1600cc

[Mirage2LTurbo]

True, but there is a such thing as minimum injector pulse width and accelerator "pump" enrichment. This is where the delimma is if you try to retain a fairly stock idle. At a base rail pressure of 35 psi the lowest I could get my idle with out an obscene 10:1 a/f ratio was 1600RPM. Dropping the pressure to 22psi allowed me to get down to 1200RPM.

Maybe you should consider better engine management. I idle 1680cc injectors at 750rpm, 14.7:1a/f. It will idle lower than that at 14.7:1, but the car wants to die and you gotta throw a bunch of timing in to keep her alive.

 

[Mirage2LTurbo]

Dont forget that the cosmo pump being used essentially as a lift pump will be running at very low pressure. Less than 5 psi most likely, but I dont have a flow chart for the cosmo handy. I ran the numbers on a 255 at 0 psi, and it just about matches the output of the A1000 at 70 psi I'm assuming at 0 psi the cosmo will outflow the A1000 at 70 psi, thereby providing slight pressure at the main pump eliminatin the need for gravity feed. The purpose of a lift pump is to supply slight head pressure at the main high pressure pump, the way diesel setups work.

Good point, I'll have to do some research on this. I sounds like it would twerk

 

[1fast97gsx]

You mean, sort of like the one he ALREADY POSTED IN THIS THREAD?

Look on page 1.

yea I guess it would help if I didn't skip right to the 2nd page ...

 

[blue1]

Ok to start, i am running a bosch 450hp pump while under 18psi of boost. it is feed by a carter 110 gph into a 2 litre surge tank for my running around upto 18psi. i have another 450hp pump that picks from the rear of the main fuel tank which comes in at 18psi, 100% load controlled by a standalone ECU, which has it's own fuel line to a filter just before the rail, both systems are on -6 lines to a home made fuel rail with a 1" bore. base fuel pressure is set at 42psi and i am running a malpassi rising rate reg' so for every 1 psi of boost i am getting 1 psi of more fuel pressure!. it has a -5 return line back to the surge tank and from the surge tank back to the fuel tank with a -6 overflow this gives me no pressure build up in the surge tank! Both pumps have -8 pick ups by the way.

At the moment i am only running 450cc inj' in the primarys with two more in staged which come in at 85% load and above 5500rpm (controlled by ECU) i have had any prob's with detonation with the two litre yet at 23psi! but going all out with a 4g64 hybrid to 30's. 343rwp is ok at the moment but chasing 600! i just want the fastest minitruck in Australia.

At the moment i am trying to buy to buy 1600's out of fuel injector clinic and cash flow.

Playing on DSM tuners and the AEM site has helped no end (thanks), in Australia everything seems to be a secret (bunch of wankers). will keep you's guys posted on my triumph's at the dyno.

 

[Mirage2LTurbo]

Your setup sounds cool, like a TON of overkill especially for your setup. Unless you are hardcore roadracing/autox/rally, I don't see a ned for the surge tank. You don't see pro-drag racers running them, and I have yet to see any autocrossers run them. maybe rally/road racers do, I don't know. It is an interesting concept though.. we'll just agree to disagree

I think your setup could be a lot better controlled by a single set of injectors, but more power to you to run staged. Got any pics of your setup?

 

[Kevin Jewer]

Good point, I'll have to do some research on this. I sounds like it would twerk

Not to get too far OT, but I just thought about this some more. At 43 psi the A1000 is going to flow a lot of fuel. 115 gph to be exact. Thats 435 lph. The walbro is rated to 85 gph at zero psi. So at WOT you would be fine (A1000 at 70 psi = ~81 gph), but at idle and cruise the A1000 would be pulling a vacuum. Hmm. A fuel cell is starting to look more and more attractive...

It would suck for daily driving unless I got a GM sender and GM fuel level guage (I dont imagine they are the same type as ours). With a pair of bypass valves from barry grant (IIRC) for belt driven pumps, you could run both the stock setup and a 5 gallon cell for race gas. Seems the 255 standard flows ~55 gph at 20 psi boost, or enough for 60 lbs/min at 11:1 AFR. More than I could flow at such low boost.

This sucks. I might just get a 255HP and hope I dont outrun that anytime soon. I'm tired of incremental upgrades though, I'd rather be done with it. NEvermind, at 12:1 the HP is only goof to 66 lbs/min, and I'm already at 64. More boost will just make it useless again. Back to the fuel cell....

