requirements. If you size the injector too big it will not be able to support a decent idle. So if you choose the correct injector for the 6k rpm engine it will be too small for the 9k engine – by a lot! (for the sake of the argument we will assume that all other things – fuel pressure and boost – remain the same). At 9k RPM you only have 2/3rds of the ‘real time’ to inject the same amount of fuel that you would have at 6k RPM. If you are keeping the duty cycle at a predetermined limit (80%) then you will need a bigger injector.
OK, back to the beatings…
02-11-2008, 03:23 PM
#108
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Well something that comes out of this to me anyway is, if we can have variable vane turbos, changeable intakes, Variocam,etc in other words things that change during their use, why can't someone develop a variable injector? In other words usable at idle/low rpms and that opens up at high rpms to deliver enough fuel for that event. Or has this been tried-failed, is it possible? Seems like this would render futile the last 5 pages of this post.
02-11-2008, 03:52 PM
#109
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Well something that comes out of this to me anyway is, if we can have variable vane turbos, changeable intakes, Variocam,etc in other words things that change during their use, why can't someone develop a variable injector? In other words usable at idle/low rpms and that opens up at high rpms to deliver enough fuel for that event. Or has this been tried-failed, is it possible? Seems like this would render futile the last 5 pages of this post.
02-11-2008, 04:55 PM
#110
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Well they should be better then. I realize that they don't just send the same amount of fuel across the rpm range but someone should be able to develop a large inj that can act like the dual setup say in a Ferrari. Surely it can't be that hard....he said naively.
02-11-2008, 05:53 PM
#111
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It would be nice…
It’s a basic problem – the valve in the injector is a physical device with limitations. Due to the mass of the valve it will not react to opening durations shorter than approx 1.2ms (that’s pretty short BTW). So if your EMS sends a signal to the injector to open for less than 1.2ms the inject will not flow any fuel because it can move fast enough to respond to the signal. So if you want to have a decent idle then choose the injector sizing and fuel pressure to support a minimum turn on time of about 1.3ms.
On the other end of the scale – you need to size the injector to flow enough so that it can supply enough fuel during 80% of a firing cycle (2 revolutions) – 80% duty cycle. Actually you can surpass 80% without problems if you are careful. As we already looked at – the duration of the firing cycle decreases with RPM. So pick your max RPM, figure the cycle time and multiply by 80%...that will tell you the time limit and if you know the flow of the injector you can figure the limit due to injector capacity.
For our cars we end up with a real big dynamic range - minimum time on vs limit at max RPM/load. As you increase the power output you are increasing the dynamic range requirement of the injector. And by increasing the RPM limit you are increasing the range requirements even further. Not many other engines are in the same range.
Some EMS do offer solutions – the Electromotive EMS will allow for a second set on injectors that are managed to turn on when the first set hits 80% duty cycle. (sorry for the sales pitch!) This extends the range by a factor of two. You can have a great idle and a lot of head room at top end.
So…the problem we have is that our engines need a very minimal amount of fuel to idle (4 cylinder low rpm idle) and a lot of fuel for high boost / high RPM. Non turbo Ferraris don’t have anywhere near that range (less than half the range). I suppose the reason nobody has ever tried to produce an injector to cope with the range is that there are no ‘real’ commercial applications….just us nuts.
It’s a basic problem – the valve in the injector is a physical device with limitations. Due to the mass of the valve it will not react to opening durations shorter than approx 1.2ms (that’s pretty short BTW). So if your EMS sends a signal to the injector to open for less than 1.2ms the inject will not flow any fuel because it can move fast enough to respond to the signal. So if you want to have a decent idle then choose the injector sizing and fuel pressure to support a minimum turn on time of about 1.3ms.
On the other end of the scale – you need to size the injector to flow enough so that it can supply enough fuel during 80% of a firing cycle (2 revolutions) – 80% duty cycle. Actually you can surpass 80% without problems if you are careful. As we already looked at – the duration of the firing cycle decreases with RPM. So pick your max RPM, figure the cycle time and multiply by 80%...that will tell you the time limit and if you know the flow of the injector you can figure the limit due to injector capacity.
