LINK Standalone.
02-08-2008, 12:22 PM
#77
Formula One Spin Doctor
Rennlist Member
Rennlist Member
Not sure , if you are addressing me, if so you are using words and descriptions i don't understand, like pintle ? BSFC ?availbelat teh higher speeds ? what do you mean by availbelat teh? What do you mean by less fuel after peak T/Q ? turbo or n/a
just to clarify are you saying after the peak T/Q shown , i should have less fuel for peak HP at 9000 RPM , Please clarify , i'm really interested in your take on this .
Thanks in advance
just to clarify are you saying after the peak T/Q shown , i should have less fuel for peak HP at 9000 RPM , Please clarify , i'm really interested in your take on this .
Thanks in advance
Last edited by A.Wayne; 02-08-2008 at 12:57 PM.
02-09-2008, 02:26 AM
#79
Rennlist Member
Thread Starter
So to clarify for the dummies (me) if we say the inj are firing for a much shorter duration at high rpms due to the speed that everything is happening, we could assume that we need less fuel then. Yet because we are spinning at max rpms we should possibly need more fuel or we'll have starvation. So if they're firing for a shorter duration yet that duration comes around faster the more rpms, then might we still need a lot of fuel? Did that make sense?
02-09-2008, 12:08 PM
#80
Burning Brakes
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So to clarify for the dummies (me) if we say the inj are firing for a much shorter duration at high rpms due to the speed that everything is happening, we could assume that we need less fuel then. Yet because we are spinning at max rpms we should possibly need more fuel or we'll have starvation. So if they're firing for a shorter duration yet that duration comes around faster the more rpms, then might we still need a lot of fuel? Did that make sense?
What that right amount of fuel is depends on the volume (mass) of air that is coming into the engine on that combustion event. Not the one before or the one after. So as your boost varies, as your volumetric efficiencies vary, as your rpm varies, then the ECU and the injector have to be able to inject the amount of fuel necessary to keep the air to fuel ratio in the target zone you want. That may be for max fuel economy, or it may be for max power, or it may be for best emissions.
So as the rpm climbs and typically the amount of air ingested goes up the injector has to be able to efficiently inject the amount of fuel required. the time available does go down so the injector has less time to inject X cc's of fuel. How much is X depends on all of the above factors. For a really efficient head and on an engine that the torque curve keeps climbing then my thoughts are the injectors will have to continue to inject more and more fuel in a shorter and shorter time.
If the torque curve falls off then the peak fuel requirement is past (assuming all other factors equal) so the injectors can inject slightly less per combustion event but it is done more often per minute so the HP can continue to climb.
For any engine there is an overall efficiency factor called BSFC or brake specific fuel consumption. This is stated as so many lbs mass of fuel per horsepower hour. So if the engine is running for an hour at its peak horsepower it would consume X lbs mass of fuel. Regardless of what RPM that engine is running, the injectors need to be able to properly atomize and flow enough to keep the AFRs in the desired range.
Just my take on what the injector needs to do.
02-10-2008, 04:55 PM
#81
Ok, I'm back. Sorry about that. I had a short trip to take. Also, my spelling is poor, or should I say, my keyboard control.
To go back to the original comment that drew my attention, why does an Injector need to be bigger for 500HP at 9000 RPM than it needs to be for 500HP at 6000 RPM? Injector sizing is based upon the air volume the engine injests, per stroke, not its RPM. The reason the fuel demand goes down at higher speeds is the valve event time is less. Less time for the Intake valve to be open requires less fuel to maintain the same AF number. The biggest fuel demand is at peak torque where the engine is most efficient. This is why when logging the AF trace, there is always a dip at peak torque. Look at the Injection pulse times at the higher speeds. They will always be less that at peak torque.
500 HP at 6000 RPM will require the same Injector size as 500 HP at 9000 RPM. Given these are peak HP numbers. If we make some assumptions here based upon what the poster stated, we could say the 6000 RPM engine must make somewhere close to 500 units of Torque, unless the VE of this engine just drops thro the floor in 800 RPM. On the other hand we cannot make this same assumption on the 9000 RPm engine. The torque curve could be very broad and the peak torque could be close to 500 units as in the case of the 6000 RPM engine, or it could be far less. There is a variable here we do not know. In fact, if this engine made less torque than the 6000 RPm engine, you proably would find the DC of the same size injector at 9000 RPm to make 500 Hp will be lower, therefore allowing a smaller Injector to be used. All other factors remaining the same. Same MAP, same fuel pressure etc.
