analyzing fuel injector flow

[someguy2800]

I've been reading up alittle on fuel injector size and nobody seams to have a good answer on fuel injector sizes for these cars. Some people say 42#/hr are good only for about 385 hp, others say they'll handle 500+. So you tell me, what aplication are you running (ie. turbo or supercharger, standalone or dme), what kind of power are you makeing, what boost pressure, and if you know it AFR and injector duty cycle. COME ON PEOPLE SPEEK UP! I WANNA HEAR IT! :alright

[highboostingm3]

Old setup:
GT30R
10.5:1CR
6-cyl s52 3.2L
13psi race fuel
425whp/477wtq Mustang Dyno
48lbers with room to make more power than that.

[Matt]

You are missing the most important factor you need to make a judgement about injector size.

Also, it's really annoying to have a one character thread title.

[highboostingm3]

You are missing the most important factor you need to make a judgement about injector size.

Also, it's really annoying to have a one character thread title.
You helped a lot by not stating the most important factor yet stating he missed the most important factor. Is this Jeopardy?

[Matt]

Kinda.

Fuel pressure?

[Julian]

You helped a lot by not stating the most important factor yet stating he missed the most important factor. Is this Jeopardy?

No thats just Matt

[highboostingm3]

Kinda.

Fuel pressure?
OMG you win! :wow

[bjl4776]

I dont wanna state the obvious but the engine makes a difference. If it is a 4 cylinder it has two less injectors than a 6. So if your talking to 4 cyl guys a 42lb injector won't make as much power as a 6 cylinder car. Maybe this is whats leading to your confusion, maybe not. Just thought id throw it out there

[someguy2800]

You are missing the most important factor you need to make a judgement about injector size.

Also, it's really annoying to have a one character thread title.


I acidently hit enter when I was changing the thread name.

And yes you could be talking about 40 psi or 4000 psi but allmost everyone here is on stock fuel pressure or very close to it, so its not really an issue. If you actually have information to add for once, I would like to hear it O fountain of all knowledge

[325icintn]

Can the mods change the title of a thread since the OP can't?

[someguy2800]

Old setup:
GT30R
10.5:1CR
6-cyl s52 3.2L
13psi race fuel
425whp/477wtq Mustang Dyno
48lbers with room to make more power than that.


By the way, thanks. Good info, just what I was looking for! :thumbup:

[MikeE36]

I've been reading up alittle on fuel injector size and nobody seams to have a good answer on fuel injector sizes for these cars. Some people say 42#/hr are good only for about 385 hp, others say they'll handle 500+. So you tell me, what aplication are you running (ie. turbo or supercharger, standalone or dme), what kind of power are you makeing, what boost pressure, and if you know it AFR and injector duty cycle. COME ON PEOPLE SPEEK UP! I WANNA HEAR IT! :alright


I believe card counter made 543 RWHP on 42#..

This is of course, with increased fuel pressure.. as Matt stated. This is definitely a big factor in being able to run that much power on 42's. Race fuel was used.

[someguy2800]

I believe card counter made 543 RWHP on 42#..

This is of course, with increased fuel pressure.. as Matt stated. This is definitely a big factor in being able to run that much power on 42's. Race fuel was used.

Do you meen his baseline fuel pressure, or his fuel pressure at full boost?

[95RogueM3]

Do you meen his baseline fuel pressure, or his fuel pressure at full boost?
Ulysses told me that his 543whp run was something of a glory-run on the 42# injectors and that he wouldnt run them that hard everyday. He DID say, however, that he ran them at 472whp for an extended period of time without ill effects (I believe that was at 3.5bar FP)

[danse]

Go to RC engineering's website and enter in your info: HP goals how many injectors and it will tell you what size you need for your goals.

[Matt]

How about 350 wheel on 19s on a 6 cylinder? Been done.

Fuel pressure is key. There is no use discussing injectors at all unless you discuss fuel pressure, unless you specify what car you're talking about. (e30s have 2.5 and 3 bar regulators, not sure about e36s)

[Robstah]

How about 350 wheel on 19s on a 6 cylinder? Been done.

Fuel pressure is key. There is no use discussing injectors at all unless you discuss fuel pressure, unless you specify what car you're talking about. (e30s have 2.5 and 3 bar regulators, not sure about e36s)

E36 stock fuel pressure is 3.5bar.