For our cars we end up with a real big dynamic range - minimum time on vs limit at max RPM/load. As you increase the power output you are increasing the dynamic range requirement of the injector. And by increasing the RPM limit you are increasing the range requirements even further. Not many other engines are in the same range.
Some EMS do offer solutions – the Electromotive EMS will allow for a second set on injectors that are managed to turn on when the first set hits 80% duty cycle. (sorry for the sales pitch!) This extends the range by a factor of two. You can have a great idle and a lot of head room at top end.
So…the problem we have is that our engines need a very minimal amount of fuel to idle (4 cylinder low rpm idle) and a lot of fuel for high boost / high RPM. Non turbo Ferraris don’t have anywhere near that range (less than half the range). I suppose the reason nobody has ever tried to produce an injector to cope with the range is that there are no ‘real’ commercial applications….just us nuts.
02-11-2008, 10:58 PM
#112
"""That formula you have choosen is about as accurate as a lucky guess, It does not account for RPM
500 bhp at 9000 rpm requires bigger injectors than 500 bhp @ 6000 rpm """"
The above statement is what I questioned. The DC the Injector is running at was never in question, nor was anything ever stated the injector would run at one DC. Its the statement that an engine producing 500HP would require a different size Injector if that 500 HP max was at 6000RPM or at 9000RPM. I say not.
500 bhp at 9000 rpm requires bigger injectors than 500 bhp @ 6000 rpm """"
The above statement is what I questioned. The DC the Injector is running at was never in question, nor was anything ever stated the injector would run at one DC. Its the statement that an engine producing 500HP would require a different size Injector if that 500 HP max was at 6000RPM or at 9000RPM. I say not.
02-11-2008, 11:19 PM
#113
Formula One Spin Doctor
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"""That formula you have choosen is about as accurate as a lucky guess, It does not account for RPM
500 bhp at 9000 rpm requires bigger injectors than 500 bhp @ 6000 rpm """"
The above statement is what I questioned. The DC the Injector is running at was never in question, nor was anything ever stated the injector would run at one DC. Its the statement that an engine producing 500HP would require a different size Injector if that 500 HP max was at 6000RPM or at 9000RPM. I say not.
500 bhp at 9000 rpm requires bigger injectors than 500 bhp @ 6000 rpm """"
The above statement is what I questioned. The DC the Injector is running at was never in question, nor was anything ever stated the injector would run at one DC. Its the statement that an engine producing 500HP would require a different size Injector if that 500 HP max was at 6000RPM or at 9000RPM. I say not.
Ahhaaaaa, haaaaa LOL ahh to be imprisoned
02-11-2008, 11:55 PM
#114
"""That formula you have choosen is about as accurate as a lucky guess, It does not account for RPM
500 bhp at 9000 rpm requires bigger injectors than 500 bhp @ 6000 rpm """"
The above statement is what I questioned. The DC the Injector is running at was never in question, nor was anything ever stated the injector would run at one DC. Its the statement that an engine producing 500HP would require a different size Injector if that 500 HP max was at 6000RPM or at 9000RPM. I say not.
500 bhp at 9000 rpm requires bigger injectors than 500 bhp @ 6000 rpm """"
The above statement is what I questioned. The DC the Injector is running at was never in question, nor was anything ever stated the injector would run at one DC. Its the statement that an engine producing 500HP would require a different size Injector if that 500 HP max was at 6000RPM or at 9000RPM. I say not.
I can understand the point Eniac made... that HP @ RPM is dealt with by the TQ to HP conversion equation... BUT this assumes BSFC would remain constant, which I cannot see as being the case. From memory, it was this assumption about BSFC that A.Wayne was critical of... I think he mentioned in certain applications it really needs to be determined on the dyno... otherwise it's really just a lucky guess.
I would expect BSFC to increase as you go from 6,000 to 9,000 rpm and hence I can see A.Wayne's point.