Typically to achieve 500 HP at any RPM requires a certain amount of air volume. You can figure out the air volume of an engine based upon the AF number you are running. Pretty simple math excercise. The VE of an engine can be then calculated. From memory VE is the theoretical air mass number divided by the actual air mass number multipled by 100%. If you log the VE of an engine and typically it goes down with RPM, why would you need more fuel? Practical dyno testing shows this to be true.
What I have always understood in sizing Injectors is the expected HP of the engine is divided by the BSFC number to be used, divided by the number of Cylinders multiplied by the Injector Duty Cycle you wish to run.
HP/ required BSFC / number of Cylinders x Injector DC. There are some minor variations of this, but in essence most calculations are done this way.
If we wanted 500 BHP and a BSFC number of 0.6 and 4 Cylinders and run the Injectors at 85 % DC, leaving 15 % until the Injectors are wide open, the calculation would be this
500BHP /0.6 BSFC /4 Cylinders x 1.15DC = 86.25 Lbs per Hour fuel required per Injector. We would then find an Injector rated at this flow rate at the desired Fuel pressure we wish to run. Uping the Fuel Pressure changes this number some. I think from memory the % change here is the square root of the new pressure divided by the old pressure. I may have this backwards. I'm no expert here.
I see no where in any accepted calculation where RPM is a variable in Injector sizing.
Patrick, don't take my word here. For sure do not take any view expressed here by me or anyone else for that matter as been expert advice. If we were experts, we would not be posting here. We would have no reason to. Your engine is far more valuable to put to risk by accepting my advice or that of A Wayne. Neither of us make our living doing this stuff. Ask those who do. I know you are in contact with someone who does this stuff and has been doing this for a very long time with success. His advice you should seek and to be sure get a second opinion from another expert. Neither of which I or A Wayne are!!
To go back to the original comment that drew my attention, why does an Injector need to be bigger for 500HP at 9000 RPM than it needs to be for 500HP at 6000 RPM? Injector sizing is based upon the air volume the engine injests, per stroke, not its RPM. The reason the fuel demand goes down at higher speeds is the valve event time is less. Less time for the Intake valve to be open requires less fuel to maintain the same AF number. The biggest fuel demand is at peak torque where the engine is most efficient. This is why when logging the AF trace, there is always a dip at peak torque. Look at the Injection pulse times at the higher speeds. They will always be less that at peak torque.
500 HP at 6000 RPM will require the same Injector size as 500 HP at 9000 RPM. Given these are peak HP numbers. If we make some assumptions here based upon what the poster stated, we could say the 6000 RPM engine must make somewhere close to 500 units of Torque, unless the VE of this engine just drops thro the floor in 800 RPM. On the other hand we cannot make this same assumption on the 9000 RPm engine. The torque curve could be very broad and the peak torque could be close to 500 units as in the case of the 6000 RPM engine, or it could be far less. There is a variable here we do not know. In fact, if this engine made less torque than the 6000 RPm engine, you proably would find the DC of the same size injector at 9000 RPm to make 500 Hp will be lower, therefore allowing a smaller Injector to be used. All other factors remaining the same. Same MAP, same fuel pressure etc.
Typically to achieve 500 HP at any RPM requires a certain amount of air volume. You can figure out the air volume of an engine based upon the AF number you are running. Pretty simple math excercise. The VE of an engine can be then calculated. From memory VE is the theoretical air mass number divided by the actual air mass number multipled by 100%. If you log the VE of an engine and typically it goes down with RPM, why would you need more fuel? Practical dyno testing shows this to be true.
What I have always understood in sizing Injectors is the expected HP of the engine is divided by the BSFC number to be used, divided by the number of Cylinders multiplied by the Injector Duty Cycle you wish to run.
