Engine guru's/ fuel injectors
03-14-2008, 11:51 PM
#21
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Thread Starter
I spoke with AZ Speed and Marine this evening and they suggested a 63lb nozzle wirh a static 53psi base line and reflash the ECM accordingly. They did my setup the last time. 4 years and 200 hours with pretty much no problems.
03-15-2008, 01:26 AM
#22
Charter Member #601
Charter Member
One thing that has to be considered.. the more PSI you put to an injector the harder it is to open it. More current to open it. Causing heat. If they get too hot they can start to stick and self destruct. Also you have to know what type of driver is in the ECU and not over work it or it will die also.
Most are rated at 43.5 psi. You go up from there to get a bit more flow. But going to the next step is recommended. So you dont have to run such hi psi.
Go to Marren injection and see what they say about psi and current draw. From about 50 lbs/hr on up, they are all low Z. There are some out there that are higher and still are high Z. Low Z injectors take a lot of current. When you bump up the psi.. the current draw goes up on the driver.
AZ's recommendation is probably in the ball park.
Here is a site to play with psi.. but not the bsfc. They call it .5 for NA.. where in a blown setup, it will be more like .6-.7
http://www.rbracing-rsr.com/fuelinjectors.htm
Another site... http://www.injector.com/injectorselection.php
you can vary the bsfc on this one. Play with it..
Hope this helps.
Dick
Most are rated at 43.5 psi. You go up from there to get a bit more flow. But going to the next step is recommended. So you dont have to run such hi psi.
Go to Marren injection and see what they say about psi and current draw. From about 50 lbs/hr on up, they are all low Z. There are some out there that are higher and still are high Z. Low Z injectors take a lot of current. When you bump up the psi.. the current draw goes up on the driver.
AZ's recommendation is probably in the ball park.
Here is a site to play with psi.. but not the bsfc. They call it .5 for NA.. where in a blown setup, it will be more like .6-.7
http://www.rbracing-rsr.com/fuelinjectors.htm
Another site... http://www.injector.com/injectorselection.php
you can vary the bsfc on this one. Play with it..
Hope this helps.
Dick
Last edited by Mr Gadgets; 03-15-2008 at 01:45 AM.
03-15-2008, 01:44 AM
#23
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If you use marrens fuel injection guide: scroll down to the second calculator
http://www.injector.com/injectorselection.php
You can play with the numbers and get a feel for what they will handle. Something everyone needs to remember is in a "ideal" application you would have a injector that is appropiately sized to the hp limit of your motor using 43.5 base pressure and a 1-1 boost referencing regulator. The problem guys like R beyer and myself have though is we are still using factory mefi ecm's and they will only run high impedance injectors. The biggest high impedance injector out there is the siemens 63 lb (also often rated at 60 lbs).
So in order to make 800 hp the fuel pressure needs to be raised MUCH more than 1 lb for every lb of boost. As said in earlier post,by doing this your are effectively making a medium size or fairly small injector act like a much bigger one until you reach the point it quits working completely.When calculating a supercharged motor you will want to enter at least a .55 bsfc if not a .6 bsfc for your calculations.
For example: a 50 lb injector will only support 581 hp at 43.5 psi and a bsfc of .55. Now lets say your running a blower and you plan on making 850 hp (at .55 bsfc),if you keep the pressure at a steady 43.5 you would need 73 lb injectors.Again,the only injectors over 60/63 lb are low impedance which require a aftermarket ecu and program which is great for the guy with a unlimited budget or tuning time on the dyno or water but what do you do if your sticking with a oem ecu or a cheap aftermarket one that will only run high impedance injectors? The answer is you raise fuel pressure. Now all of my hp support calculations are assuming your programming has the injectors maxed out at 80% duty cycle based on a bsfc of .55 for a blown motor,if you were going to hold it at WOT for a extended time you would possibly want to plan for a bsfc of .6 which will typically get you somewhere into the 11-1 afr.
Back to raising the fuel pressure,that same 50 lb injector that only supported 581 hp at 43.5 psi now flows 67.8 lbs
(change the injector size to 50 lbs ,the max pressure to 80 lbs then hit calc)
http://www.csgnetwork.com/fiflowcalc.html
Going back to the Marren calculator (make sure you scroll down to the second calculastor),that injector will now support 788 hp at .55 bsfc,867 hp at .50 bsfc and 723 hp at .6 bsfc.