Not sure I quite follow Chris White's logic where he said:
"So if you choose the correct injector for the 6k rpm engine it will be too small for the 9k engine – by a lot! (for the sake of the argument we will assume that all other things – fuel pressure and boost – remain the same). At 9k RPM you only have 2/3rds of the ‘real time’ to inject the same amount of fuel that you would have at 6k RPM."
As, assuming the same BSFC, which he seems to be, yes, you'd only have 2/3 the real time but you'd also only need 2/3 the fuel per cycle... the net result would be identical fuel consumption (I'm not suggesting this would in fact be the case, because i content that BSFC would in fact increase).
The thing to remember here is that A.Wayne mentioned 500 HP @ 6,000 and 9,000 rpm... not 500 TQ. What Chris White said would make sense to me if we were talking about TQ at the same level for 6,000 and 9,000 rpm with BSFC remaining constant. But 500 HP @ 9,000 rpm is a lot less TQ @ 9,000 rpm than 500 HP @ 6,000 rpm is TQ @ 6,000 rpm.
Perhaps, A.Wayne will e good enough to step in and further explain what he meant... I'm asking nicely!
02-12-2008, 12:31 AM
#115
I follow your reasoning.
Why do you think it would take all of that 2/3"s time to inject enough fuel to make 500 HP. Lets say its a 4 Cyl engine. We have to inject enough to make 125 HP per Injector, 1 Injector per Cylinder understood. That number goes down as the number of Cylinders increases. As this was posted on the 944 Turbo board, I assume its a 4 Cyl engine we are discussing.
So by my calculations, an Injector that has a measured flow rate of 72 Lbs/hr at a certain FP, can not flow enough fuel in 13 msecs to make 125 HP?
I suppose we should calculate how much air mass is required to make 125 HP, then taking a typical safe AF number, calculate the fuel mass required. Then once we have this, we need to flow a Injector and measure the Injector flow at 13msecs of pulse width. I feel that an engine pumps a ceratin amount of air per intake stroke and the measured fuel requirement is based upon the air vol. Not the number of strokes. I do agree that at very high speeds opening times become a factor. Dual Injectors and the newer injector designs that flow huge volumes and run at 100% DC are used in these cases. But 9000 RPM is not anywhere high enough to warrant this factor coming into play. A 4 Cyl engine will make 125 HP per Cylinder with 13msecs of available opening time to make 500 HP. The same engine has 20msecs available to make 500 HP at 6000RPM. I see no reason why the same injector would not work for both applications. In the engines I have been around, and if we are talking about typical engines here, the VE drops as the RPM increases with many other factors causing this effect. As the VE drops, so is the demand for fuel mass. This is why the pulse time of the Injector usually lowers as the engine speed get towards the upper limit. I know there is always a exception to this, but the original statement never gave any specifics here.
Why do you think it would take all of that 2/3"s time to inject enough fuel to make 500 HP. Lets say its a 4 Cyl engine. We have to inject enough to make 125 HP per Injector, 1 Injector per Cylinder understood. That number goes down as the number of Cylinders increases. As this was posted on the 944 Turbo board, I assume its a 4 Cyl engine we are discussing.
So by my calculations, an Injector that has a measured flow rate of 72 Lbs/hr at a certain FP, can not flow enough fuel in 13 msecs to make 125 HP?
I suppose we should calculate how much air mass is required to make 125 HP, then taking a typical safe AF number, calculate the fuel mass required. Then once we have this, we need to flow a Injector and measure the Injector flow at 13msecs of pulse width. I feel that an engine pumps a ceratin amount of air per intake stroke and the measured fuel requirement is based upon the air vol. Not the number of strokes. I do agree that at very high speeds opening times become a factor. Dual Injectors and the newer injector designs that flow huge volumes and run at 100% DC are used in these cases. But 9000 RPM is not anywhere high enough to warrant this factor coming into play. A 4 Cyl engine will make 125 HP per Cylinder with 13msecs of available opening time to make 500 HP. The same engine has 20msecs available to make 500 HP at 6000RPM. I see no reason why the same injector would not work for both applications. In the engines I have been around, and if we are talking about typical engines here, the VE drops as the RPM increases with many other factors causing this effect. As the VE drops, so is the demand for fuel mass. This is why the pulse time of the Injector usually lowers as the engine speed get towards the upper limit. I know there is always a exception to this, but the original statement never gave any specifics here.