HP/ required BSFC / number of Cylinders x Injector DC. There are some minor variations of this, but in essence most calculations are done this way.
If we wanted 500 BHP and a BSFC number of 0.6 and 4 Cylinders and run the Injectors at 85 % DC, leaving 15 % until the Injectors are wide open, the calculation would be this
500BHP /0.6 BSFC /4 Cylinders x 1.15DC = 86.25 Lbs per Hour fuel required per Injector. We would then find an Injector rated at this flow rate at the desired Fuel pressure we wish to run. Uping the Fuel Pressure changes this number some. I think from memory the % change here is the square root of the new pressure divided by the old pressure. I may have this backwards. I'm no expert here.
I see no where in any accepted calculation where RPM is a variable in Injector sizing.
Patrick, don't take my word here. For sure do not take any view expressed here by me or anyone else for that matter as been expert advice. If we were experts, we would not be posting here. We would have no reason to. Your engine is far more valuable to put to risk by accepting my advice or that of A Wayne. Neither of us make our living doing this stuff. Ask those who do. I know you are in contact with someone who does this stuff and has been doing this for a very long time with success. His advice you should seek and to be sure get a second opinion from another expert. Neither of which I or A Wayne are!!
02-10-2008, 06:19 PM
#82
Rennlist Member
Thread Starter
Well like many threads, this one just moves about naturally so no harm posting thoughts and opinions. This won't alter what actually goes in the car as it is being handled by the experts as you mention. I have learned a few things here however so don't stop posting. Some of what goes into these threads gives my rise to ask certain questions of the experts and the learning process continues.
thanks
I might ask if anyone uses the LINK gauge display or can recommend others?
thanks
I might ask if anyone uses the LINK gauge display or can recommend others?
02-10-2008, 08:25 PM
#83
Formula One Spin Doctor
Rennlist Member
Rennlist Member
Ok, I'm back. Sorry about that. I had a short trip to take. Also, my spelling is poor, or should I say, my keyboard control.
To go back to the original comment that drew my attention, why does an Injector need to be bigger for 500HP at 9000 RPM than it needs to be for 500HP at 6000 RPM? Injector sizing is based upon the air volume the engine injests, per stroke, not its RPM. The reason the fuel demand goes down at higher speeds is the valve event time is less. Less time for the Intake valve to be open requires less fuel to maintain the same AF number. The biggest fuel demand is at peak torque where the engine is most efficient. This is why when logging the AF trace, there is always a dip at peak torque. Look at the Injection pulse times at the higher speeds. They will always be less that at peak torque.
500 HP at 6000 RPM will require the same Injector size as 500 HP at 9000 RPM. Given these are peak HP numbers. If we make some assumptions here based upon what the poster stated, we could say the 6000 RPM engine must make somewhere close to 500 units of Torque, unless the VE of this engine just drops thro the floor in 800 RPM. On the other hand we cannot make this same assumption on the 9000 RPm engine. The torque curve could be very broad and the peak torque could be close to 500 units as in the case of the 6000 RPM engine, or it could be far less. There is a variable here we do not know. In fact, if this engine made less torque than the 6000 RPm engine, you proably would find the DC of the same size injector at 9000 RPm to make 500 Hp will be lower, therefore allowing a smaller Injector to be used. All other factors remaining the same. Same MAP, same fuel pressure etc.
Typically to achieve 500 HP at any RPM requires a certain amount of air volume. You can figure out the air volume of an engine based upon the AF number you are running. Pretty simple math excercise. The VE of an engine can be then calculated. From memory VE is the theoretical air mass number divided by the actual air mass number multipled by 100%. If you log the VE of an engine and typically it goes down with RPM, why would you need more fuel? Practical dyno testing shows this to be true.
What I have always understood in sizing Injectors is the expected HP of the engine is divided by the BSFC number to be used, divided by the number of Cylinders multiplied by the Injector Duty Cycle you wish to run.
HP/ required BSFC / number of Cylinders x Injector DC. There are some minor variations of this, but in essence most calculations are done this way.
