This One Is For Eddie Young
08-10-2009, 02:07 PM
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This One Is For Eddie Young
Recently, Eddie Young mentioned he had saved a set of engines from a shortened life. Since that comment, I've waited for someone to ask what was meant. I guess I'm the only one in the dark.
Eddie explained he had found fuel tank pickup tubes that were to LARGE, which caused fluctuating, low fuel pressure. I'm confident that variation would or could effect several things.
It's increasingly bugged me that some fuel injected engines seem to start better and run stronger when the tanks are over half full. For some time line, probably since the modern day fuel was introduced.
We know the auto makers have pulled their hair out with various unexplainable failures until they installed fuel pumps in the tank.
Further, should sizing of the fuel pickup/fuel line size be applicable to carbs as well?
Everyone is welcome to join in, I'm confident participation would be appreciated.
Eddie explained he had found fuel tank pickup tubes that were to LARGE, which caused fluctuating, low fuel pressure. I'm confident that variation would or could effect several things.
It's increasingly bugged me that some fuel injected engines seem to start better and run stronger when the tanks are over half full. For some time line, probably since the modern day fuel was introduced.
We know the auto makers have pulled their hair out with various unexplainable failures until they installed fuel pumps in the tank.
Further, should sizing of the fuel pickup/fuel line size be applicable to carbs as well?
Everyone is welcome to join in, I'm confident participation would be appreciated.
08-10-2009, 04:14 PM
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physics gives you the answer.
given: the pump has to deliver the volume of fuel that the motor needs at wot . you determine that number from the brake specific fuel consumption numbers from the dyno. or you just estimate how many gals per hour your motor uses at wot from experience... but either way you then double that number.
that gives you a 100 % safety factor for your fuel pump selection.
now you look at your fuel pump selection specifications. all will give you gal or L/hour at a given pressure. but the number you really want is the lift capability.
in order to get a column of fluid "up" you create a negative presure above it... like sucking on a straw... but that suction has a finite value. the smaller the straw, the smaller the volume of fuel that it holds and , as such, the less it weighs. the less it weighs the less "suction" you need to raise it. the bigger it is, the more that column weighs and the more suction or lift capability the pump needs.
hi pressure vane pumps don't have much lift capability. typical diaphram pumps have a lot more. thats why all hi press efi pumps are gravity fed ( when installed properly) i.e the pumps are lower than the tank.
fluid seeks its own level.. so when the tank is full or where ever, the fuel in the pick up tube is up there as well. that means the column lift is necessarilly shorter and weighs less. if the tank is near empty and the pump lift is marginal then thats worst case and where the problems start.
the proper way to do this sort of thing is to use an accumulator.
you create a small surge tank of about a quart. you get an electric pump that has monstrous lift and use that to get the fuel out of the tank up and into the surge tank. it has a return so it doesn't pressurize. from the bottom of that tank you gravity feed the primary fuel pump for the motor. carb or efi doesn't matter. what that does is insure that the primary pump always has a clean full quart of fuel to draw from no matter what bizzareness is happining in the tank due to g forces or slosh or whatever.
as for tube size. 3/8 will supply anything in the real world and at 1/2 you increase the lift requirement by almost 100% for no material gain what so ever.
given: the pump has to deliver the volume of fuel that the motor needs at wot . you determine that number from the brake specific fuel consumption numbers from the dyno. or you just estimate how many gals per hour your motor uses at wot from experience... but either way you then double that number.
that gives you a 100 % safety factor for your fuel pump selection.
now you look at your fuel pump selection specifications. all will give you gal or L/hour at a given pressure. but the number you really want is the lift capability.
in order to get a column of fluid "up" you create a negative presure above it... like sucking on a straw... but that suction has a finite value. the smaller the straw, the smaller the volume of fuel that it holds and , as such, the less it weighs. the less it weighs the less "suction" you need to raise it. the bigger it is, the more that column weighs and the more suction or lift capability the pump needs.