Alot of guys will tell you that injectors will "shut down" at 80 psi,these modern siemens injectors don't seem to really have that problem,I am making over 1000 hp with the 60/63lb versions at about 80-85 psi in my blown application. I hope the links help give you guys some insight plus you can play with the numbers and see where you land at,Smitty
http://www.injector.com/injectorselection.php
You can play with the numbers and get a feel for what they will handle. Something everyone needs to remember is in a "ideal" application you would have a injector that is appropiately sized to the hp limit of your motor using 43.5 base pressure and a 1-1 boost referencing regulator. The problem guys like R beyer and myself have though is we are still using factory mefi ecm's and they will only run high impedance injectors. The biggest high impedance injector out there is the siemens 63 lb (also often rated at 60 lbs).
So in order to make 800 hp the fuel pressure needs to be raised MUCH more than 1 lb for every lb of boost. As said in earlier post,by doing this your are effectively making a medium size or fairly small injector act like a much bigger one until you reach the point it quits working completely.When calculating a supercharged motor you will want to enter at least a .55 bsfc if not a .6 bsfc for your calculations.
For example: a 50 lb injector will only support 581 hp at 43.5 psi and a bsfc of .55. Now lets say your running a blower and you plan on making 850 hp (at .55 bsfc),if you keep the pressure at a steady 43.5 you would need 73 lb injectors.Again,the only injectors over 60/63 lb are low impedance which require a aftermarket ecu and program which is great for the guy with a unlimited budget or tuning time on the dyno or water but what do you do if your sticking with a oem ecu or a cheap aftermarket one that will only run high impedance injectors? The answer is you raise fuel pressure. Now all of my hp support calculations are assuming your programming has the injectors maxed out at 80% duty cycle based on a bsfc of .55 for a blown motor,if you were going to hold it at WOT for a extended time you would possibly want to plan for a bsfc of .6 which will typically get you somewhere into the 11-1 afr.
Back to raising the fuel pressure,that same 50 lb injector that only supported 581 hp at 43.5 psi now flows 67.8 lbs
(change the injector size to 50 lbs ,the max pressure to 80 lbs then hit calc)
http://www.csgnetwork.com/fiflowcalc.html
Going back to the Marren calculator (make sure you scroll down to the second calculastor),that injector will now support 788 hp at .55 bsfc,867 hp at .50 bsfc and 723 hp at .6 bsfc.
Alot of guys will tell you that injectors will "shut down" at 80 psi,these modern siemens injectors don't seem to really have that problem,I am making over 1000 hp with the 60/63lb versions at about 80-85 psi in my blown application. I hope the links help give you guys some insight plus you can play with the numbers and see where you land at,Smitty
Last edited by articfriends; 03-15-2008 at 01:46 AM.
03-15-2008, 01:51 AM
#24
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iTrader: (1)
So back to your question,will your 50 lb injectors support 800 hp,it will be VERY marginal as they will only support 788 hp at .55 bsfc. I would buy the next size bigger and have a little safety margin,Smitty
03-15-2008, 01:52 AM
#25
Platinum Member
Platinum Member
iTrader: (1)
One thing that has to be considered.. the more PSI you put to an injector the harder it is to open it. More current to open it. Causing heat. If they get too hot they can start to stick and self destruct. Also you have to know what type of driver is in the ECU and not over work it or it will die also.
Most are rated at 43.5 psi. You go up from there to get a bit more flow. But going to the next step is recommended. So you dont have to run such hi psi.
Go to Marren injection and see what they say about psi and current draw. From about 50 lbs/hr on up, they are all low Z. There are some out there that are higher and still are high Z. Low Z injectors take a lot of current. When you bump up the psi.. the current draw goes up on the driver.
AZ's recommendation is probably in the ball park.
Here is a site to play with psi.. but not the bsfc. They call it .5 for NA.. where in a blown setup, it will be more like .6-.7
http://www.rbracing-rsr.com/fuelinjectors.htm
Another site... http://www.injector.com/injectorselection.php
you can vary the bsfc on this one. Play with it..
Hope this helps.