If we wanted 500 BHP and a BSFC number of 0.6 and 4 Cylinders and run the Injectors at 85 % DC, leaving 15 % until the Injectors are wide open, the calculation would be this
500BHP /0.6 BSFC /4 Cylinders x 1.15DC = 86.25 Lbs per Hour fuel required per Injector. We would then find an Injector rated at this flow rate at the desired Fuel pressure we wish to run. Uping the Fuel Pressure changes this number some. I think from memory the % change here is the square root of the new pressure divided by the old pressure. I may have this backwards. I'm no expert here.
I see no where in any accepted calculation where RPM is a variable in Injector sizing.
Patrick, don't take my word here. For sure do not take any view expressed here by me or anyone else for that matter as been expert advice. If we were experts, we would not be posting here. We would have no reason to. Your engine is far more valuable to put to risk by accepting my advice or that of A Wayne. Neither of us make our living doing this stuff. Ask those who do. I know you are in contact with someone who does this stuff and has been doing this for a very long time with success. His advice you should seek and to be sure get a second opinion from another expert. Neither of which I or A Wayne are!!
To go back to the original comment that drew my attention, why does an Injector need to be bigger for 500HP at 9000 RPM than it needs to be for 500HP at 6000 RPM? Injector sizing is based upon the air volume the engine injests, per stroke, not its RPM. The reason the fuel demand goes down at higher speeds is the valve event time is less. Less time for the Intake valve to be open requires less fuel to maintain the same AF number. The biggest fuel demand is at peak torque where the engine is most efficient. This is why when logging the AF trace, there is always a dip at peak torque. Look at the Injection pulse times at the higher speeds. They will always be less that at peak torque.
500 HP at 6000 RPM will require the same Injector size as 500 HP at 9000 RPM. Given these are peak HP numbers. If we make some assumptions here based upon what the poster stated, we could say the 6000 RPM engine must make somewhere close to 500 units of Torque, unless the VE of this engine just drops thro the floor in 800 RPM. On the other hand we cannot make this same assumption on the 9000 RPm engine. The torque curve could be very broad and the peak torque could be close to 500 units as in the case of the 6000 RPM engine, or it could be far less. There is a variable here we do not know. In fact, if this engine made less torque than the 6000 RPm engine, you proably would find the DC of the same size injector at 9000 RPm to make 500 Hp will be lower, therefore allowing a smaller Injector to be used. All other factors remaining the same. Same MAP, same fuel pressure etc.
Typically to achieve 500 HP at any RPM requires a certain amount of air volume. You can figure out the air volume of an engine based upon the AF number you are running. Pretty simple math excercise. The VE of an engine can be then calculated. From memory VE is the theoretical air mass number divided by the actual air mass number multipled by 100%. If you log the VE of an engine and typically it goes down with RPM, why would you need more fuel? Practical dyno testing shows this to be true.
What I have always understood in sizing Injectors is the expected HP of the engine is divided by the BSFC number to be used, divided by the number of Cylinders multiplied by the Injector Duty Cycle you wish to run.
HP/ required BSFC / number of Cylinders x Injector DC. There are some minor variations of this, but in essence most calculations are done this way.
If we wanted 500 BHP and a BSFC number of 0.6 and 4 Cylinders and run the Injectors at 85 % DC, leaving 15 % until the Injectors are wide open, the calculation would be this
500BHP /0.6 BSFC /4 Cylinders x 1.15DC = 86.25 Lbs per Hour fuel required per Injector. We would then find an Injector rated at this flow rate at the desired Fuel pressure we wish to run. Uping the Fuel Pressure changes this number some. I think from memory the % change here is the square root of the new pressure divided by the old pressure. I may have this backwards. I'm no expert here.
I see no where in any accepted calculation where RPM is a variable in Injector sizing.
Patrick, don't take my word here. For sure do not take any view expressed here by me or anyone else for that matter as been expert advice. If we were experts, we would not be posting here. We would have no reason to. Your engine is far more valuable to put to risk by accepting my advice or that of A Wayne. Neither of us make our living doing this stuff. Ask those who do. I know you are in contact with someone who does this stuff and has been doing this for a very long time with success. His advice you should seek and to be sure get a second opinion from another expert. Neither of which I or A Wayne are!!
Pleaseee!
