Is there a better Walbro pump?
08-13-2007, 07:19 PM
#16
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I agree with HOHN that running a high volume pump is not optimum. The Fass and Airdog claim that fuel pumps cause air to be entrained in the fuel and their pumps separate the air out of the fuel. I believe this is because the pump is running at full speed and whips the fuel into a froth.
Last week I received a cheap PWM motor driver kit. By using a pressure sender and this kit it is possible to run the pump at the speed needed to maintain the pressure you set but not whip the fuel up. There will be no need for a bypass regulator.
Here is a link to the manufacturer of the kit. http://www.vellemanusa.com/us/enu/pr...iew/?id=350605
If you do a search for the K8004 DC to PWM kit you will find them for less than $20.
In the next week I hope to post my experience with this kit driving an Aeromotive gerotor pump, similar to the Walbro pumps. It looks like this kit will power an electronic pressure sender and by using the pots on the PC board, makes the pressure adjustable. Just give me a few days.
Last week I received a cheap PWM motor driver kit. By using a pressure sender and this kit it is possible to run the pump at the speed needed to maintain the pressure you set but not whip the fuel up. There will be no need for a bypass regulator.
Here is a link to the manufacturer of the kit. http://www.vellemanusa.com/us/enu/pr...iew/?id=350605
If you do a search for the K8004 DC to PWM kit you will find them for less than $20.
In the next week I hope to post my experience with this kit driving an Aeromotive gerotor pump, similar to the Walbro pumps. It looks like this kit will power an electronic pressure sender and by using the pots on the PC board, makes the pressure adjustable. Just give me a few days.
from what your saying is that we will beable to adjust the pressure needed rather than shims in the fuel system so i can run a walbro at 20psi then turn it up to 40psi in i need to
08-13-2007, 07:48 PM
#18
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CTD03, yes you can turn one pot to set the minimum pressure you would ever want and another pot to set the pressure you want at the IP. This pressure can be from 0 to the maximum the pump will provide. One problem is the PWM kit will only supply 6.8 amps if you need 40 psi the pump will draw more current. It is easy to get around this problem with a few more parts but now you are getting into geek territory. It would require adding another MOSFET in parallel with the one in the kit along with a larger heat sink. For us 2nd gen VP folks the 6.8 amps will provide plenty of pump current for up to 20 psi.
08-13-2007, 08:23 PM
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08-13-2007, 08:54 PM
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But fuel REQUIREMENTS do not rise with rpm-- the fuel demand at 2000 rpm and no boost is MUCH less than 2000rpm and 40psi of boost. Yet a mechanical pump without regulation will no deliver the same volume in both circumstances.
A Mechanical setup with a bypass regulator is probably the best of all worlds, but a PWM setup on an electric pump would be even better. The PWM is much more versatile. The PWM could run anywhere from 10% to 100% duty cycle, while the mechical pump can only match engine rpm, which is comparatively a much narrower operating range.
Then you go back to cost/benefit and the mechanical setup gets another bloody nose on the value scale.
Yes, there's the argument that a mechanical setup will practically last forever.
But a large, well-made electric pump like the Aeromotive pumps or the Walbros will essentially run forever when throttled down with a PWM setup.
Run a big Aeromotive Marine pump down at 10% duty cycle, and your Cummins will wear the bores out before the pump dies!
JH
08-13-2007, 09:39 PM
#22
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Previously only available on the trans-Alaskan oil pipeline...On the subject of efficiency, I totally agree with both Hohn and Bent Valves. And I agree that the PWM setup is the cleanest solution. But - and it is important - the PWM setup must be robust enough to where it will not turn the pump on 100% if the circuitry fails, or the FP will go up to where nobody wants it - 100 psi and more. And if we were to install a failsafe overflow valve - we just lost the advantages of the simplicity, since we could have the same setup with the overflow valve without the PWM.
One advantage of PWM, one can dial the fuel pressure fromthe cab with a turn of a ****. Power freaks would love that, add a mod and dial up the FP if, God forbid, it drops down by a psi.
However, from the practical standpoint, this all is probably completely unnecessary. While efficient is usually good, what I would gain from efficiency in this case is less power usage (electrical power, that is). I will be pulling 1-2 amps rather than 7. But it makes no difference from a practical point, the truck is making tons of power and even at night with headlights running, it is not all in high demand. Even the stock LP pulled 10-12 amps, why should I worry about 7.
But since I am also an efficiency freak, I don't want the extra power and flow wasted and will put a 2 micron filter on my overflow line.
-P
08-15-2007, 12:54 PM
#24
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Here is an update on the DC to Pulse Width Modulator kit, K8004.
The intent of using this kit is to control the lift pump speed to adjust the fuel pressure to a set point you choose. To do this a pressure sender is used to modify the duty-cycle of the voltage to the pump. The kit I chose has all the things needed to do this and I had assumed it could be modified to lower the duty-cycle with a rising pressure. This negative feedback is needed to keep the pump from running at full speed all the time. The IC chip has both positive and negative inputs, which I assumed could be used for this application. Unfortunately this is not the case. After building the kit I found the SG3525 IC chip cannot be run in this way.
I got looking around for an easy answer and came across another chip, SG3537. This is a direct replacement for the SG3525 but has the correct sense to lower the duty-cycle with an increasing fuel pressure. This will be the answer for an easy PWM circuit to control the lift pump. The only problem I have now is trying to buy a small quantity of these chips. Most places only want to sell them in 1000s. But I will not give up easily; just add a few more weeks to my quest for a cheap and easy PWM circuit.