[someguy2800]

How about 350 wheel on 19s on a 6 cylinder? Been done.


Were not fucking talking about rising rate fuel pressure regulators. Add something we don't all know or go away.

[RRdawho?]

Well one aspect of fuel pressure is your fuel pump. Even if you have 550cc injectors, an E36 M3 fuel pump is pushing it around 320-350whp.

That being said I wouldn't use 42# injectors at stock fuel pressure at around 415whp on 91 octane. They go static.

I'm running 750cc's now. Go figure.

[nick4jc]

so guys.. even if u run a walbro 255lbs with 42# n a stock regulator its not going to help u push till 400wheels..????

regards,
Nick

[95RogueM3]

so guys.. even if u run a walbro 255lbs with 42# n a stock regulator its not going to help u push till 400wheels..????

regards,
Nick
It will as Nick G uses 42# injectors (and a Walbro 255) in his S2 kit and those routinely make 415+ whp at the stock FP.

[5mall5nail5]

They way I view it is, always overshoot your injector size by about 10%. So if you're looking to make 450 whp you should probably pick up some 48# or 55#, only because you don't want to be tuning your car at >80% DC. A lot of the calculators will churn out numbers based on a duty cycle of 70 - 75%, a lot of guys on here are probably running them 80-85%.

Fuel pressure is really irrelevant, as injectors are always rated at a specific fuel pressure, typically 3 - 3.5 bar. So, when you go look up Bosch 440cc (42#) injectors, it'll say 3 bar tested to flow 440cc's. If you run them at 3.5 bar, they're 48#, etc. The point is, you can only crank fuel pressure up so high. 350 whp on 19# injectors? What was that, 100 - 110 psi? I mean, really, that's not a good justification for fuel pressure.

Guys be aware that injectors are not typically rated much over 70 - 80 psi. You will pin the injector open or closed as the valve cannot function with such high pressure! And remember, its relative pressure, not base pressure, so when you take a factory 3.5 bar FPR with a 1:1 boost actuated diaphrame... 52 psi base pressure + 25 psi of boost puts it at 77 psi effectively... and that's getting quite high in terms of reliable operation and safety. You'll see people run stock 3.5 bar FPR with a 4:1 rising rate FPR, base pressure of 52 psi and 8 psi puts it over 80 psi fuel pressure...

Additionally, pressure is one thing... and then there's volume.... which is probably more an enemy

Then there's peak and hold.....


Another thing I forgot to mention is how AFR affects this. I ran 11.6 or so on the street, and retuned around 11.9:1, and I get like mid to high 60% DC.. like 68 or so, thats at 15 psi, from low to mid 70% DC.

[Matt]

Guys be aware that injectors are not typically rated much over 70 - 80 psi. You will pin the injector open or closed as the valve cannot function with such high pressure! And remember, its relative pressure, not base pressure, so when you take a factory 3.5 bar FPR with a 1:1 boost actuated diaphrame... 52 psi base pressure + 25 psi of boost puts it at 77 psi effectively... and that's getting quite high in terms of reliable operation and safety. You'll see people run stock 3.5 bar FPR with a 4:1 rising rate FPR, base pressure of 52 psi and 8 psi puts it over 80 psi fuel pressure...

I suggest you re-think this part.

What is the purpose of a 1:1 FPR? Why is it referenced to the manifold?

77psi into a manifold with 25psi of boost = equivalent to 52 psi of flow at atmospheric pressure in the manifold


Another way to think about it: If you have 2.5bar absolute pressure in the fuel rail and 2.5bar absolute pressure in the intake manifold, how much fuel is going to flow?

[Bav///Man]

Can the mods change the title of a thread since the OP can't?
Yes.

OP, what do you want the title to be?

[Matt]

Yes.

OP, what do you want the title to be?

"Add something we don't all know or go away."

[5mall5nail5]

I suggest you re-think this part.

What is the purpose of a 1:1 FPR? Why is it referenced to the manifold?

77psi into a manifold with 25psi of boost = equivalent to 52 psi of flow at atmospheric pressure in the manifold


Another way to think about it: If you have 2.5bar absolute pressure in the fuel rail and 2.5bar absolute pressure in the intake manifold, how much fuel is going to flow?


Sorry I got off track here at work - what I meant to say was that the x:1 RRFPRs will cause issues with over PSI of the fuel. 1 atmosphere of pressure in the manifold and say, 10 psi of positive manifold pressure on say a 6 or 12:1 FPR, would yield FP > MAP, by far, on either ratio. These are common FMU/RRFPR ratios, too.