You should be very careful with your conjecture and lack of understanding on the subject matter, i do not profess to be an "expert" but i do have an understanding of where to go with this, we can agree to dis-agree as anyone else here can, i can respect that , Fine, but lay your assumptions at your feet not mine.
You in turn should consult your expert , have him explain the missing links and not make such ridiculous assumptions , with static formulas. Please show him the dyno sheet previously posted , Now where would your injection time and duty cycle be at it's highest and where after the TQ peak would you start make your adjustment to reduce the fuel , as you claim. Please post your's or your experts answer, it would be interesting to see,the answer to the actual question , instead of this tap dance....
333 pg 333.
There are a lot of options for what you are looking for , i would look carefully at what is available , find someone in the power range and usage of what you are doing , then make a decision on your system and accompanying dashboard . choosing wrong here on your management and tuner could turn your project into a disaster.
Last edited by A.Wayne; 02-10-2008 at 09:23 PM.
02-10-2008, 09:45 PM
#84
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Its fairly simple…..really!
For correct mixtures you need to inject the correct volume of fuel for each firing event. As RPM goes up the time available for fuel injection goes down (nothing to do with efficiency – its just a physical fact. If the engine is spinning twice as fast you have half as long for the max injector time). So the increase in duty cycle as the RPMs go up is not the need for more fuel per firing event, it is the decrease in time available. As the RPMs increase you will eventually run out of duty cycle if the injector is not large enough. By increasing the capacity of the injector you will decrease the time it takes to deliver the same amount of fuel - thereby reducing the duty cycle at the same load / RPM.
The problem on the other end of the scale (idle) is the minimum injector turn on time. Fuel injectors are a physical device – due to the inertia of the moving parts there is a minimum signal length that will actually open the injector (this is where the low impedance peak and hold injector can usually respond better).
BTW – the adjustment for VE, BSFC and such is fairly small for our engines – they have a wide efficiency bandwidth.
For correct mixtures you need to inject the correct volume of fuel for each firing event. As RPM goes up the time available for fuel injection goes down (nothing to do with efficiency – its just a physical fact. If the engine is spinning twice as fast you have half as long for the max injector time). So the increase in duty cycle as the RPMs go up is not the need for more fuel per firing event, it is the decrease in time available. As the RPMs increase you will eventually run out of duty cycle if the injector is not large enough. By increasing the capacity of the injector you will decrease the time it takes to deliver the same amount of fuel - thereby reducing the duty cycle at the same load / RPM.
The problem on the other end of the scale (idle) is the minimum injector turn on time. Fuel injectors are a physical device – due to the inertia of the moving parts there is a minimum signal length that will actually open the injector (this is where the low impedance peak and hold injector can usually respond better).
BTW – the adjustment for VE, BSFC and such is fairly small for our engines – they have a wide efficiency bandwidth.
02-10-2008, 10:09 PM
#85
A Wayne,
No tap dance here. No personel attacks either. I much prefer to pass again. Any discussion with you included, consider me out.
You sir are far from been anywhere close to the level of "my" expert. Never think you are even in the same game.
No tap dance here. No personel attacks either. I much prefer to pass again. Any discussion with you included, consider me out.
You sir are far from been anywhere close to the level of "my" expert. Never think you are even in the same game.
02-10-2008, 10:15 PM
#86
One final question Mr Wayne,
Do you still stand behind this statement?
"""Eniac
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 """
Do you still stand behind this statement?
"""Eniac
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 """
02-10-2008, 11:15 PM
#87
Formula One Spin Doctor
Rennlist Member
Rennlist Member
Before you run off could you answer my question or can we attend to the multiple holes in your above theories, Alas it appears you have chosen the safe way out and exit via the back door, you know me being a bad guy and everything.
In the future I'm asking you not to speak for me, as you did in your previous post about knowing and not knowing as you don't know me and i'm still waiting for the results from your last absurd comments about making gobs of HP from CDI systems, to know you.
My suggestion is use your "expert" more often and have him explain in terms you can understand , nothing Personal and nothing against your expert , whomever he or she maybe, I'm sure there is a wealth of knowledge from such person, but don't try to use that to profess you are in the know. I enjoy the banter when there is exchange and never professed to be an expert, just happen to live at an Holiday inn express.... cheers
PS, Me thinks chris made an attempt to explain it again !
