Lynn Larsen
Lynn Larsen
For those who don't race their GT40s and don't mind saving a buck or two, I thought I would share an economical system I have put together. The issue I was trying to deal with was my high pressure EFI fuel pump sucking air under heavy braking or sustained down hill stretches when the fuel tank being used got under ½ tank. EFI rated fuel pumps DO NOT like to pump air and it doesn't take long before doing so can destroy one of these not inexpensive units. The solution that best follows the KISS principal (and has been discussed here before) is to create a 2 stage fuel system where the first, "low pressure" stage pumps fuel from the GT40's long, skinny tanks into a smaller swirl pot or header tank from which the second, "high pressure" stage pumps fuel to the fuel rails feeding the fuel injectors. The pressure in the second stage is controlled by a bypass type fuel pressure regulator as is common with virtually all modern EFI engines.
A word about the term "high pressure" with respect to EFI fuel systems: of course, "high pressure" is a relative term. And, when compared to the ≈7 psi that carb systems run at, the ≈36 psi that EFI systems run at is relatively high. But, this is not something that should scare anyone away from working on their fuel system. After all, these pressures are those commonly found in your household, potable water system; and, most of us wouldn't consider our faucets as working under "high pressure." The mystic of the "high pressure" EFI fuel system has been perpetuated, IMHO, by the industry as more than one company has made huge amounts of money selling their "exotic" systems (he says with tongue firmly planted in cheek) for wildly inflated prices.
The trickiest part of putting this system together was, believe it or not, in picking the fuel filter to use in front of the low pressure pump. The first stage of the fuel system MUST be able to keep up with second stage to assure that the swirl pot/header tank always has enough fuel in it prevent the "high pressure" pump from sucking air: the whole reason for this exercise. The "tricky" part of this is that virtually none of the economical fuel filters that are suitable for the first stage of the system have available flow data. I called several of the companies who actually make the filters and most simply stated that they didn't have that information. For the few who gave me a number, I'd bet dollars to donuts, that it was a help desk guy taking a SWAG at the value. According to Aeromotive's FAQ, the most common error in setting up fuel systems in general is using a pre pump filter that is too fine and/or with too little surface area: they recommend 100 microns with 6 square inches for their EFI pumps. If you do a little research, you will quickly see that the value point for fuel filters is quite important because one can easily spend as much on a fuel filter as one would on a reasonably price fuel pump; there just seems to be something inherently wrong with that fact.
Heat saturation of the fuel is another issue that plays into the design of a system; but, since we are designing for a street car and not a race car, this gives a little more latitude. The second stage fuel filters sourced from Mr. Gasket* are billet aluminum units that are finned. If these are placed in or near a outside air stream (like near one of the two big rear clip scoops) this will help dissipate heat from the fuel on its way to the fuel rail. The other question raised by heat concerns is whether to route the return lines to the swirl pot/header tank or to the main tanks. Again, since we are designing for a street car and quality of the fuel for the EFI system is the major concern, it was decided to take advantage of the anti-aeration return port on the RCI 1 gallon aluminum tank being used as the header tank.
*As an aside on these second stage fuel filters: I used these on my initial, single stage EFI fuel system. However, when I bought them, they were being sold by K&N. I called K&N since I could no longer find them in catalogs or on the K&N website and I couldn't remember what the micron rating was for the pleated, stainless steel filter discs that they use. The lady at the help desk said that she no longer had data for the filters, so I asked her for the name of the supplier who K&N obviously OEMed them from. She dutifully took my name and number, saying that she would have to get back with me on that. Meanwhile, I am thinking, "yeah, right! This is the last time I'll be talking to anyone from K&N." Amazingly, about 45 minutes later, she calls back and tells me that the filters are made by Goran Products in California, Golan Products - Award winning high performance products for your racing machine, who can be reached at 310-630-5858. This would turn out to be fortuitous since Mr. Gasket, who now retails these nice looking parts, only supplies them with 10 micron filter elements. Goran can provide a 60 micron element, so I ordered two for use in the pre pump filter recalling what I had read on the Aeromotive website. (Bye the way, these filters can be assembled so that the fuel must pass through the filter or they may also be assembled so that, if the filter should become full, the fuel can bypass the filter. For a racer, this could mean the difference in finishing the race or having the engine starve for fuel and quit with the checkered flag within sight!)
Some may question the choice of the MSD EFI fuel pump and I must admit that it was probably the most edgy decision made in putting the system together. But in looking at the choices without the use of rose colored, mystical glasses and with the fact that MSD does have reputation to protect, the $95 price tag just couldn't be ignored when pumps of similar flow and pressure ratings can easily sell for 300% of this price, and some go for as high as the $800 dollar range. The biggest draw back for me was the fact that the pump employs hose barb fittings rather than the -8AN fittings I would have preferred. I did email MSD technical support to see if the fittings were replaceable, but I have not heard back from them as yet. I suppose I will have to give them a call as I have found that, in general, email tech support is a dicey proposition.
