rate of injection, injected quantity, timing and politics.

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Above is a comparison of one of our profiles compared to a stock p-7100 cam. The bottom graph is a representation of lift vs crank angle and the graph above that is a representation of how fast the lifter is moving at any given lift. This velocity is measured in thousandths per degree. As I have time, I will go into cause and effect with different scenarios. Like "why do I not make more power when I slide my plate" "why do I need so much timing" " why does my pump builder need to know how many cc I am going to run before he builds my pump" and lastly" "why is it a bad Idea for Billary or Trump to get elected"

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Above is chart that shows a few different p-7100 lobes with the p-8600 lobe shapes overlayed. Ever wondered why the p-8600 and larger frame pumps make more hp?

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Above is a matrix that shows rpm and corresponding degrees per second on the left with microseconds of injection on the top axis and the corresponding length of injection factoring for each across the matrix. I apologize that it is sloppy, it is late and I am not going to type all of it. I hoping to show how both CR and mechanical injection differ and how they work to make better power at differing rpm. I will show how the length of injection compares in CR and p-pumps and how the CR has more of a Square wave injection even since pressure is constant and how LPC setting of the p-pump can make more or less power even though the injected quantity is the same.

which one is the politics line?

Here you go Zach.

Same idea. Sorry scooter.

On the first graph, the green line represents a LPC setting of 4.5mm. The LPC is the setting point at which injection starts. Before that the plunger is coming up but the no fuel can be injected because the fuel in the plunger is being spilled back into the fuel feed passage. At LPC, the port is closed and pressure starts building. At the end of the injection event, the high pressure is spilled back into the fuel feed passage. The more throttle you use, the plunger turns to deliver more fuel by using a Helix cut into the side of the plunger. More fuel is delivered by injecting longer and longer. The injection start is always the same relative to TDCC, but the end of injection is ever changing as you move the throttle. The more pedal the longer the injection event and the further away from TDCC the end of injection, as the piston moves further down in the power stroke. The further the piston moves down, the pressure and heat start to go down as well. Also there is less oxygen close to the nozzle. The less heat oxygen and pressure you have, the worse idea it is to inject fuel, as there is very little chance of it doing anything other than smoking and making heat. If the injector can hit the bottom of the cylinder due to a tight cone angle, then extra fuel can cool off the cylinder, as the injector is getting a lot of the oxygen. If you have a very wide cone angle and you are not able to get to all of the oxygen in the cylinder, you will see artificially high EGT as the oxygen is finally able to mix with the oxygen on the way out. This is when you see a glowing manifold and turbine housing.....

To back up a bit, you need to know that the OEM pump cam in a p-7100 has around .472" lift. At idle you are only using a small portion of the total lift. at 14-16mm of rack travel the event lasts from .160-.190" and at full throttle, 21mm of rack travel, you are still only using .250" of the .472 lift"

Faster rate of injection means you will have higher injection pressures, that the even will take less time, that you will need less total timing and that you can get more fuel in closer to TDC where fuel and air can do their thing. Since the injection event is not tied to x amount of rotation but rather how much rack travel you use. If you use less rack travel you have a shorter injection event. If you have a shorter injection event, more of the fuel can be injected into the cylinder closer to TDC where it works the best. Remember there is a delay between start of injection and start of combustion, the closer to TDC you have more oxygen in a smaller space and the higher the pressure and resulting temperature(pressure makes temp) the less delay you will have between start of injection and start of combustion. So if you want to make the event short, you cant fit much fuel in the cylinder right....right if you leave it alone. This is why people go to larger plungers every degree of rotation, they inject more fuel. So what do you do if you have a large plunger and you want more clean power....increase rate of injection! You can do this by using a "faster cam" or by using an even larger plunger. More after I go home have a beer, kiss the wife and have my morning coffee...

Sorry guys, I have spent so much time at work, I have not taken the time to learn how the interwebz and the forums work.

we got your back, Zach!

NP, if you copy the IMG for each picture that is the first step, when you paste that you will see the IMG code is surrounded but a URL code, delete that and leave everything inside the

Second picture.


Third.

Finally............... Thank you.

On the first graph notice the velocity curve on top which is expressing the lift curve at the bottom. If the LPC setting which is the green line represents start of injection, then the blue line represents end of injection at 15mm of rack travel. Notice how the velocity is rapidly decreasing as you move further to the left? This is one of the main reasons that using more rack travel by moving the plate forward will yield less power per cc than at lower rack travel. This is because even though you are injecting more fuel, it is at a lower velocity and at a greatly reduced pressure. For 12-14mm of rack travel 4.5mm-4.7mm LPC is ideal(depending on the cam profile) The longer the injection event, the earlier you need to start the injection event to keep the maximum average velocity by keeping the maximum velocity in the center of the event. this is for competition engines that know how much fuel within 50cc they are going to use. If you are going to be an economy street toy that will never see more than 15mm of rack travel, you would want to use a higher LPC , so that driving down the road, you will get the highest pressure and the shortest event which will net you the greatest part throttle efficiency.

There is a lot of information to absorb here, thanks for sharing it

Thank you for the information please keep it coming! op:

Good work and thanks for sharing.

In general what can be gained from reworking the pump cam with no other internal pump changes?

The following shows the how long it takes to inject fuel at different rack travel. This is a stock cam profile and factors for a 3.6mm LPC setting which the OEM setting on a 160hp pump. The green line is the start of injection and the blue line is the end of injection

The first is .150" long event which correlates to about 13mm of rack travel. It takes 19.09 degrees of rotation to lift .150"
The second is .200" long event which correlates to about 17mm of rack travel. it takes 24.88 degrees of rotation to lift .200"
The third is .250" long event which correlates to about 21mm of rack travel. it takes 32.13 degrees of rotation to cover .200"
Notice how on the first graph, the plunger just starts to reach max velocity by the time the event is over..... This would make a less than efficient part throttle, but it will lower NOx.