Last edited by A.Wayne; 02-10-2008 at 11:41 PM.
02-10-2008, 11:48 PM
#88
Ok, I will give this one last shot, or ask you to.
As you mention the CDI discussion, you bring up a very interesting point, one that others have asked you also.
You sir NEVER EVER supply any data or theorems when asked. You sir NEVER back up any of your statements with facts or mathmatical data to prove your point. You did the same with the CDI discussion and you have done the same here.
I sir have done this in both discussions and have been shot down by you in both discussions without you even offering anything like a simple calculation or equation to back anything you have to say, other than some dyno sheet that does not even suggest been the same as your original statement. It is for this reason I am not prepared to continue with anything with you as it is pointless unless you can offer something other than your short nasty jabs. It has been asked of you before by others, but you continue to hide in the shadows and pretend to offer something. I sir am happy to continue, but with someone who can offer up some emperical data specific to the subject in discussion. I am not afraid of been wrong. I am wrong many times a day. At least my wife tells this to me. I am not afriad of learning something either.
As you mention the CDI discussion, you bring up a very interesting point, one that others have asked you also.
You sir NEVER EVER supply any data or theorems when asked. You sir NEVER back up any of your statements with facts or mathmatical data to prove your point. You did the same with the CDI discussion and you have done the same here.
I sir have done this in both discussions and have been shot down by you in both discussions without you even offering anything like a simple calculation or equation to back anything you have to say, other than some dyno sheet that does not even suggest been the same as your original statement. It is for this reason I am not prepared to continue with anything with you as it is pointless unless you can offer something other than your short nasty jabs. It has been asked of you before by others, but you continue to hide in the shadows and pretend to offer something. I sir am happy to continue, but with someone who can offer up some emperical data specific to the subject in discussion. I am not afraid of been wrong. I am wrong many times a day. At least my wife tells this to me. I am not afriad of learning something either.
02-10-2008, 11:54 PM
#89
Formula One Spin Doctor
Rennlist Member
Rennlist Member
Ok, I'm back. Sorry about that. I had a short trip to take. Also, my spelling is poor, or should I say, my keyboard control.
To go back to the original comment that drew my attention, why does an Injector need to be bigger for 500HP at 9000 RPM than it needs to be for 500HP at 6000 RPM? Injector sizing is based upon the air volume the engine injests, per stroke, not its RPM. The reason the fuel demand goes down at higher speeds is the valve event time is less. Less time for the Intake valve to be open requires less fuel to maintain the same AF number. The biggest fuel demand is at peak torque where the engine is most fficient. This is why when logging the AF trace, there is always a dip at peak torque. Look at the Injection pulse times at the higher speeds. They will always be less that at peak torque.
500 HP at 6000 RPM will require the same Injector size as 500 HP at 9000 RPM. Given these are peak HP numbers. If we make some assumptions here based upon what the poster stated, we could say the 6000 RPM engine must make somewhere close to 500 units of Torque, unless the VE of this engine just drops thro the floor in 800 RPM. On the other hand we cannot make this same assumption on the 9000 RPm engine. The torque curve could be very broad and the peak torque could be close to 500 units as in the case of the 6000 RPM engine, or it could be far less. There is a variable here we do not know. In fact, if this engine made less torque than the 6000 RPm engine, you proably would find the DC of the same size injector at 9000 RPm to make 500 Hp will be lower, therefore allowing a smaller Injector to be used. All other factors remaining the same. Same MAP, same fuel pressure etc.
Typically to achieve 500 HP at any RPM requires a certain amount of air volume. You can figure out the air volume of an engine based upon the AF number you are running. Pretty simple math excercise. The VE of an engine can be then calculated. From memory VE is the theoretical air mass number divided by the actual air mass number multipled by 100%. If you log the VE of an engine and typically it goes down with RPM, why would you need more fuel? Practical dyno testing shows this to be true.
What I have always understood in sizing Injectors is the expected HP of the engine is divided by the BSFC number to be used, divided by the number of Cylinders multiplied by the Injector Duty Cycle you wish to run.