 

[Mirage2LTurbo]

Not to get too far OT, but I just thought about this some more. At 43 psi the A1000 is going to flow a lot of fuel. 115 gph to be exact. Thats 435 lph. The walbro is rated to 85 gph at zero psi. So at WOT you would be fine (A1000 at 70 psi = ~81 gph), but at idle and cruise the A1000 would be pulling a vacuum. Hmm. A fuel cell is starting to look more and more attractive...

It would suck for daily driving unless I got a GM sender and GM fuel level guage (I dont imagine they are the same type as ours). With a pair of bypass valves from barry grant (IIRC) for belt driven pumps, you could run both the stock setup and a 5 gallon cell for race gas. Seems the 255 standard flows ~55 gph at 20 psi boost, or enough for 60 lbs/min at 11:1 AFR. More than I could flow at such low boost.

This sucks. I might just get a 255HP and hope I dont outrun that anytime soon. I'm tired of incremental upgrades though, I'd rather be done with it. NEvermind, at 12:1 the HP is only goof to 66 lbs/min, and I'm already at 64. More boost will just make it useless again. Back to the fuel cell....

If my car was a street car, I would have gotten a 12-16gallon cell w/sending unit. Make sure if you get a cell, get one with the sending unit in it already.. they are a PITA. Summit has awesome deals on them too

 

[GRNDSM]

To start with, A1000 is not a very good street pump... That thing is like having an extra engine running...

 

[Mirage2LTurbo]

To start with, A1000 is not a very good street pump... That thing is like having an extra engine running...

Works fine for me, it is a bit loud, but it doesn't quite overcome the exhaust

 

[4SFED4]

Maybe you should consider better engine management. I idle 1680cc injectors at 750rpm, 14.7:1a/f. It will idle lower than that at 14.7:1, but the car wants to die and you gotta throw a bunch of timing in to keep her alive.

If it was a daily driver I would, but as long as it comes up on boost good and runs right under boost why spend another $2K on a new managment system.

 

[Mirage2LTurbo]

If it was a daily driver I would, but as long as it comes up on boost good and runs right under boost why spend another $2K on a new managment system.

How is your in boost management/tuning?

 

[Kevin Jewer]

My car vibrates every possible interior piece, its one big low quality loudspeaker. I wont mind the noise, or what I hear of it. Mirage, I was literally just dropping a duece, taking another look at the summit 16 gallon with GM sendor and foam for 170. Gonna bust out the tape measure and see where I can stash it. Now that I pulled the head and know for sure my motor is toast, I have all winter to do it the right way.

 

[4SFED4]

How is your in boost management/tuning?

I use a Hallman MBC in conjunction with a staged bleed off to achive 35psi maximum boost without spiking. My fuel map is mainly dedicated to the 0-20 psi range and the rest of the areas are tuned statically. I use the bottom line for idle control and the accelerator "pump" control to handle increaed fuel demand until the intake system reaches atmospheric pressure. After it sees 20 psi, 35psi comes on almost instantly, so I tune for peak boost at that point, since the rich area is passed very quickly and unnoticed. I also have a global adjustment knob that allows me to add or remove up to 10% of fuel to easily compensate for different weather conditions without having to hook up the laptop. I use an Innovate LM-1 wideband/datalogger to tune with.

 

[crankbender]

Sorry for my absence I have been very very busy.

A few questions and clarification.

1) Did you say you are making 400+ AWHP on 15PSIG- of boost?

2) We have a 4 cylinder engine. We run 4 injectors fired independently. assuming perfect seperation between the injectors if you are running 25% duty cycle or less you are firing a max of 1 injector at a time. 25%-50% a max of 2 injectors at a time. 50%-75% 3 injectors at a time. 75%-100% you are running up to 4 injectors at the same time.

This means that almost all modified DSMs are running 2-4 injectors at the same time...food for thought.

3) You will puddle on the valves at higher RPM levels. This is mostly unavoidable as the flow during the time the valves are open just isn't enough. Your AEM manual goes into this.

4) Tapping the return line of the fuel rail (after the fpr) is done to ensure that you are getting return flow. If you ever lack flow in this line you are not getting enough fuel. This is the reason for putting a flow meter in the line.

5) Because of the flow resistance (head loss) caused by the lines and connections it is possible for your fuel pressure gauge to be way off if not tapped directly into the fuel rail.