hi pressure vane pumps don't have much lift capability. typical diaphram pumps have a lot more. thats why all hi press efi pumps are gravity fed ( when installed properly) i.e the pumps are lower than the tank.
fluid seeks its own level.. so when the tank is full or where ever, the fuel in the pick up tube is up there as well. that means the column lift is necessarilly shorter and weighs less. if the tank is near empty and the pump lift is marginal then thats worst case and where the problems start.
the proper way to do this sort of thing is to use an accumulator.
you create a small surge tank of about a quart. you get an electric pump that has monstrous lift and use that to get the fuel out of the tank up and into the surge tank. it has a return so it doesn't pressurize. from the bottom of that tank you gravity feed the primary fuel pump for the motor. carb or efi doesn't matter. what that does is insure that the primary pump always has a clean full quart of fuel to draw from no matter what bizzareness is happining in the tank due to g forces or slosh or whatever.
as for tube size. 3/8 will supply anything in the real world and at 1/2 you increase the lift requirement by almost 100% for no material gain what so ever.
08-10-2009, 06:52 PM
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The lift pump method (high lift pump w/ return to tank) to the small reservoir was used on the Mercury 2.5,280 EFI Outboard. The engine fuel pump drew from the reservoir. I don't recall where the engine pump returned into.
However, for some reason, Mercury discourages using the lift pump/tank for some of their other engines.
Dodge, Cummins powered trucks used lift pumps to supply their Hi Pressure injection pumps. Invariably, the Hi pressure pump failure was blamed on the lift pump. However, the lift pump may have met spec. Their other diagnosis was running the tanks low on fuel, which supports Steves statement.
Dodge finally eliminated most of the problem by using an in tank fuel pump to supply the Hi Pressure pump. It's an assumed fact, it is easier to push fluid than pull fluid.
As I know an accumulator, it is typically used as a shock absorber. The canister has two parts, one is a bladder charged to a predetermined PSI pressure and the other is a chamber fluid can move into, subject to restriction on the bladder PSI. When the fluid line pressure exceeds the system design pressure, fluid moves against the bladder pressure, thus the shock absorber.
It seems several variables may exist from boat to boat or better stated, installation to installation. Such as, distance from tank to pump, elbows, fittings, filters, line size, temperature, elevation, vents, consumption and etc. To say nothing of air leaks.
Therefore, it is agreed physics proves the pickup tube must be sized to consumption. However, what is the safest plumbing method with all variables considered ?
However, for some reason, Mercury discourages using the lift pump/tank for some of their other engines.
Dodge, Cummins powered trucks used lift pumps to supply their Hi Pressure injection pumps. Invariably, the Hi pressure pump failure was blamed on the lift pump. However, the lift pump may have met spec. Their other diagnosis was running the tanks low on fuel, which supports Steves statement.
Dodge finally eliminated most of the problem by using an in tank fuel pump to supply the Hi Pressure pump. It's an assumed fact, it is easier to push fluid than pull fluid.
As I know an accumulator, it is typically used as a shock absorber. The canister has two parts, one is a bladder charged to a predetermined PSI pressure and the other is a chamber fluid can move into, subject to restriction on the bladder PSI. When the fluid line pressure exceeds the system design pressure, fluid moves against the bladder pressure, thus the shock absorber.
It seems several variables may exist from boat to boat or better stated, installation to installation. Such as, distance from tank to pump, elbows, fittings, filters, line size, temperature, elevation, vents, consumption and etc. To say nothing of air leaks.
Therefore, it is agreed physics proves the pickup tube must be sized to consumption. However, what is the safest plumbing method with all variables considered ?