HP/ required BSFC / number of Cylinders x Injector DC. There are some minor variations of this, but in essence most calculations are done this way.
If we wanted 500 BHP and a BSFC number of 0.6 and 4 Cylinders and run the Injectors at 85 % DC, leaving 15 % until the Injectors are wide open, the calculation would be this
500BHP /0.6 BSFC /4 Cylinders x 1.15DC = 86.25 Lbs per Hour fuel required per Injector. We would then find an Injector rated at this flow rate at the desired Fuel pressure we wish to run. Uping the Fuel Pressure changes this number some. I think from memory the % change here is the square root of the new pressure divided by the old pressure. I may have this backwards. I'm no expert here.
I see no where in any accepted calculation where RPM is a variable in Injector sizing.
Patrick, don't take my word here. For sure do not take any view expressed here by me or anyone else for that matter as been expert advice. If we were experts, we would not be posting here. We would have no reason to. Your engine is far more valuable to put to risk by accepting my advice or that of A Wayne. Neither of us make our living doing this stuff. Ask those who do. I know you are in contact with someone who does this stuff and has been doing this for a very long time with success. His advice you should seek and to be sure get a second opinion from another expert. Neither of which I or A Wayne are!!
To go back to the original comment that drew my attention, why does an Injector need to be bigger for 500HP at 9000 RPM than it needs to be for 500HP at 6000 RPM? Injector sizing is based upon the air volume the engine injests, per stroke, not its RPM. The reason the fuel demand goes down at higher speeds is the valve event time is less. Less time for the Intake valve to be open requires less fuel to maintain the same AF number. The biggest fuel demand is at peak torque where the engine is most fficient. This is why when logging the AF trace, there is always a dip at peak torque. Look at the Injection pulse times at the higher speeds. They will always be less that at peak torque.
500 HP at 6000 RPM will require the same Injector size as 500 HP at 9000 RPM. Given these are peak HP numbers. If we make some assumptions here based upon what the poster stated, we could say the 6000 RPM engine must make somewhere close to 500 units of Torque, unless the VE of this engine just drops thro the floor in 800 RPM. On the other hand we cannot make this same assumption on the 9000 RPm engine. The torque curve could be very broad and the peak torque could be close to 500 units as in the case of the 6000 RPM engine, or it could be far less. There is a variable here we do not know. In fact, if this engine made less torque than the 6000 RPm engine, you proably would find the DC of the same size injector at 9000 RPm to make 500 Hp will be lower, therefore allowing a smaller Injector to be used. All other factors remaining the same. Same MAP, same fuel pressure etc.
Typically to achieve 500 HP at any RPM requires a certain amount of air volume. You can figure out the air volume of an engine based upon the AF number you are running. Pretty simple math excercise. The VE of an engine can be then calculated. From memory VE is the theoretical air mass number divided by the actual air mass number multipled by 100%. If you log the VE of an engine and typically it goes down with RPM, why would you need more fuel? Practical dyno testing shows this to be true.
What I have always understood in sizing Injectors is the expected HP of the engine is divided by the BSFC number to be used, divided by the number of Cylinders multiplied by the Injector Duty Cycle you wish to run.
HP/ required BSFC / number of Cylinders x Injector DC. There are some minor variations of this, but in essence most calculations are done this way.
If we wanted 500 BHP and a BSFC number of 0.6 and 4 Cylinders and run the Injectors at 85 % DC, leaving 15 % until the Injectors are wide open, the calculation would be this
500BHP /0.6 BSFC /4 Cylinders x 1.15DC = 86.25 Lbs per Hour fuel required per Injector. We would then find an Injector rated at this flow rate at the desired Fuel pressure we wish to run. Uping the Fuel Pressure changes this number some. I think from memory the % change here is the square root of the new pressure divided by the old pressure. I may have this backwards. I'm no expert here.
I see no where in any accepted calculation where RPM is a variable in Injector sizing.
