dubious
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posted February 14, 2009 11:59 AM
 Edited By: dubious on 14 Feb 2009 20:07
A very good read!- By Doug Meyer
Fuel pumps, injectors pressures and flow....
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running a big shot, big motor or turbo?
Just want to understand fueling issues better?
Read on
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Pumps - How they Really Work!!
by Doug Meyer
..First a little about pumps. A pump moves a fluid. It creates a flow with pressure. You can have a lot of flow at a low pressure or a little flow at a high pressure or high flow at a high pressure or low flow at low pressure. Different types of pump designs are best for each of these requirements. Examples- a centrifugal pump like the water pump on your bike creates a lot of flow at a low pressure. A gear pump like the oil pump can create a generous flow at a high pressure. Flow and pressure are generally related in that if you retard the flow, the pressure builds. Allow the flow to increase and the pressure falls. Pumps are spec’ed with a certain flow at a certain pressure. An easy example would be a bucket and a hose. Household water pressure is about 35 psi. Run a hose onto a bucket and you get a fair amount of water in there pretty quickly. Put your thumb over the end and the pressure goes up dramatically, and the flow (amount of water getting into the bucket over a given time) goes down. The “spray” is better, though (remember that). Each type of pump has it’s limitations. Pinch off the flow in a centrifugal pump and it just spins freely with no problem (and no pressure). Restrict the flow in a good gear pump and the non compressibility of the fluid can build pressure until something breaks or blows up. That’s why there are pressure relief valves in oil systems. Pumps have a flow vs. pressure efficiency curve. Turn a pump too slow and flow is very small or zero, ask it to flow too much and pressure begins to drop- it can’t “keep up”, it cavitates or can’t move the fluid fast enough to satisfy the requirement and the pressure drops.
The fuel pump in a ZX-12 is a kind of hybrid between a centrifugal vane pump and gear pump, called a friction pump. The electric motor (which is cooled by and submerged in the fuel) spins a thin plastic disc rimmed with small “teeth” like a very fine gear. This disc spins in a small plastic housing. The fuel goes to the periphery of the spinning wheel, is “grabbed” by the small teeth, spun around and forced out of the housing. It’s not exactly a positive displacement pump like a gear pump, but it’s not exactly a centrifugal pump either. It’s a little of both. Problem is, it has a pretty small sweet spot of good flow and pressure. But, that shouldn’t be a problem because a stock ZX-12 has a very predicable fuel requirement, and as you point out, the pump always spins the same speed. The pump NEEDS only to provide enough fuel to create no more than about 180 hp at no less than 47 psi. The pump does that just fine, but it does that at the very high end of it’s efficiency curve. Ask it to provide enough fuel to create 200 hp and it can barely keep up. It can do it, but let it get worn or let the fuel get hot lowering the vapor pressure, or let the injectors get “sloppy” or let any number of other factors degrade it’s performance and the flow (and pressure) drops. Less fuel means a leaner mix and soon, detonation and broken parts. How much fuel are we talking about here? The answer lies in something called Brake Specific Fuel Consumption (BSFC), which is expressed in pounds of fuel burned per horsepower per hour. Gasoline contains a pretty much fixed amount of heat energy that when “liberated” through burning is mechanically converted to horsepower. In a modern four stroke that amount is fairly constant at between .42 and .5 pounds of fuel per horsepower per hour. As an example let’s pick .5 ‘cause the math is easy. 180 hp would require .5 pounds of gas for each of 180 the hp or 90 pounds per hour (PPH). A gallon of gas weighs about 6.2 pounds so that’s 14.5 gal per hour or .24 gal. per minute at wide open. I’m told by Kawasaki engineers that the stock ZX-12 pump is a .65 liter per minute pump at 45 psi continuous. That converts to .21 gal per minute, 12.7 gallons per hour or 79 PPH. Ask it for more and you might not get it. Interestingly enough, that fuel delivery is enough for about 160 hp at .5 or at a more realistic .47, 164 hp. Guess what the average stock ZX-12 (2000/01) makes for HP? So, why not put in a different pump, one that is sized to deliver much more fuel at 50 psi. That way you are unlikely to be able to approach the point where it can’t “keep up”, where the pressure might drop a bit. The Muzzy pump flows over 350 PPH at 50 psi., enough for 700 hp. More than you need? Sure. But on a modified ZX-12 the stocker may very well be less than you need. There really isn’t anything in between that fits the physical mounting requirements.