Dick
Most are rated at 43.5 psi. You go up from there to get a bit more flow. But going to the next step is recommended. So you dont have to run such hi psi.
Go to Marren injection and see what they say about psi and current draw. From about 50 lbs/hr on up, they are all low Z. There are some out there that are higher and still are high Z. Low Z injectors take a lot of current. When you bump up the psi.. the current draw goes up on the driver.
AZ's recommendation is probably in the ball park.
Here is a site to play with psi.. but not the bsfc. They call it .5 for NA.. where in a blown setup, it will be more like .6-.7
http://www.rbracing-rsr.com/fuelinjectors.htm
Another site... http://www.injector.com/injectorselection.php
you can vary the bsfc on this one. Play with it..
Hope this helps.
Dick
,Smitty
03-15-2008, 11:50 AM
#28
Platinum Member
Platinum Member
iTrader: (1)
There is no doubt that running a fuel system basically maxed out at 80 psi is hard on the fuel pump and definately draws ALOT of current. I have been running my system this way for 7 years,I have never had a fuel pump failure BUT I have had 3 different fuel pumps,the original red aeromotive that I ran for 3 years which is now on a hopped up N/A 540 in a friends boat (it couldn't keep up with my demand when I went from a 502 to a 540. Then I bought a billet essex pump which had a better lbs per hr rating at the higher pressure,I ran this for several years on my 540 but again when I bumped up the hp it couldn't put out enough to keep up. My current pump,a aeromotive elimnator has been on my boat for 3 seasons along with a voltage booster that makes it put out even more lbs per hr at high pressure under boost,problem free so far. I imagine if I ran this current fuel pump in this configuration enough hours (probably around the 250 hr mark) it would eventually fail. I carry the essex pump with me as a spare in case I'm ever stranded or break down when on vacation out of town. I know I could have bought a weldon 2025 or 2035 like what gpm is running BUT the flow output is too great under light cruising loads for my regulators and fuel lines to handle,Smitty
Last edited by articfriends; 03-15-2008 at 11:53 AM.
03-15-2008, 01:11 PM
#29
Charter Member #601
Charter Member
I just posted this message and see you guys have been discussing it.
Another thought on this subject is if you do need to run extreme psi to make you goal, then you need a fuel system that can cope with that much psi and flow. Smitty, are you using a box to increase your voltage to fuel pump to gain that high psi? And current draw on the fuel system could effect available voltage to the ECU. I found that to be the case in one situation.. Pulse Width Modulation driver circuits for low Z injectors noised up the 12v for the ECU. I installed a circuit that is a Peak and Hold driver circuit.
An option to consider is a low Z driver box. Not sure if the Merc ECU would be compatible with such a box. If it was, then your options open up a bit more. Do you spend money to make the fuel psi.. or buy bigger injectors and maybe a driver box?
I am going to try a mechanical pump this time around to lessen the load on the electrical system. It is cheaper than buying a new pump and controller box. I will be running 96lbs injectors and figure I will need about 55psi at max boost.
I agree with Smitty.. you probably ought to make a jump to the next size. And compare prices with low Z and high Z and what it might take to setup the system.
Dick
Another thought on this subject is if you do need to run extreme psi to make you goal, then you need a fuel system that can cope with that much psi and flow. Smitty, are you using a box to increase your voltage to fuel pump to gain that high psi? And current draw on the fuel system could effect available voltage to the ECU. I found that to be the case in one situation.. Pulse Width Modulation driver circuits for low Z injectors noised up the 12v for the ECU. I installed a circuit that is a Peak and Hold driver circuit.
An option to consider is a low Z driver box. Not sure if the Merc ECU would be compatible with such a box. If it was, then your options open up a bit more. Do you spend money to make the fuel psi.. or buy bigger injectors and maybe a driver box?
I am going to try a mechanical pump this time around to lessen the load on the electrical system. It is cheaper than buying a new pump and controller box. I will be running 96lbs injectors and figure I will need about 55psi at max boost.
I agree with Smitty.. you probably ought to make a jump to the next size. And compare prices with low Z and high Z and what it might take to setup the system.
Dick
Last edited by Mr Gadgets; 03-15-2008 at 01:14 PM. Reason: Noticed people were discussing it already.
03-15-2008, 02:33 PM
#30
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Thread Starter
Bob