Patrick, don't take my word here. For sure do not take any view expressed here by me or anyone else for that matter as been expert advice. If we were experts, we would not be posting here. We would have no reason to. Your engine is far more valuable to put to risk by accepting my advice or that of A Wayne. Neither of us make our living doing this stuff. Ask those who do. I know you are in contact with someone who does this stuff and has been doing this for a very long time with success. His advice you should seek and to be sure get a second opinion from another expert. Neither of which I or A Wayne are!!
Ok, I will give this one last shot, or ask you to.
As you mention the CDI discussion, you bring up a very interesting point, one that others have asked you also.
You sir NEVER EVER supply any data or theorems when asked. You sir NEVER back up any of your statements with facts or mathmatical data to prove your point. You did the same with the CDI discussion and you have done the same here.
I sir have done this in both discussions and have been shot down by you in both discussions without you even offering anything like a simple calculation or equation to back anything you have to say, other than some dyno sheet that does not even suggest been the same as your original statement. It is for this reason I am not prepared to continue with anything with you as it is pointless unless you can offer something other than your short nasty jabs. It has been asked of you before by others, but you continue to hide in the shadows and pretend to offer something. I sir am happy to continue, but with someone who can offer up some emperical data specific to the subject in discussion. I am not afraid of been wrong. I am wrong many times a day. At least my wife tells this to me. I am not afriad of learning something either.
As you mention the CDI discussion, you bring up a very interesting point, one that others have asked you also.
You sir NEVER EVER supply any data or theorems when asked. You sir NEVER back up any of your statements with facts or mathmatical data to prove your point. You did the same with the CDI discussion and you have done the same here.
I sir have done this in both discussions and have been shot down by you in both discussions without you even offering anything like a simple calculation or equation to back anything you have to say, other than some dyno sheet that does not even suggest been the same as your original statement. It is for this reason I am not prepared to continue with anything with you as it is pointless unless you can offer something other than your short nasty jabs. It has been asked of you before by others, but you continue to hide in the shadows and pretend to offer something. I sir am happy to continue, but with someone who can offer up some emperical data specific to the subject in discussion. I am not afraid of been wrong. I am wrong many times a day. At least my wife tells this to me. I am not afriad of learning something either.
You are married, Shhhhish, the generosity of women never fails to amaze me.
Apart from that you are plain nuts, Nuts i say , you are either a Python or a lawyer ( fick, that 's the same ) Ok a nutty buddy or Fred Astaire , Yes Fred , I reconize the tap dancing .....
Start spreading the news ,,,,,, daah laa, dah dhum , Turn ,
02-11-2008, 12:09 AM
#90
I ask one more time in the hope you will offer up some real data.
Prove with mathmatical data and any dyno logs of Injector times showing that an engine making 500HP at 9000 RPM would require bigger Injectors than an engine making 500HP at 6000 RPM, given all other factors been the same. Or that at 9000 RPM the FP could not be increased where the Injector DC would be at 100% and require larger Injectors to make 500 HP. This is what I understand you stated. No more jabs.
Lets make it simple here. Lets consider the engine been a 4 Cylinder and it will run at a constant MAP and at a AF of 12.5: 1.0. @ 72 PSI FP. From simple math we should agree that this engine will allow 20 msec of injection time at 6000 RPM and 13 msecs at 9000 RPM. Thats 125 HP per Cylinder. Now show me with mathmatical calculations that an Injector calculated with my formula cannot supply enough fuel to make 125HP per Cylinder in 13 msecs.
Prove with mathmatical data and any dyno logs of Injector times showing that an engine making 500HP at 9000 RPM would require bigger Injectors than an engine making 500HP at 6000 RPM, given all other factors been the same. Or that at 9000 RPM the FP could not be increased where the Injector DC would be at 100% and require larger Injectors to make 500 HP. This is what I understand you stated. No more jabs.
Lets make it simple here. Lets consider the engine been a 4 Cylinder and it will run at a constant MAP and at a AF of 12.5: 1.0. @ 72 PSI FP. From simple math we should agree that this engine will allow 20 msec of injection time at 6000 RPM and 13 msecs at 9000 RPM. Thats 125 HP per Cylinder. Now show me with mathmatical calculations that an Injector calculated with my formula cannot supply enough fuel to make 125HP per Cylinder in 13 msecs.