Hopefully, you will find the following diagram fairly self-explanatory. There are surely hundreds, if not thousands, of possible combinations and permutations of components that could be assembled to produce a fuel system similar to this one. So, keep in mind that this is just one of the possible ways to do it and it may not contain the trade-offs of brands, pricing and real/perceived quality that you would have made.
Regards,
Lynn
A word about the term "high pressure" with respect to EFI fuel systems: of course, "high pressure" is a relative term. And, when compared to the ≈7 psi that carb systems run at, the ≈36 psi that EFI systems run at is relatively high. But, this is not something that should scare anyone away from working on their fuel system. After all, these pressures are those commonly found in your household, potable water system; and, most of us wouldn't consider our faucets as working under "high pressure." The mystic of the "high pressure" EFI fuel system has been perpetuated, IMHO, by the industry as more than one company has made huge amounts of money selling their "exotic" systems (he says with tongue firmly planted in cheek) for wildly inflated prices.
The trickiest part of putting this system together was, believe it or not, in picking the fuel filter to use in front of the low pressure pump. The first stage of the fuel system MUST be able to keep up with second stage to assure that the swirl pot/header tank always has enough fuel in it prevent the "high pressure" pump from sucking air: the whole reason for this exercise. The "tricky" part of this is that virtually none of the economical fuel filters that are suitable for the first stage of the system have available flow data. I called several of the companies who actually make the filters and most simply stated that they didn't have that information. For the few who gave me a number, I'd bet dollars to donuts, that it was a help desk guy taking a SWAG at the value. According to Aeromotive's FAQ, the most common error in setting up fuel systems in general is using a pre pump filter that is too fine and/or with too little surface area: they recommend 100 microns with 6 square inches for their EFI pumps. If you do a little research, you will quickly see that the value point for fuel filters is quite important because one can easily spend as much on a fuel filter as one would on a reasonably price fuel pump; there just seems to be something inherently wrong with that fact.
Heat saturation of the fuel is another issue that plays into the design of a system; but, since we are designing for a street car and not a race car, this gives a little more latitude. The second stage fuel filters sourced from Mr. Gasket* are billet aluminum units that are finned. If these are placed in or near a outside air stream (like near one of the two big rear clip scoops) this will help dissipate heat from the fuel on its way to the fuel rail. The other question raised by heat concerns is whether to route the return lines to the swirl pot/header tank or to the main tanks. Again, since we are designing for a street car and quality of the fuel for the EFI system is the major concern, it was decided to take advantage of the anti-aeration return port on the RCI 1 gallon aluminum tank being used as the header tank.
*As an aside on these second stage fuel filters: I used these on my initial, single stage EFI fuel system. However, when I bought them, they were being sold by K&N. I called K&N since I could no longer find them in catalogs or on the K&N website and I couldn't remember what the micron rating was for the pleated, stainless steel filter discs that they use. The lady at the help desk said that she no longer had data for the filters, so I asked her for the name of the supplier who K&N obviously OEMed them from. She dutifully took my name and number, saying that she would have to get back with me on that. Meanwhile, I am thinking, "yeah, right! This is the last time I'll be talking to anyone from K&N." Amazingly, about 45 minutes later, she calls back and tells me that the filters are made by Goran Products in California, Golan Products - Award winning high performance products for your racing machine, who can be reached at 310-630-5858. This would turn out to be fortuitous since Mr. Gasket, who now retails these nice looking parts, only supplies them with 10 micron filter elements. Goran can provide a 60 micron element, so I ordered two for use in the pre pump filter recalling what I had read on the Aeromotive website. (Bye the way, these filters can be assembled so that the fuel must pass through the filter or they may also be assembled so that, if the filter should become full, the fuel can bypass the filter. For a racer, this could mean the difference in finishing the race or having the engine starve for fuel and quit with the checkered flag within sight!)
Some may question the choice of the MSD EFI fuel pump and I must admit that it was probably the most edgy decision made in putting the system together. But in looking at the choices without the use of rose colored, mystical glasses and with the fact that MSD does have reputation to protect, the $95 price tag just couldn't be ignored when pumps of similar flow and pressure ratings can easily sell for 300% of this price, and some go for as high as the $800 dollar range. The biggest draw back for me was the fact that the pump employs hose barb fittings rather than the -8AN fittings I would have preferred. I did email MSD technical support to see if the fittings were replaceable, but I have not heard back from them as yet. I suppose I will have to give them a call as I have found that, in general, email tech support is a dicey proposition.
Hopefully, you will find the following diagram fairly self-explanatory. There are surely hundreds, if not thousands, of possible combinations and permutations of components that could be assembled to produce a fuel system similar to this one. So, keep in mind that this is just one of the possible ways to do it and it may not contain the trade-offs of brands, pricing and real/perceived quality that you would have made.
Regards,
Lynn