>Let's say that all 4 injectors are open

But they never open all at once!!! So this is a moot point

And now that you brought it up, larger injectors will stay open for less time, allowing the same amount of fuel to escape. That means two things:

a. A portion of your fuel rail will be emptied quicker
b. You have more time to refill the portion of your fuel rail

Which one will prevail will largely depend on the size of your fuel rail, explaining why some people eventually move onto larger fuel rail. But unless you are dealing with extra small rails, I can see “b” being more beneficial for your fuel supply. In ether case, I do not think that going to a larger injector will put more strain the fuel pump.

Leon

But they will be open at the same time (see above and below).

GAS in essentially an incompressible fluid. This means that you can not "empty" any part of the rail and don't refil it... Essentially your fuel system is dynamic and will match flow to pressure at all times. This causes some interesting things.

at 8000 RPMs it takes approximately 16ms(rounded to a multiple of 4 for the following explanation) for the cam to make 1 revolution. now lets say that each injector is open for 6 ms.

time(ms) open injectors.
0----------------1,4
1----------------1,4
2----------------1
3----------------1
4----------------1,2
5----------------1,2
6----------------2
7----------------2
8----------------2,3
9----------------2,3
10---------------3
11---------------3
12---------------3,4
13---------------3,4
14---------------4
15---------------4

As you can see your flow rate has to double or be cut in half ever 2ms....that is really really fast. I can't really explain how fast that is for an analog system.

Now if your fuel system is not capable of flowing enough for the time of the max load you will briefly experience a loss of pressure in the fuel rail which will be corrected 2 ms later as the injector closes. THIS IS OFTEN TOO FAST FOR A FUEL PRESSURE GAUGE TO SHOW. This means that you could be experiencing loss of fuel pressure and not know it.

Now lets look at what happens if your injectors are open for 9ms.

0----------134
1----------14
2----------14
3----------14
4----------124
5----------12
6----------12
7----------12
8----------123
9----------23
10---------23
11---------23
12---------234
13---------34
14---------34
15---------34

as you can see the pulsation is even more eratic now. For refrence you are only running 56% duty cycle and you have 3 injectors open at one time .

The more I think about it, the more I like the idea of larger injectors. If you have “maxed out” 800cc injectors (which have gone static) and a pump that is on the verge if being “maxed out”, you will have a hard time supplying injectors which are down the stream. That is when people end up with #1 cylinder lean condition.

This is a false assumption. Fluid does not flow this way in reality. What actually happens is that you have a lower velocity at the end of the rail and therefore a lower dynamic pressure. This causes less fuel to enter that cylinder. It is not that you don't have enough pump. All a larger pump does is cause more fuel to be running through the entire rail and out the return line. This causes the % change in velocity along the rail to be lower. You have to remember that fuel systems MUST be looked at as dynamic systems and can't be simplified to static systems easily (you can simplify by looking at instants in time and doing the dynamic calculations with the known flow).

I will try and keep a closer eye on this thread.

 

[Mirage2LTurbo]

Sorry for my absence I have been very very busy.

A few questions and clarification.

1) Did you say you are making 400+ AWHP on 15PSIG- of boost?

2) We have a 4 cylinder engine. We run 4 injectors fired independently. assuming perfect seperation between the injectors if you are running 25% duty cycle or less you are firing a max of 1 injector at a time. 25%-50% a max of 2 injectors at a time. 50%-75% 3 injectors at a time. 75%-100% you are running up to 4 injectors at the same time.

This means that almost all modified DSMs are running 2-4 injectors at the same time...food for thought.

3) You will puddle on the valves at higher RPM levels. This is mostly unavoidable as the flow during the time the valves are open just isn't enough. Your AEM manual goes into this.

4) Tapping the return line of the fuel rail (after the fpr) is done to ensure that you are getting return flow. If you ever lack flow in this line you are not getting enough fuel. This is the reason for putting a flow meter in the line.

5) Because of the flow resistance (head loss) caused by the lines and connections it is possible for your fuel pressure gauge to be way off if not tapped directly into the fuel rail.



But they will be open at the same time (see above and below).