A few words about injectors and pressure may be in order here. An electronic fuel injector is a nothing more than an electromagnetically operated solenoid valve. There are two basic varieties, “high impedance” and “low impedance”. In a high impedance injector, a current is sent to the magnetic coil in the injector which lifts a plunger and holds it open for a set period of time (in thousandths of a second or milliseconds) then cuts off and lets it close. Low impedance injectors are a little more sophisticated. They use a high current to quickly open the injector then a lower current to hold it there until closing. Better, but the “driver” circuitry and injectors are more expensive. The “open time” is expressed as a percentage of 100% (always open) and is called the duty cycle. A duty cycle of about 80% is preferred. Most OEM systems (including the 12) use the low impedance injector design. When you more flow from the pump, the only way to increase the fuel to the engine is to lengthen the injector duty cycle. A drawback to this is that the longer you hold a low impedance injector open, the longer the (high opening) current is flowing through the coils in the injector, creating electrical resistance and heat. This is a bad thing for the injector’s health. Also, the longer you have the injector open the more you put the pump into the high flow, high pressure corner of the pump’s output curve. What might help this? How about more fuel pressure? That would flow more fuel through the injector in a shorter time. That additional pressure will also make a better “spray” (see bucket example above). The pressure flow relationship is not linear. It takes four times the pressure to get two times the flow through a constant orifice. Remember, flow through an orifice is volume over time and the duty cycle controls the time. To increase the fuel flow needed on the ZX-12 when raising the power from 165 to 200, would require an 8% increase in flow through the nozzles. If it were to be done with pressure alone, without changing the duty cycle, that would take an increase in pressure of 36%. On a stock system that would necessitate an increase of fuel pressure up to 61 psi., something the stock pump is clearly not up to. Again, the “bigger” pump will allow for more fuel to be pumped at a given pressure. Increase the duty cycle (orifice size) and the pump can “keep up”.
All this talk about fuel flow and quantities makes me think about how easy it is to determine these numbers now that we have electronic fuel injection. Back in the day, to measure fuel flow mechanically we used “turbine” flow meters that put a signal to a digital indicator. WAY back in the day we actually ran a carefully measured (by weight) amount of fuel over time on the dyno and measured the consumption to figure out the BSFC. Now days it’s real easy. An injector is rated for a certain amount (in cc’s) of fuel flow at a certain pulse width (in milliseconds) do the math and you get an accurate measurement of the fuel per “squirt”. You get one squirt per injector every other revolution (1/2 the rpm). Do a little more math and you know exactly how much fuel you are using at a given rpm. Do this on a dyno, and you know how much fuel per hp and you have the BSFC.
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natural selection.....
destiny will overcome intervention.
Some are not worthy of the effort.
  
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Rook
Pro
Posts: 1125
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posted February 14, 2009 12:29 PM
Thanks for sharing, dub. That's one more thing that I will have to consider upgrading when the day of the turbo comes along.
Rook
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Bad in Black
Expert Class
Posts: 348
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posted February 14, 2009 02:07 PM
quote:
Thanks for sharing, dub. That's one more thing that I will have to consider upgrading when the day of the turbo comes along.
Rook
So there "will" be a day of the turbo for you D? Sweeett  When you go turbo if you get a good kit it'll come with everything you need. Reputable shops have everything dialed in and set-up for you.....they do all the hard, you just pay and play 
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Rook
Pro
Posts: 1125
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posted February 14, 2009 03:33 PM
^^^^I just replied on your "gauges" topic. I can't say definitely, but I would say highly likely. Lots of changes in my life going on right now so I don't know what life will hold for me two-three months down the road. NEW JOB IS A GOOD POSSIBILITY!!!!!
Rook
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LAB3
Needs a job
Posts: 2977
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posted February 14, 2009 04:46 PM
Good Read...........how low should a ZX-14 gas tank get before there is not enough fuel to cool the pump inside?? This question came up on a Corvette site about pump failures.
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bigdtd
Needs a job
Interceptors
Posts: 4209
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posted February 15, 2009 06:30 AM
great read!
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2006 Black ZX-14,6 inches over,16/42, flies out,BMC Street Filter,Brock's Street Meg,Brock's Radial Mount Strap,PClll with Race map,Dynojet LCD w/Techmount, ZX-14 fender eliminator,Pilot Power2CTs,Speedohealer,Pazzo Levers,Cox Radiator Guard, Garmin Nuvi 265WT
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dubious
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posted February 15, 2009 07:51 AM
LAB3
a gallon should be sufficient I would think.... It won't last very long if your running it hard anyway.