Below is a stock cam with an LPC setting of 2.5mm which is the OEM setting for a 180hp pump. At such a low LPC setting, the plunger is at a very low velocity which makes for more degrees of rotation to cover the same distance. This would equate to more Microseconds to inject the same fuel as above with the 3.6mm LPC setting. You can reference the above microseconds chart to see how this compares to CR Microseconds settings. The cool thing with mechanical injection, is that is takes the same number of degrees to inject fuel at low rpm as higher rpm if the rack travel remains constant. This is why at low rpm, the common rails do so well, they can increase rail pressure to have a very short injection event at low rpm and they can also vary when the injection event starts and ends.


You can see below that the injection event is not centered on the velocity curve.

roughly
13mm of rack travel the event takes 21.76 degrees of rotation
17mm of rack travel the event takes 27.41 degrees of rotation
21mm of rack travel the event takes 33.36 degrees of rotation

Texashighways said:

On the first graph notice the velocity curve on top which is expressing the lift curve at the bottom. If the LPC setting which is the green line represents start of injection, then the blue line represents end of injection at 15mm of rack travel. Notice how the velocity is rapidly decreasing as you move further to the left? This is one of the main reasons that using more rack travel by moving the plate forward will yield less power per cc than at lower rack travel. This is because even though you are injecting more fuel, it is at a lower velocity and at a greatly reduced pressure. For 12-14mm of rack travel 4.5mm-4.7mm LPC is ideal(depending on the cam profile) The longer the injection event, the earlier you need to start the injection event to keep the maximum average velocity by keeping the maximum velocity in the center of the event. this is for competition engines that know how much fuel within 50cc they are going to use. If you are going to be an economy street toy that will never see more than 15mm of rack travel, you would want to use a higher LPC , so that driving down the road, you will get the highest pressure and the shortest event which will net you the greatest part throttle efficiency.

Click to expand...

Just curious, how do you predict how many cc's of fuel one will need for say 1100 hp. I have always been curious how to predict fuel pump specs as well as injector orifice size for a specific power.
Better yet how can one person make 1300+ on a 12mm 215 while others can't do anything close to 1000.

Also a short version of what your saying , is use less rack travel, a larger plunger and keep the injection event short with a high pressure. Correct ?

Yes in my opinion, if you have to use more than 17mm of rack travel, I would go to a bigger plunger. After that much rack travel, you start to get diminishing returns for hp per CC. Also the longer the event, the easier to grab the fastest event as your CC window is smaller. A few things to note
- lower average velocity, the lower the average pressure.
-lower average pressure, less atomization
-Bigger delivery valves, while they allow more fuel to flow increase length of injection
- Overly large injectors, while they flow more fuel, can greatly reduce peak pressure, atomization and efficiency
- too small injectors, while they may increase peak injection pressure, may reduce total injected quantity and HP potential
-some people that use larger injectors, set pop pressure much higher to help mitigate this tradeoff

As far as how to size estimate needed CC. I have seen over 2hp per cc in the 13-16mm of rack travel range. Above that 1.6-1.7 is pretty good. just work it backwards. If I wanted to make 1100 hp, I would look to do it with the least amount of rack travel. if a 13mm was use with a fast cam, it could be done at 550cc which would be a relatively low rack travel setting. On a 12mm pump, it would most likely take 21mm of rack travel and be pretty smoky and inefficient.

As far as injector sizing, that is a relative to the size of the P&B, the rpm peak power was desired and the how many CC you are wanting to use. If you wanted to make 1100hp with a 13mm pump@ 4,000 rpm a 5x.022" might do the job. If you wanted to make the same power at 4,500 rpm, you might want a 5x.025" as peak injection pressure can get higher with rpm. Another thing to note is that different injector builders build injectors very differently. One might start cutting the bottom of the pintle or the top to achieve different goals. Although I am only a cam guy, it is my basic understanding that machining the pintle on both ends can lengthen the injection event and decrease the injection pressure while injecting more fuel per degree of rotation. If it was me, I would run larger holes with larger plungers and then when I could not safely get larger holes in the nozzle, start playing with lift as a last resort for an all out engine. That being said, injector builders have wildly varying ideas on injector function and design. Opinions are like...well you know. Another thing to note. If you are using 19-21mm of rack travel and you are still wanting more, it may benefit you to go to a very tight cone angle to still be covering the entire column of oxygen in the cylinder. The longer the injection event, the harder it is to reach all of the oxygen in the cylinder . In my mind shorter events would benefit from wider cone angles because the piston travels much less over the shorter injection and you will get more interaction with fuel and air in the very short column this way.

As rpm increases, the same amount of degrees of rotation is needed to inject an amount of fuel as long as the rack travel setting is constant. What changes is the amount of time the injection event takes and the peak pressure. As rpm increases, the pressure gets higher and higher as the time allotted for injection gets shorter.

Below is a graph of the injection event at roughly 13mm, 17mm and 21mm of rack travel with a 4.5mm LPC setting

at 13mm injection takes 17.8 degrees
at 17mm injection takes 24.3 degrees
at 21mm injection takes 32.7 degrees

Take note that 13mm of rack travel only takes 17.8 degrees not 21.76 like at the 2.5mm LPC

Also if LPC was set even further to 4.7mm it would only take

13mm would take 17.68 degrees
17mm would take 24.24 degrees
21mm would take 33.39 degrees
the 13mm and 17mm of rack travel continued to pick up speed but the 21mm rack settings start to show losses.

Would love to see how a cat 3406 pump compares as far a rack travel and fuel produced.