GAS in essentially an incompressible fluid. This means that you can not "empty" any part of the rail and don't refil it... Essentially your fuel system is dynamic and will match flow to pressure at all times. This causes some interesting things.

at 8000 RPMs it takes approximately 16ms(rounded to a multiple of 4 for the following explanation) for the cam to make 1 revolution. now lets say that each injector is open for 6 ms.

time(ms) open injectors.
0----------------1,4
1----------------1,4
2----------------1
3----------------1
4----------------1,2
5----------------1,2
6----------------2
7----------------2
8----------------2,3
9----------------2,3
10---------------3
11---------------3
12---------------3,4
13---------------3,4
14---------------4
15---------------4

As you can see your flow rate has to double or be cut in half ever 2ms....that is really really fast. I can't really explain how fast that is for an analog system.

Now if your fuel system is not capable of flowing enough for the time of the max load you will briefly experience a loss of pressure in the fuel rail which will be corrected 2 ms later as the injector closes. THIS IS OFTEN TOO FAST FOR A FUEL PRESSURE GAUGE TO SHOW. This means that you could be experiencing loss of fuel pressure and not know it.

Now lets look at what happens if your injectors are open for 9ms.

0----------134
1----------14
2----------14
3----------14
4----------124
5----------12
6----------12
7----------12
8----------123
9----------23
10---------23
11---------23
12---------234
13---------34
14---------34
15---------34

as you can see the pulsation is even more eratic now. For refrence you are only running 56% duty cycle and you have 3 injectors open at one time .



This is a false assumption. Fluid does not flow this way in reality. What actually happens is that you have a lower velocity at the end of the rail and therefore a lower dynamic pressure. This causes less fuel to enter that cylinder. It is not that you don't have enough pump. All a larger pump does is cause more fuel to be running through the entire rail and out the return line. This causes the % change in velocity along the rail to be lower. You have to remember that fuel systems MUST be looked at as dynamic systems and can't be simplified to static systems easily (you can simplify by looking at instants in time and doing the dynamic calculations with the known flow).

I will try and keep a closer eye on this thread.

1) Yes

2) No, IDC is the result of the calculation of the time that one injector is open for one firing of the engine. Therefore, if it is 25%, each injector would be open 25% for each firing cycle. I have no idea what you're trying to say in the rest of that post. There is also Injector Duty mean cycle, which shows the average cycle of all the injectors at a given point.

3) This is the point of high lift, long duration cams. I do not believe it puddles anything substantially.

4) This is not needed. See below.

5) The pressure on a rail is regulated by the FPR sitting either at the end of the rail (stock), or a foot from the end of the rail (aftermarket). Since fuel is incompressible like you said, the pressure is constant from the regulator to the rail (and back even farther).

6) My FPR gauge will show a decrease in pressure, and here's why. If your injectors do overrun your pump for that split second, there is not going to be a "recovery" time where the pump can catch up because more injectors are going to be firing at that same or greater duty cycle. This would cause a rapid decrease in pressure (and also an increase in afr)

7) As I said before, the pressure is regulated away from the rail. There is no pressure differences worth talking about, or that could affect your tuning as long as you are not over running your pump. Fuel systems can be easily shown as static because there is only a set amount of fuel entering hte engine (IDC). The pressure is constant on the rail,so the same amount enters the engine every time. THe pressure difference betweent he manifold and injector is also constant, which is the point of a rising rate regulator, so this further proves my point.

 

[crankbender]

1) Yes

WOW. have you dynoed the car yet?

2) No, IDC is the result of the calculation of the time that one injector is open for one firing of the engine. Therefore, if it is 25%, each injector would be open 25% for each firing cycle. I have no idea what you're trying to say in the rest of that post. There is also Injector Duty mean cycle, which shows the average cycle of all the injectors at a given point.

The IDC is that percentage of time the injector is open for the entire cycle of the engine. That is 4 firings...1 on each cylinder. I do believe that I explained rather well in the post above if you would look at where I mapped out the firing during a 16ms cycle. You are using an EMS correct. To prove that the readings you are getting are as I have explained I have added an excerpt from their manual.

AEM EFI Basics V1.3.doc pg 39

High injector duty cycle referrers to the amount of time required to inject sufficient fuel into the engine relative to engine speed. Consider that at 6000 RPM an engine has 10 milliseconds (Ms) to complete a revolution (360° rotation) and 20 Ms to complete one cycle (2 complete revolutions). This means that the injector cannot be open more than 20 Ms at 6000 RPM. If the injector needs to be open 20 Ms to provide adequate fuel to the engine, then the duty cycle in this example would be 100%. This condition is known as having the injector go static, which means that it remains fully open with no closing time between injections. At this point there is no appreciable fuel control via the ECU, and the amount of fuel quantity delivered is controlled by the fuel pressure and static flow of the injector.