Guys I have pumps, regulators, injectors, and modified rails for sale in the classifieds...
This article shows you why you would, or wouldn't need them... 
____________
natural selection.....
destiny will overcome intervention.
Some are not worthy of the effort.
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LAB3
Needs a job
Posts: 2977
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posted February 15, 2009 08:08 AM
quote:
LAB3
a gallon should be sufficient I would think.... It won't last very long if your running it hard anyway.
Guys I have pumps, regulators, injectors, and modified rails for sale in the classifieds...
This article shows you why you would, or wouldn't need them...
Thanks, I am new to the ZX-14 but not new to fast bikes. I was bracket racing a 750 SOHC Honda back in the mid 70's. You and others are a big help to ZX-14 owners. I had no idea the pump was weak in a ZX-14 if ridden hard. Thanks....Louis
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dubious
Needs a life
Needs more time to ride!
Posts: 8442
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posted February 15, 2009 08:25 AM
NO NO NO
the gallon of fuel won't last long! The pump is good!
the pump in the 14 is good, i have never heard of one failing
It just would need to be upgraded to make much more than 240 HP
LOL
I am trying to sell my stuff, but would never resort to fear mongering or anything like that.
____________
natural selection.....
destiny will overcome intervention.
Some are not worthy of the effort.
|
bigdtd
Needs a job
Interceptors
Posts: 4209
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posted February 15, 2009 09:33 AM
quote:
quote:
LAB3
a gallon should be sufficient I would think.... It won't last very long if your running it hard anyway.
Guys I have pumps, regulators, injectors, and modified rails for sale in the classifieds...
This article shows you why you would, or wouldn't need them...
Thanks, I am new to the ZX-14 but not new to fast bikes. I was bracket racing a 750 SOHC Honda back in the mid 70's. You and others are a big help to ZX-14 owners. I had no idea the pump was weak in a ZX-14 if ridden hard. Thanks....Louis
the article referenced zx-12 pumps and increased fuel need at or above 200hp
____________
2006 Black ZX-14,6 inches over,16/42, flies out,BMC Street Filter,Brock's Street Meg,Brock's Radial Mount Strap,PClll with Race map,Dynojet LCD w/Techmount, ZX-14 fender eliminator,Pilot Power2CTs,Speedohealer,Pazzo Levers,Cox Radiator Guard, Garmin Nuvi 265WT
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LAB3
Needs a job
Posts: 2977
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posted February 15, 2009 10:02 AM
quote:
NO NO NO
the gallon of fuel won't last long! The pump is good!
the pump in the 14 is good, i have never heard of one failing
It just would need to be upgraded to make much more than 240 HP
LOL
I am trying to sell my stuff, but would never resort to fear mongering or anything like that.
Duh...... See what happens when I read between the lines...:-)...hey I am getting Old,...:-)
Thanks for all the information and the help with the fender braces too. Good luck with your parts for sale.
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dubious
Needs a life
Needs more time to ride!
Posts: 8442
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posted February 15, 2009 10:15 AM
quote:
quote:
quote:
LAB3
a gallon should be sufficient I would think.... It won't last very long if your running it hard anyway.
Guys I have pumps, regulators, injectors, and modified rails for sale in the classifieds...
This article shows you why you would, or wouldn't need them...
Thanks, I am new to the ZX-14 but not new to fast bikes. I was bracket racing a 750 SOHC Honda back in the mid 70's. You and others are a big help to ZX-14 owners. I had no idea the pump was weak in a ZX-14 if ridden hard. Thanks....Louis
the article referenced zx-12 pumps and increased fuel need at or above 200hp
Correct, and the requirements and issues involved with using any fuel pump not rated for the task it needs to perform.
____________
natural selection.....
destiny will overcome intervention.
Some are not worthy of the effort.
|
dubious
Needs a life
Needs more time to ride!
Posts: 8442
|
posted February 15, 2009 10:16 AM
quote:
Duh...... See what happens when I read between the lines...:-)...hey I am getting Old,...:-)
Thanks for all the information and the help with the fender braces too. Good luck with your parts for sale.
No problem, and thank you!
____________
natural selection.....
destiny will overcome intervention.
Some are not worthy of the effort.
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