08-10-2009, 07:20 PM
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physics gives you the answer.
given: the pump has to deliver the volume of fuel that the motor needs at wot . you determine that number from the brake specific fuel consumption numbers from the dyno. or you just estimate how many gals per hour your motor uses at wot from experience... but either way you then double that number.
that gives you a 100 % safety factor for your fuel pump selection.
now you look at your fuel pump selection specifications. all will give you gal or L/hour at a given pressure. but the number you really want is the lift capability.
in order to get a column of fluid "up" you create a negative presure above it... like sucking on a straw... but that suction has a finite value. the smaller the straw, the smaller the volume of fuel that it holds and , as such, the less it weighs. the less it weighs the less "suction" you need to raise it. the bigger it is, the more that column weighs and the more suction or lift capability the pump needs.
hi pressure vane pumps don't have much lift capability. typical diaphram pumps have a lot more. thats why all hi press efi pumps are gravity fed ( when installed properly) i.e the pumps are lower than the tank.
fluid seeks its own level.. so when the tank is full or where ever, the fuel in the pick up tube is up there as well. that means the column lift is necessarilly shorter and weighs less. if the tank is near empty and the pump lift is marginal then thats worst case and where the problems start.
the proper way to do this sort of thing is to use an accumulator.
you create a small surge tank of about a quart. you get an electric pump that has monstrous lift and use that to get the fuel out of the tank up and into the surge tank. it has a return so it doesn't pressurize. from the bottom of that tank you gravity feed the primary fuel pump for the motor. carb or efi doesn't matter. what that does is insure that the primary pump always has a clean full quart of fuel to draw from no matter what bizzareness is happining in the tank due to g forces or slosh or whatever.
as for tube size. 3/8 will supply anything in the real world and at 1/2 you increase the lift requirement by almost 100% for no material gain what so ever.
given: the pump has to deliver the volume of fuel that the motor needs at wot . you determine that number from the brake specific fuel consumption numbers from the dyno. or you just estimate how many gals per hour your motor uses at wot from experience... but either way you then double that number.
that gives you a 100 % safety factor for your fuel pump selection.
now you look at your fuel pump selection specifications. all will give you gal or L/hour at a given pressure. but the number you really want is the lift capability.
in order to get a column of fluid "up" you create a negative presure above it... like sucking on a straw... but that suction has a finite value. the smaller the straw, the smaller the volume of fuel that it holds and , as such, the less it weighs. the less it weighs the less "suction" you need to raise it. the bigger it is, the more that column weighs and the more suction or lift capability the pump needs.
hi pressure vane pumps don't have much lift capability. typical diaphram pumps have a lot more. thats why all hi press efi pumps are gravity fed ( when installed properly) i.e the pumps are lower than the tank.
fluid seeks its own level.. so when the tank is full or where ever, the fuel in the pick up tube is up there as well. that means the column lift is necessarilly shorter and weighs less. if the tank is near empty and the pump lift is marginal then thats worst case and where the problems start.
the proper way to do this sort of thing is to use an accumulator.
you create a small surge tank of about a quart. you get an electric pump that has monstrous lift and use that to get the fuel out of the tank up and into the surge tank. it has a return so it doesn't pressurize. from the bottom of that tank you gravity feed the primary fuel pump for the motor. carb or efi doesn't matter. what that does is insure that the primary pump always has a clean full quart of fuel to draw from no matter what bizzareness is happining in the tank due to g forces or slosh or whatever.
as for tube size. 3/8 will supply anything in the real world and at 1/2 you increase the lift requirement by almost 100% for no material gain what so ever.
However, I will have to disagree with the 3/8" supply will feed most anything real world. If this was true all your high flow pumps would only have 3/8" inlets and outlets. no matter what your supply line, the fuel will only flow as fast as the smallest restriction in the line. Just my opinion.
08-10-2009, 07:30 PM
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I assume that most of the issues arise when the power is increased (larger fuel demand) in a given hull. As stated, there are lot's of variables as to ideal. Assuming the fuel system doesn't lose the it's prime, does the diameter of the pick up tube in the tank make much difference? If the fuel pump creates vacuum, won't the fuel flow? Steve, I do agree with that a 3/8" line will support at least 800 HP NA, assuming it is plumbed correctly. However, 1/2" doesn't seem overly large for any component in a HP fuel system (no facts, just an observation).