3) This is the point of high lift, long duration cams. I do not believe it puddles anything substantially.

Once again from the ems manual

Getting back to fuel injector timing and delivery, if the cam has 270° duration on the inlet lobe, then it takes 7.5 Ms for the valve to open and close at 6000 RPM. As we stated earlier, the time to inject fuel diminishes as engine speed increases. This means that we have to start the fuel injection event sooner as engine speed increases, and eventually there is not going to be enough time to fully inject the fuel into the combustion chamber. At this point the injector will begin to deposit fuel on the backside of the inlet valve, which will be consumed on the next cycle for the given cylinder. The air speed at this point is great enough that there is shearing action on the wetted surface of the valve seat/head, and with the high flow of air fuel atomization occurs.

Think about it. With 260 degrees of the intake valve you have the intake valve open for 72% of the inake stroke revolution of that piston. This converts to 36% of the entire engine cycle. This means that if you have a duty cycle over 36% you have to puddle. There is no magic here you can not use more time than is there. Well maybe you can at the speed of light....but that is because Einstein postulated you would actually go back in time.

4) This is not needed. See below.

5) The pressure on a rail is regulated by the FPR sitting either at the end of the rail (stock), or a foot from the end of the rail (aftermarket). Since fuel is incompressible like you said, the pressure is constant from the regulator to the rail (and back even farther).

Static pressure may be constant but dynamic pressure is NOT if you have a pump that is inadequate. This is one of the reasons you have a pressure/volume curve.

Not being condecending here in any way but I have to ask so that we can be speaking on the same level. Do you have any formal education on thermal fluid sciences? Or do you have a good grasp on the basic Bernoulli equation? If not I can explain it if you would like.

6) My FPR gauge will show a decrease in pressure, and here's why. If your injectors do overrun your pump for that split second, there is not going to be a "recovery" time where the pump can catch up because more injectors are going to be firing at that same or greater duty cycle. This would cause a rapid decrease in pressure (and also an increase in afr)

No they will not. Look again at my post. Here is the section.

0----------------1,4
1----------------1,4
2----------------1
3----------------1
4----------------1,2
5----------------1,2
6----------------2
7----------------2
8----------------2,3
9----------------2,3
10---------------3
11---------------3
12---------------3,4
13---------------3,4
14---------------4
15---------------4

Now lets assume thta your pump can flow enough fuel to hold the pressure constant if you have 1.5 injectos open at the same time. That is to say that the pump can flow 1.5 times what 1 injector can at the given pressure. Now as the second injector fires the pressure and volume flow through each injector decrease. This occurs for approximately 2ms. Now the second injector closes and the flow rate is immediately decreased. The dynamic pressure (V^2/2) will increase the static pressure very quickly back to the original static pressure and the fpr will vent off the extra fuel. what you end up with is a controlled fuel flow for 2ms followed by a decreased flow for each injector for 2ms. Your fuel pressure gauge may not be physically capable of showing a change this fast. Combine this with historesis effects and you can get a fuel pressure gauge that stagnates at the peak pressure reached during a cycle.

7) As I said before, the pressure is regulated away from the rail. There is no pressure differences worth talking about, or that could affect your tuning as long as you are not over running your pump. Fuel systems can be easily shown as static because there is only a set amount of fuel entering hte engine (IDC). The pressure is constant on the rail,so the same amount enters the engine every time. THe pressure difference betweent he manifold and injector is also constant, which is the point of a rising rate regulator, so this further proves my point.

It can not be measured as a static system because the fuel in all parts of the system are not moving at the same velocity. I have also shown that you can be overrunning your pump during part of the cycle and not know it. The same is true for the FPR...Most FPRs are not capable of compensating for the dynamic part of pressure. Therefore you regulate the static part of the pressure and velocity changes can cause havoc on the system.

 

[Mirage2LTurbo]

WOW. have you dynoed the car yet?

You're one for the books, you figure it out based on fuel consumption and air flow.

The IDC is that percentage of time the injector is open for the entire cycle of the engine. That is 4 firings...1 on each cylinder. I do believe that I explained rather well in the post above if you would look at where I mapped out the firing during a 16ms cycle. You are using an EMS correct. To prove that the readings you are getting are as I have explained I have added an excerpt from their manual.