02-12-2008, 01:01 AM
#116
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Geneqco
Yes the BSFC increases at high RPM ( pumping Loses ) and more so as it now becomes very engine and application Dependant , another issue which is important and not discussed is Fuel specific gravity if tuning on C16 the BSFC will be different vs Pumpgas also air density as BSFC calculations does not compensate for humidity and density.
An engine that will use 55lbs injectors to make peak power at 6000 rpm will require larger injectors if that peak number is within 5%-10% @ 9000 rpm. even if you where to decrease the inj number( as described by grasshopper) at 9000 the injector would be at DC max with 13.3 ms vs 20 ms max @ 6000 and would be significantly leaner at 9000. Funny BSFC is a measure of engine efficiency , this ususally takes place at TQ peak , grasshopper believe's this is the point for max fuel delivery where the BSFC is at it 's most efficient point vs 9000 rpm. LOL.......
Add in the other parasitic functions of a high reving turbo engine as to heat soak , egt's vs max piston mean speed etc and you will need fuel headroom for longevity control, if via belt driven supercharger you will have to add an additional 100 bhp ( for eg. ) to your injector total in determining size, due to it's parasitic drag. So if using BSFC specific to peak BHP you would be on the small size.
In reviewing the dyno sheet previously posted you will see where peak T/Q is vs peak BHP there was a tremendous amount more fuel added after the T/Q to maintain A/FR's
In closing BSFC is used to calculate the efficiency of an engine, by backing into the BSFC by taking the max BHP on a guess , is erroneous due to the many variables involved , it can only be a ball park figure when talking about supercharged engines. ( belt or exhaust driven ) .
Run it , measure it , then talk ....
Ohhh VE tables and turbo engines
Yes the BSFC increases at high RPM ( pumping Loses ) and more so as it now becomes very engine and application Dependant , another issue which is important and not discussed is Fuel specific gravity if tuning on C16 the BSFC will be different vs Pumpgas also air density as BSFC calculations does not compensate for humidity and density.
An engine that will use 55lbs injectors to make peak power at 6000 rpm will require larger injectors if that peak number is within 5%-10% @ 9000 rpm. even if you where to decrease the inj number( as described by grasshopper) at 9000 the injector would be at DC max with 13.3 ms vs 20 ms max @ 6000 and would be significantly leaner at 9000. Funny BSFC is a measure of engine efficiency , this ususally takes place at TQ peak , grasshopper believe's this is the point for max fuel delivery where the BSFC is at it 's most efficient point vs 9000 rpm. LOL.......
Add in the other parasitic functions of a high reving turbo engine as to heat soak , egt's vs max piston mean speed etc and you will need fuel headroom for longevity control, if via belt driven supercharger you will have to add an additional 100 bhp ( for eg. ) to your injector total in determining size, due to it's parasitic drag. So if using BSFC specific to peak BHP you would be on the small size.
In reviewing the dyno sheet previously posted you will see where peak T/Q is vs peak BHP there was a tremendous amount more fuel added after the T/Q to maintain A/FR's
In closing BSFC is used to calculate the efficiency of an engine, by backing into the BSFC by taking the max BHP on a guess , is erroneous due to the many variables involved , it can only be a ball park figure when talking about supercharged engines. ( belt or exhaust driven ) .
Run it , measure it , then talk ....
Ohhh VE tables and turbo engines
Last edited by A.Wayne; 02-12-2008 at 01:44 AM.
02-12-2008, 01:44 AM
#117
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People put so much thought into injectors. Just do the rough calculations, give yourself a safe margin of error, data-log, see how it works, and if you need to make a change, then buy another set. Injectors are one of the few pleasantly inexpensive upgrades for these cars; use that to your advantage. There are better places to over-think things. My set of brand new 55lb injectors cost me $200. It's not like trying to pick a turbo, they're cheap and easy to swap.