The intent of using this kit is to control the lift pump speed to adjust the fuel pressure to a set point you choose. To do this a pressure sender is used to modify the duty-cycle of the voltage to the pump. The kit I chose has all the things needed to do this and I had assumed it could be modified to lower the duty-cycle with a rising pressure. This negative feedback is needed to keep the pump from running at full speed all the time. The IC chip has both positive and negative inputs, which I assumed could be used for this application. Unfortunately this is not the case. After building the kit I found the SG3525 IC chip cannot be run in this way.
I got looking around for an easy answer and came across another chip, SG3537. This is a direct replacement for the SG3525 but has the correct sense to lower the duty-cycle with an increasing fuel pressure. This will be the answer for an easy PWM circuit to control the lift pump. The only problem I have now is trying to buy a small quantity of these chips. Most places only want to sell them in 1000s. But I will not give up easily; just add a few more weeks to my quest for a cheap and easy PWM circuit.
08-15-2007, 02:47 PM
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08-15-2007, 02:51 PM
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Not at all. The efficiency of the pump is completely unrelated.
What I'm saying is that pumping a lot more fuel than you need to-- with ANY pump-- is less efficient.
Think air compressors, for example. Most air tools run at 90psi max. So why do you need a compressor that goes to 175psi? You don't! The idea is just that the compressor won't run continuously. Far more efficient to have a 80gal tank at 120psi than a 30 gal tank at 180psi. But no one wants to give up the huge space for a massive air tank, so they crank up the pressure on a small compressor.
The most efficient way to compress air for a 90psi air tool is to continuously run a compressor at 90psi. But that doesn't give you any wiggle room and no one wants the compressor running continuously.
Taking it back to the fuel pumps, it's most efficient to pump what you need-- no more, no less. In the case of being over-pumped, this just shows up as hotter fuel temps.
..Just like an air compressor that runs at 175psi runs a lot hotter than a lower psi compressor. Compare a small Craftsman home-user compressor to a small IR home user compressor (garagemate) and you'll see the IR runs a lot lower PSI, but delivers just as much air. It runs cooler and will last a ton longer.
Sorry for the tangent, I hope it helped make the point.
JH
What I'm saying is that pumping a lot more fuel than you need to-- with ANY pump-- is less efficient.
Think air compressors, for example. Most air tools run at 90psi max. So why do you need a compressor that goes to 175psi? You don't! The idea is just that the compressor won't run continuously. Far more efficient to have a 80gal tank at 120psi than a 30 gal tank at 180psi. But no one wants to give up the huge space for a massive air tank, so they crank up the pressure on a small compressor.
The most efficient way to compress air for a 90psi air tool is to continuously run a compressor at 90psi. But that doesn't give you any wiggle room and no one wants the compressor running continuously.
Taking it back to the fuel pumps, it's most efficient to pump what you need-- no more, no less. In the case of being over-pumped, this just shows up as hotter fuel temps.
..Just like an air compressor that runs at 175psi runs a lot hotter than a lower psi compressor. Compare a small Craftsman home-user compressor to a small IR home user compressor (garagemate) and you'll see the IR runs a lot lower PSI, but delivers just as much air. It runs cooler and will last a ton longer.
Sorry for the tangent, I hope it helped make the point.
JH
08-15-2007, 02:52 PM
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Theoretical HP, Ope-- the point is that the pump is overkill for his application. Run the numbers for how much fuel you need at .4 BSFC, 7.2 lb/gal for diesel, etc.. Straight off the flow chart.
Real world, it might support only 800hp-- but that's irrelevant to the point here... The pool of 800hp trucks is bigger than ever, but still pretty small.
Real world, it might support only 800hp-- but that's irrelevant to the point here... The pool of 800hp trucks is bigger than ever, but still pretty small.
08-15-2007, 03:47 PM
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Theoretical HP, Ope-- the point is that the pump is overkill for his application. Run the numbers for how much fuel you need at .4 BSFC, 7.2 lb/gal for diesel, etc.. Straight off the flow chart.
Real world, it might support only 800hp-- but that's irrelevant to the point here... The pool of 800hp trucks is bigger than ever, but still pretty small.
Real world, it might support only 800hp-- but that's irrelevant to the point here... The pool of 800hp trucks is bigger than ever, but still pretty small.
"a regular Walbro 392 will support a 1000hp at 20psi delivery"
to dropping 200 hp
"a regular Walbro 392 will support a 800hp at 20psi delivery"
I am asking you to show/list one truck that can back up that even back up that claim.
Guys and their flow charts, I never see the any of the flow chart guys at any competitions. Just once it would be nice to see others back up their claims in the real world.
08-15-2007, 04:03 PM
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Opie I have no dog in this fight. The point is that the pump is more than a typical <450hp truck could ever need.
In my twins thread, I theorized that it would take 73lb/min of air to support 500hp at the EGTs I want. I calculated it.
Why the need to back that up?
I know you're a competitive guy (and your success speaks for itself), but I can't see how this needs any proof
Racers build racing fuel systems and street guys have street fuel systems. I'm saying the 392 is overkill for a street application and a smaller pump is probably a better fit.
What you do with a race fuel system is another matter, and if I was claiming I'd done low 12 or mid 11's on a single 392, you'd have a valid case to make someone "prove it".
Fair enough?
In my twins thread, I theorized that it would take 73lb/min of air to support 500hp at the EGTs I want. I calculated it.
Why the need to back that up?
I know you're a competitive guy (and your success speaks for itself), but I can't see how this needs any proof
Racers build racing fuel systems and street guys have street fuel systems. I'm saying the 392 is overkill for a street application and a smaller pump is probably a better fit.
What you do with a race fuel system is another matter, and if I was claiming I'd done low 12 or mid 11's on a single 392, you'd have a valid case to make someone "prove it".
Fair enough?