AEM EFI Basics V1.3.doc pg 39

Just because I'm running an EMS doesn't mean I have some POS AEM system running my car. I prefer to have a standalone that doesn't just forget my map and forget to either a) turn on the fuel pump when I turn the car on or b) not turn my fuel pump off when the key isn't in it. Before you defend the AEM, realize I have seen all 3 of these situations in person.

Once again from the ems manual

Think about it. With 260 degrees of the intake valve you have the intake valve open for 72% of the inake stroke revolution of that piston. This converts to 36% of the entire engine cycle. This means that if you have a duty cycle over 36% you have to puddle. There is no magic here you can not use more time than is there. Well maybe you can at the speed of light....but that is because Einstein postulated you would actually go back in time.

Oh noes! More theory on how my engine works. I can't disprove your numbers, that's the difference between reality and theory. In reality, if the puddling occurs like you say, it would puddle less on my larger injectors than on a set of smaller ones becuase I can use less duty cycle than a set of 950's, per say.

Static pressure may be constant but dynamic pressure is NOT if you have a pump that is inadequate. This is one of the reasons you have a pressure/volume curve.

Not being condecending here in any way but I have to ask so that we can be speaking on the same level. Do you have any formal education on thermal fluid sciences? Or do you have a good grasp on the basic Bernoulli equation? If not I can explain it if you would like.

No, I honestly don't. I understand the pressure/volume maps, and if you have a fuel pump that CAN FLOW enough fuel for what you require, then pressure is constant. We're talking about regulating the pressure at most 18 inches from the #1 cylinder, there is not going to be anything noticeable in that span.

No they will not. Look again at my post. Here is the section.

Now lets assume thta your pump can flow enough fuel to hold the pressure constant if you have 1.5 injectos open at the same time. That is to say that the pump can flow 1.5 times what 1 injector can at the given pressure. Now as the second injector fires the pressure and volume flow through each injector decrease. This occurs for approximately 2ms. Now the second injector closes and the flow rate is immediately decreased. The dynamic pressure (V^2/2) will increase the static pressure very quickly back to the original static pressure and the fpr will vent off the extra fuel. what you end up with is a controlled fuel flow for 2ms followed by a decreased flow for each injector for 2ms. Your fuel pressure gauge may not be physically capable of showing a change this fast. Combine this with historesis effects and you can get a fuel pressure gauge that stagnates at the peak pressure reached during a cycle.

It can not be measured as a static system because the fuel in all parts of the system are not moving at the same velocity. I have also shown that you can be overrunning your pump during part of the cycle and not know it. The same is true for the FPR...Most FPRs are not capable of compensating for the dynamic part of pressure. Therefore you regulate the static part of the pressure and velocity changes can cause havoc on the system.

What you are talking about, if it was reality and not theory, would be a downside to any return line fuel system. Like I said, ok, so for 2ms, the fuel pressure is decreased by .000x psi, but it doesn't matter. Let's get a good thread going about something constructive that WILL make a difference on your motor.

 

[crankbender]

Obviously time isn't the same for me as it is for others.

I didn't come in here intending to tell anybody they were doing things wrong just wondering what had been done to correct these possible problems. I honestly was looking to get a few ideas here and possibly learn something. Yet once again this happens. Ok I will give people a chance to explain themselves before the readers of this post later on assumethe comments are stupid.

People have said that puddling doesn't occur. Ok prove to me how an injector that is open 90% of the time sprays into a valve that is open 36% of the time without puddling.

People have said that injectors arn't open at the same time. I have shown how this happens and proven that if you have a duty cycle over 75% then you HAVE to have all 4 injectors open at the same time....explain how you are able to keep this from happening in your particuar vehicle.

I have shown that you can have a varying fuel flow over very short periods of time. I have shown that your fuel consumption change can be as big as 100%. Some how this doesn't happen though. please explain this.

Once again somebody has said that math, physics, and reality don't mix. Please prove any law of physics wrong...If you do you will go down in history so you should really jump on this one.

I need to go now because people here on tuners are smarter than the likes of Newton, Bernoulli, and Einstein.

 

[Kevin Jewer]

I feel your pain Crank...

Here is how I see it. IIRC, the original discussion started about having a fuel pump smaller than the injectors. Which is what I have. At 80% IDC I should theoretically run out of fuel flow in my case (12.8:1, 43 psi base, 29 psi boost, .724 specific gravity, I ran through this exact example in several threads recently). Having injectors bigger than the pump doesnt seem to have done anything, since the wideband does indeed creep up from target boost AT 80.5% IDC, as seen on the datalog. The math works for me.