02-12-2008, 02:23 AM
#118
Geneqco
Yes the BSFC increases at high RPM ( pumping Loses ) and more so as it now becomes very engine and application Dependant , another issue which is important and not discussed is Fuel specific gravity if tuning on C16 the BSFC will be different vs Pumpgas also air density as BSFC calculations does not compensate for humidity and density.
An engine that will use 55lbs injectors to make peak power at 6000 rpm will require larger injectors if that peak number is within 5%-10% @ 9000 rpm. even if you where to decrease the inj number( as described by grasshopper) at 9000 the injector would be at DC max with 13.3 ms vs 20 ms max @ 6000 and would be significantly leaner at 9000. Funny BSFC is a measure of engine efficiency , this ususally takes place at TQ peak , grasshopper believe's this is the point for max fuel delivery where the BSFC is at it 's most efficient point vs 9000 rpm. LOL.......
Add in the other parasitic functions of a high reving turbo engine as to heat soak , egt's vs max piston mean speed etc and you will need fuel headroom for longevity control, if via belt driven supercharger you will have to add an additional 100 bhp ( for eg. ) to your injector total in determining size, due to it's parasitic drag. So if using BSFC specific to peak BHP you would be on the small size.
In reviewing the dyno sheet previously posted you will see where peak T/Q is vs peak BHP there was a tremendous amount more fuel added after the T/Q to maintain A/FR's
In closing BSFC is used to calculate the efficiency of an engine, by backing into the BSFC by taking the max BHP on a guess , is erroneous due to the many variables involved , it can only be a ball park figure when talking about supercharged engines. ( belt or exhaust driven ) .
Run it , measure it , then talk ....
Ohhh VE tables and turbo engines
Yes the BSFC increases at high RPM ( pumping Loses ) and more so as it now becomes very engine and application Dependant , another issue which is important and not discussed is Fuel specific gravity if tuning on C16 the BSFC will be different vs Pumpgas also air density as BSFC calculations does not compensate for humidity and density.
An engine that will use 55lbs injectors to make peak power at 6000 rpm will require larger injectors if that peak number is within 5%-10% @ 9000 rpm. even if you where to decrease the inj number( as described by grasshopper) at 9000 the injector would be at DC max with 13.3 ms vs 20 ms max @ 6000 and would be significantly leaner at 9000. Funny BSFC is a measure of engine efficiency , this ususally takes place at TQ peak , grasshopper believe's this is the point for max fuel delivery where the BSFC is at it 's most efficient point vs 9000 rpm. LOL.......
Add in the other parasitic functions of a high reving turbo engine as to heat soak , egt's vs max piston mean speed etc and you will need fuel headroom for longevity control, if via belt driven supercharger you will have to add an additional 100 bhp ( for eg. ) to your injector total in determining size, due to it's parasitic drag. So if using BSFC specific to peak BHP you would be on the small size.
In reviewing the dyno sheet previously posted you will see where peak T/Q is vs peak BHP there was a tremendous amount more fuel added after the T/Q to maintain A/FR's
In closing BSFC is used to calculate the efficiency of an engine, by backing into the BSFC by taking the max BHP on a guess , is erroneous due to the many variables involved , it can only be a ball park figure when talking about supercharged engines. ( belt or exhaust driven ) .
Run it , measure it , then talk ....
Ohhh VE tables and turbo engines
I guess the approach is to try to estimate the ideal injector size "compromise" before going to the dyno and then, subject to what the dyno tells you, change it if required. Is there anything you can add that may help us to get that first selection closer to ideal than it otherwise might be?
02-12-2008, 03:28 AM
#119
I follow your reasoning.
Why do you think it would take all of that 2/3"s time to inject enough fuel to make 500 HP. Lets say its a 4 Cyl engine. We have to inject enough to make 125 HP per Injector, 1 Injector per Cylinder understood. That number goes down as the number of Cylinders increases. As this was posted on the 944 Turbo board, I assume its a 4 Cyl engine we are discussing.
So by my calculations, an Injector that has a measured flow rate of 72 Lbs/hr at a certain FP, can not flow enough fuel in 13 msecs to make 125 HP?