My seat of the pants experience simply says that if you have fuel/water separation, filtration and the necessary constant fuel pressure at WOT, you are good to go.
Cat, as you definitely aren't seat of the pants
I can't comment on how each component should be sized by the GPM required.
Does a large fuel/water separator like the Fram if mounted before the fuel pump act like a small holding tank?
My seat of the pants experience simply says that if you have fuel/water separation, filtration and the necessary constant fuel pressure at WOT, you are good to go.
Cat, as you definitely aren't seat of the pants
I can't comment on how each component should be sized by the GPM required.Does a large fuel/water separator like the Fram if mounted before the fuel pump act like a small holding tank?
08-10-2009, 08:31 PM
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The lift pump method (high lift pump w/ return to tank) to the small reservoir was used on the Mercury 2.5,280 EFI Outboard. The engine fuel pump drew from the reservoir. I don't recall where the engine pump returned into.
However, for some reason, Mercury discourages using the lift pump/tank for some of their other engines.
Dodge, Cummins powered trucks used lift pumps to supply their Hi Pressure injection pumps. Invariably, the Hi pressure pump failure was blamed on the lift pump. However, the lift pump may have met spec. Their other diagnosis was running the tanks low on fuel, which supports Steves statement.
Dodge finally eliminated most of the problem by using an in tank fuel pump to supply the Hi Pressure pump. It's an assumed fact, it is easier to push fluid than pull fluid.
As I know an accumulator, it is typically used as a shock absorber. The canister has two parts, one is a bladder charged to a predetermined PSI pressure and the other is a chamber fluid can move into, subject to restriction on the bladder PSI. When the fluid line pressure exceeds the system design pressure, fluid moves against the bladder pressure, thus the shock absorber.
It seems several variables may exist from boat to boat or better stated, installation to installation. Such as, distance from tank to pump, elbows, fittings, filters, line size, temperature, elevation, vents, consumption and etc. To say nothing of air leaks.
Therefore, it is agreed physics proves the pickup tube must be sized to consumption. However, what is the safest plumbing method with all variables considered ?
However, for some reason, Mercury discourages using the lift pump/tank for some of their other engines.
Dodge, Cummins powered trucks used lift pumps to supply their Hi Pressure injection pumps. Invariably, the Hi pressure pump failure was blamed on the lift pump. However, the lift pump may have met spec. Their other diagnosis was running the tanks low on fuel, which supports Steves statement.
Dodge finally eliminated most of the problem by using an in tank fuel pump to supply the Hi Pressure pump. It's an assumed fact, it is easier to push fluid than pull fluid.
As I know an accumulator, it is typically used as a shock absorber. The canister has two parts, one is a bladder charged to a predetermined PSI pressure and the other is a chamber fluid can move into, subject to restriction on the bladder PSI. When the fluid line pressure exceeds the system design pressure, fluid moves against the bladder pressure, thus the shock absorber.
It seems several variables may exist from boat to boat or better stated, installation to installation. Such as, distance from tank to pump, elbows, fittings, filters, line size, temperature, elevation, vents, consumption and etc. To say nothing of air leaks.
Therefore, it is agreed physics proves the pickup tube must be sized to consumption. However, what is the safest plumbing method with all variables considered ?
as for line size... forget the math... just look it up. a 5/16 line at 30 psi will move 15 gal per MINUTE. thats 5/16 not even 3/8. thats 900 gals per hour.
anybody here have a boat that can use 900 gals per hour ?
i had occassion to talk to the engineers at aeromotive the other day and it was a facinating conversation. we discussed the bsfc of most big motors and their projected fuel consumption and line size requirements... it explained why their 500 hp efi pump has 5/16 outlets.
i suggest you do the same. i recognize that when you are looking at all this monstrous hardware and then look at these seemingly wimpy looking fuel lines you get afraid.
there is no reason. just look up the truth. read the specifications. do some arithmatic. i know all that big shiny aeroquip looks very zoomy but the vast majority of it is completely unneccessary.