The larger injector will create a larger pressure drop sure (the original argument was that this is where a smaller-than-injctors pump will have trouble). But its for a shorter period of time. So it all works out in the end, and I still believe what I said in my original post:

I think its worth mentioning that if he is running 1600 injectors, but really only needs say 850s, then he only needs enough pump to "support" 850s. The pump has to be appropriate for the power goals, not the injector size.

I dont think we have to make it any more complicated than that, based on my findings with my setup.

 

[crankbender]

I feel your pain Crank...

Here is how I see it. IIRC, the original discussion started about having a fuel pump smaller than the injectors. Which is what I have. At 80% IDC I should theoretically run out of fuel flow in my case (12.8:1, 43 psi base, 29 psi boost, .724 specific gravity, I ran through this exact example in several threads recently). Having injectors bigger than the pump doesnt seem to have done anything, since the wideband does indeed creep up from target boost AT 80.5% IDC, as seen on the datalog. The math works for me.

The larger injector will create a larger pressure drop sure (the original argument was that this is where a smaller-than-injctors pump will have trouble). But its for a shorter period of time. So it all works out in the end, and I still believe what I said in my original post:



I dont think we have to make it any more complicated than that, based on my findings with my setup.

Although you could possibly make this work you will not have smooth fuel flow and pressure curves through your RPMs and pressures.

For instance imagine the person is designing for 800cc injectors at 70% IDC and buys a pump accordingly. At this point the most injectors he will have open at any 1 time is 3 (see above information). For some reason this person decides to get 1600cc injectors and puts those in the car.

Now theoretically if there are no flow problems he will have 35% IDC...with only 2 injectors open at any 1 time. However when he does have those 2 injectors open he will be wanting to flow 1.33 times the fuel that the 3 800cc injectors did. He needs a new pump to keep his curves smooth and avoid momentary lean conditions and poor fuel atomization.

Does this clear it up any on why you need to buy the pump for the flow and injectors and not just the max power?

 

[Kevin Jewer]

I dont see any evidence of this in my WBO2 trace, at 80% at least. Maybe in more extreme situations it would show up though.

 

[Mirage2LTurbo]

Maybe in more extreme situations it would show up though.

My point 10 posts ago.

 

[pneumo]

Hello, I lack the formal education you guys seem to have, so I'm not sure if this will be much of a contribution. And thank you Crankbender for explaining the big injector/small pump dillema in a way I understand.

Might there be some other mechanism that compensates for these minor fluctuations of pressure/volume? I ask this because a couple weeks ago I was playing around with a mechanics stethoscope and I noticed if I put it against the rubber fuel supply line before the rail I could hear the pulsations of the injectors opening and closing. Maybe the supply line acts as an elastic resevior that smoothes out the fuel supply?

Regarding fuel puddling; I'd like to offer a better definition of puddling. Anyone who has datalogged a stock DSM knows the injectors reach over 75% duty cycle during WOT, so fuel will be injected onto the backside of the intake valve. It even mentions it in the DSM tech manual. But is it really puddling? Maybe it would be best to describe it as a fine coating of fuel on the backside of the intake valve and surrounding port. Fuel can still become sufficiently atomized because the intake valve is hot, air velocity is highest in the port directly behind the valve, and there is enough turbulence through the port when the valve opens.

 

[Turbonium]

early injected systems relied on puddeling, . its not the best thing but it doesn't cause as much harm as it sounds. my 85 bmw has l-jettronic, which opens all 4 injectors at once but only provides 25% of the fuel needs of the motor, and although not the best system it works.
so what are the negative effects of soem slight puddeling?? i understand its less than ideal but i fail to see whta major problems it causes, and it it sounds to me like all of us at 75% duty cycle or greater are puddeling? thanks
Ryan

 

[blue1]

Guys this has been a great post every question and more has been answered! i would like to thank everyone for their posts but all remember if all goes well i only need the fuel flow for 11 or hopfully 10 seconds ! thanks again for all the input and hopefully i will be in the states in January so if you's have some good drag stuff coming up i will be there. Is there shit like what is on fast and furious happening that would blow my kids minds!! Would like to touch base with some DSM's when i'm there!!
Paul.