I suppose we should calculate how much air mass is required to make 125 HP, then taking a typical safe AF number, calculate the fuel mass required. Then once we have this, we need to flow a Injector and measure the Injector flow at 13msecs of pulse width. I feel that an engine pumps a ceratin amount of air per intake stroke and the measured fuel requirement is based upon the air vol. Not the number of strokes. I do agree that at very high speeds opening times become a factor. Dual Injectors and the newer injector designs that flow huge volumes and run at 100% DC are used in these cases. But 9000 RPM is not anywhere high enough to warrant this factor coming into play. A 4 Cyl engine will make 125 HP per Cylinder with 13msecs of available opening time to make 500 HP. The same engine has 20msecs available to make 500 HP at 6000RPM. I see no reason why the same injector would not work for both applications. In the engines I have been around, and if we are talking about typical engines here, the VE drops as the RPM increases with many other factors causing this effect. As the VE drops, so is the demand for fuel mass. This is why the pulse time of the Injector usually lowers as the engine speed get towards the upper limit. I know there is always a exception to this, but the original statement never gave any specifics here.
Why do you think it would take all of that 2/3"s time to inject enough fuel to make 500 HP. Lets say its a 4 Cyl engine. We have to inject enough to make 125 HP per Injector, 1 Injector per Cylinder understood. That number goes down as the number of Cylinders increases. As this was posted on the 944 Turbo board, I assume its a 4 Cyl engine we are discussing.
So by my calculations, an Injector that has a measured flow rate of 72 Lbs/hr at a certain FP, can not flow enough fuel in 13 msecs to make 125 HP?
I suppose we should calculate how much air mass is required to make 125 HP, then taking a typical safe AF number, calculate the fuel mass required. Then once we have this, we need to flow a Injector and measure the Injector flow at 13msecs of pulse width. I feel that an engine pumps a ceratin amount of air per intake stroke and the measured fuel requirement is based upon the air vol. Not the number of strokes. I do agree that at very high speeds opening times become a factor. Dual Injectors and the newer injector designs that flow huge volumes and run at 100% DC are used in these cases. But 9000 RPM is not anywhere high enough to warrant this factor coming into play. A 4 Cyl engine will make 125 HP per Cylinder with 13msecs of available opening time to make 500 HP. The same engine has 20msecs available to make 500 HP at 6000RPM. I see no reason why the same injector would not work for both applications. In the engines I have been around, and if we are talking about typical engines here, the VE drops as the RPM increases with many other factors causing this effect. As the VE drops, so is the demand for fuel mass. This is why the pulse time of the Injector usually lowers as the engine speed get towards the upper limit. I know there is always a exception to this, but the original statement never gave any specifics here.
02-12-2008, 09:20 AM
#120
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Not sure I quite follow Chris White's logic where he said:
"So if you choose the correct injector for the 6k rpm engine it will be too small for the 9k engine – by a lot! (for the sake of the argument we will assume that all other things – fuel pressure and boost – remain the same). At 9k RPM you only have 2/3rds of the ‘real time’ to inject the same amount of fuel that you would have at 6k RPM."
As, assuming the same BSFC, which he seems to be, yes, you'd only have 2/3 the real time but you'd also only need 2/3 the fuel per cycle... the net result would be identical fuel consumption (I'm not suggesting this would in fact be the case, because i content that BSFC would in fact increase).
"So if you choose the correct injector for the 6k rpm engine it will be too small for the 9k engine – by a lot! (for the sake of the argument we will assume that all other things – fuel pressure and boost – remain the same). At 9k RPM you only have 2/3rds of the ‘real time’ to inject the same amount of fuel that you would have at 6k RPM."
As, assuming the same BSFC, which he seems to be, yes, you'd only have 2/3 the real time but you'd also only need 2/3 the fuel per cycle... the net result would be identical fuel consumption (I'm not suggesting this would in fact be the case, because i content that BSFC would in fact increase).
I will add that in the ‘Real World’ you do need bigger injectors for the 9k engine. The ‘Real World’ is different than the paper world….