08-10-2009, 08:36 PM
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Ben, Thanks for your confidence....first go around in 91 stock market, I wondered if I even had shorts !!
Steve probably summarized everything as well as possible without working with known specifics. Basically, I believe he said the safe generic method is to use two separate systems that are connected. The first system sucks the fuel @ low pressure/hi flow from a low elevation and puts in another tank at a much higher elevation. The second system draws clean filtered fuel from an elevated holding tank without having to work very hard. The first system may have adequate suction to draw through filters and the various other restrictions.
One point that seems hard to dispute, as fuel is handled more it may absorb heat and foam. Cool cans may reduce the temperature, but they may not be a perfect world either.
It would be interesting to know how many engines have prematurely failed, how many vapor locks, carb issues and etc. have been caused by plumbing.
Steve probably summarized everything as well as possible without working with known specifics. Basically, I believe he said the safe generic method is to use two separate systems that are connected. The first system sucks the fuel @ low pressure/hi flow from a low elevation and puts in another tank at a much higher elevation. The second system draws clean filtered fuel from an elevated holding tank without having to work very hard. The first system may have adequate suction to draw through filters and the various other restrictions.
One point that seems hard to dispute, as fuel is handled more it may absorb heat and foam. Cool cans may reduce the temperature, but they may not be a perfect world either.
It would be interesting to know how many engines have prematurely failed, how many vapor locks, carb issues and etc. have been caused by plumbing.
08-11-2009, 01:14 AM
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Steve, your idea with the accumulator tank is a sure fire way to give the pump all the clean fuel it needs. The only problem is packaging. It would really have to be done on a boat to boat basis. It is actually similar in function to the old VST tanks in the 502 Mags. The tank was feed by a mechanical pump(diaphram) that was capable of high lift pressures. The only difference was that the high pressure pump sat in the tank, instead of beneath it.
The boat that I had problems with had a pickup that was .900". That is just to big to feed anything. I typically size my pickups based on the inlet size of the fuel pump. If the pump has a -10, then I use either a 1/2" or 5/8" pickup. I have never used over 5/8". That is what I replaced the .900" pickups with. Once the tank got below 1/2, the pumps had a hard time picking up fuel. On my efi engines, the pump cycles for 5 seconds when you turn the key on. That should be enough time to bring the fuel pressure up to operating pressure. It wouldn't below a half tank. Once you started the engine, the fuel pressure would bounce all over for at least 30 seconds. If you could keep the engine running long enough, the pump would eventually pick up the fuel. Once the pressure came up, it would hold until you shut the engine off. The new pickup fixed the problem.
I am definitely not an expert on fluid dynamics. (Steve, you seen to know a bunch more about it than me) I just use what I think to be right. If I don't know, I'll ask someone that does. Like I said, I have been able to supply everything up to 1500 hp with a 5/8" pickup.
Keep typing Steve, I'm learning more.
Eddie
The boat that I had problems with had a pickup that was .900". That is just to big to feed anything. I typically size my pickups based on the inlet size of the fuel pump. If the pump has a -10, then I use either a 1/2" or 5/8" pickup. I have never used over 5/8". That is what I replaced the .900" pickups with. Once the tank got below 1/2, the pumps had a hard time picking up fuel. On my efi engines, the pump cycles for 5 seconds when you turn the key on. That should be enough time to bring the fuel pressure up to operating pressure. It wouldn't below a half tank. Once you started the engine, the fuel pressure would bounce all over for at least 30 seconds. If you could keep the engine running long enough, the pump would eventually pick up the fuel. Once the pressure came up, it would hold until you shut the engine off. The new pickup fixed the problem.
I am definitely not an expert on fluid dynamics. (Steve, you seen to know a bunch more about it than me) I just use what I think to be right. If I don't know, I'll ask someone that does. Like I said, I have been able to supply everything up to 1500 hp with a 5/8" pickup.
Keep typing Steve, I'm learning more.
Eddie
