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Originally Posted by Mr Gadgets
(Post 2485716)
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 |
Bob,
I have always removed the vaccuum line to the regulator, keeping a solid psi. My Cutler used to hunt around, so I left it at one psi.. I guess in your situation (Smitty has more experience with the Mefi) you have to figure out what flow is needed at max power. Then work backwards from there. What ever boost you have has to be added to the psi that gives you the correct fuel flow. From there if you pull a vaccuum at idle the regulator will follow what is needed. Two schools of thought: Too much psi at idle and you pulse width may have to be reduced below min open times, to get the motor lean enough to idle clean. With the regulator, you end up lowering fuel psi/flow, now you have longer PW and are still controlling the mixture, instead of running rich because you cant open and close it for such a short PW. So less psi at idle is good, to a point. At some point the fuel will dribble out of the injector instead of spraying. With a regulator attached to the manifold, it will end up with what it is depending on manifold air pressure, be it boost or vaccuum. Check this site out. http://www.megamanual.com/v22manual/minj.htm#size The calcultor doesnt allow u to change bsfc, but there is a formula that you can do that with. A 63# inj with 53 psi should flow 69.5#. Working with their formulas, 850hp would need 79.6#/hr. That would be figuring .6 bsfc and 80% duty cycle. Moving the numbers around.. .55 bsfc and 85% duty cycle.. I calculate a 68.75#/hr.. But I think that is cutting things too close. More psi..?? Go check it out, see what you come up with. When you are on the dyno, it should tell you what fuel the motor needs to live.. Hope this helps. Dick They give formulas and calculators for sizing. The Megasquirt is the ECU I am running. A wealth of knowledge there. http://www.witchhunter.com/injectorcalc1.php4 another calculator site. |
Originally Posted by Mr Gadgets
(Post 2486247)
Bob,
I have always removed the vaccuum line to the regulator, keeping a solid psi. My Cutler used to hunt around, so I left it at one psi.. I guess in your situation (Smitty has more experience with the Mefi) you have to figure out what flow is needed at max power. Then work backwards from there. What ever boost you have has to be added to the psi that gives you the correct fuel flow. From there if you pull a vaccuum at idle the regulator will follow what is needed. Two schools of thought: Too much psi at idle and you pulse width may have to be reduced below min open times, to get the motor lean enough to idle clean. With the regulator, you end up lowering fuel psi/flow, now you have longer PW and are still controlling the mixture, instead of running rich because you cant open and close it for such a short PW. So less psi at idle is good, to a point. At some point the fuel will dribble out of the injector instead of spraying. With a regulator attached to the manifold, it will end up with what it is depending on manifold air pressure, be it boost or vaccuum. Check this site out. http://www.megamanual.com/v22manual/minj.htm#size The calcultor doesnt allow u to change bsfc, but there is a formula that you can do that with. A 63# inj with 53 psi should flow 69.5#. Working with their formulas, 850hp would need 79.6#/hr. That would be figuring .6 bsfc and 80% duty cycle. Moving the numbers around.. .55 bsfc and 85% duty cycle.. I calculate a 68.75#/hr.. But I think that is cutting things too close. More psi..?? Go check it out, see what you come up with. When you are on the dyno, it should tell you what fuel the motor needs to live.. Hope this helps. Dick They give formulas and calculators for sizing. The Megasquirt is the ECU I am running. A wealth of knowledge there. http://www.witchhunter.com/injectorcalc1.php4 another calculator site. I want this correct the first time I will spend hours doing my homework not to break it. Bob |
Originally Posted by Mr Gadgets
(Post 2486247)
Bob,
I have always removed the vaccuum line to the regulator, keeping a solid psi. My Cutler used to hunt around, so I left it at one psi.. I guess in your situation (Smitty has more experience with the Mefi) you have to figure out what flow is needed at max power. Then work backwards from there. What ever boost you have has to be added to the psi that gives you the correct fuel flow. From there if you pull a vaccuum at idle the regulator will follow what is needed. Two schools of thought: Too much psi at idle and you pulse width may have to be reduced below min open times, to get the motor lean enough to idle clean. With the regulator, you end up lowering fuel psi/flow, now you have longer PW and are still controlling the mixture, instead of running rich because you cant open and close it for such a short PW. So less psi at idle is good, to a point. At some point the fuel will dribble out of the injector instead of spraying. With a regulator attached to the manifold, it will end up with what it is depending on manifold air pressure, be it boost or vaccuum. Check this site out. http://www.megamanual.com/v22manual/minj.htm#size The calcultor doesnt allow u to change bsfc, but there is a formula that you can do that with. A 63# inj with 53 psi should flow 69.5#. Working with their formulas, 850hp would need 79.6#/hr. That would be figuring .6 bsfc and 80% duty cycle. Moving the numbers around.. .55 bsfc and 85% duty cycle.. I calculate a 68.75#/hr.. But I think that is cutting things too close. More psi..?? Go check it out, see what you come up with. When you are on the dyno, it should tell you what fuel the motor needs to live.. Hope this helps. Dick They give formulas and calculators for sizing. The Megasquirt is the ECU I am running. A wealth of knowledge there. http://www.witchhunter.com/injectorcalc1.php4 another calculator site. |
Originally Posted by Mr Gadgets
(Post 2485716)
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 Let's pretend I go this route. What can I expect to spend and what about the computer. Bob |
Seems to me, we all spend a ton of money building these blower motors. If they are done right they are capable of over 2 HP per cubic inch. We run them hard, we expect them to live. The most important part is the fuel system.
|
Originally Posted by Mr Gadgets
(Post 2485716)
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 |
Originally Posted by RBeyer
(Post 2485803)
I appreciate all of the feedback. The calculator is interesting but does not allow for increased fuel pressure. Smitty and Dick, so if I go with the 63lb and run my current fuel setup (Aeromotive red with vacuum increase) I should be in good shape? I currently run 36 psi at idle. will that need to be changed.
Bob http://www.csgnetwork.com/fiflowcalc.html |
Originally Posted by RBeyer
(Post 2485805)
The increased power draw at WOT would also explain my huge voltage drop trying to trim at WOT. Correct?
|
Originally Posted by RBeyer
(Post 2485803)
I appreciate all of the feedback. The calculator is interesting but does not allow for increased fuel pressure. Smitty and Dick, so if I go with the 63lb and run my current fuel setup (Aeromotive red with vacuum increase) I should be in good shape? I currently run 36 psi at idle. will that need to be changed.
Bob http://www.aeromotiveinc.com/product...sub=1&prod=164 click on "specs" after you open the aeromotive page and you will see a flow table with voltage vs ouput pressure vs lbs per hr Smitty |
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