Been doing this stupid script here at work and forgot where I was going with it - it happens - none the less, your forward pressure at the tip of the fuel injector, even though it might equal manifold pressure, is still going to be 70+ psi, and that is the issue... the valves cannot work under such high pressure. Yes you can argue that the pressure on the exiting side of the injector tip should == pressure behind the valve in the injector, but I don't have the time or desire to do the math involving surface area and valve speed, but basically I will draw the conclusion that it does not matter. Additionally, when people take fuel pressure into account, they forget to discuss injection style - bank, batch, sequential, semi sequential, etc. Take a fuel rail with 6 injectors on it and pulse 3 injectors at the same time, then do it with semi sequential 2 inj at the same time, and then sequential, your average fuel pressure will go down and down based on pulse. And, ultimately, this is where the tune comes in - pulsewidth, especially when talking about small injectors going high DC and P&H injectors. If you have a shorter PW, larger injector, you have more consistant FP regardless of what series you're firing the injectors in, as long as comparing both small and large injectors of same series firing. And so, bank firing a V6 with 55# injectors for 450 hp will have a more constant FP than bank firing a V6 with 450 hp with 36# injectors, simply because your PW will be shorter, your FP will not drop as low per injection, and etc., etc., etc. Again, there are two sides to this though involving lower engine speed/load minimum pulsewidth duration affecting idle (too big of injectors..) as well as impedance of injectors and effective injecto valve opening speed. And, typically, as you know, higher pressure usually means less actual flow up until a point, which is why we have injectors with bigger bores rather than just engineering 19# fuel injectors that can run at 800 psi. None the less, an RRFPR with a multiplicative pressure increase will over run your pressure ceiling and is unsafe.

[5mall5nail5]

"Add something we don't all know or go away."

Cut it out man

[Matt]

Sorry I got off track here at work - what I meant to say was that the x:1 RRFPRs will cause issues with over PSI of the fuel. 1 atmosphere of pressure in the manifold and say, 10 psi of positive manifold pressure on say a 6 or 12:1 FPR, would yield FP > MAP, by far, on either ratio. These are common FMU/RRFPR ratios, too.
Hate to sound like Mike here, but if that's what you meant to say, you should have said that.



Been doing this stupid script here at work and forgot where I was going with it - it happens - none the less, your forward pressure at the tip of the fuel injector, even though it might equal manifold pressure, is still going to be 70+ psi, and that is the issue... the valves cannot work under such high pressure. And, typically, as you know, higher pressure usually means less actual flow up until a point, which is why we have injectors with bigger bores rather than just engineering 19# fuel injectors that can run at 800 psi. None the less, an RRFPR with a multiplicative pressure increase will over run your pressure ceiling and is unsafe.

I assume the "we" I bolded is meant to mean the aftermarket, because when you look at GDI, you're basically talking about an injector running at a very high pressure, although I am not sure what the pressure differential is between the injector and the chamber at the time of injection.

I agree that there is a limit to how much fuel pressure can (or should) be run with traditional injectors, and I'm DEFINITELY not suggesting that a RRFPR is a good option for ANYONE. But... to discuss fuel injectors with no mention of pressure... :dunno


Cut it out man

Sorry, I just like to be treated with a bit more respect than that.

[5mall5nail5]

Hate to sound like Mike here, but if that's what you meant to say, you should have said that.
You? Sound like Mike? Never...

You know what I meant.




I agree that there is a limit to how much fuel pressure can (or should) be run with traditional injectors, and I'm DEFINITELY not suggesting that a RRFPR is a good option for ANYONE. But... to discuss fuel injectors with no mention of pressure... :dunno

Yeah but equally, if not more important, is volume. Nothing like spraying 5cc's of fuel at 150 psi I forget what formula to use (manning? i dont have anything here) but yeah theres an equal point of flow of small volume super high pressure and large volume super low pressure... as you know I am sure. Taking into account pressure is no more important than volume. Which brings us back to how all injectors are rated a certain flow @ given pressure. Most EFI injectors are going to assume at least 2.5 - 3.0 bar FP, so hp calculations are given at that fuel pressure (and in 1:1 it should remain unchanged, basically).




Sorry, I just like to be treated with a bit more respect than that.

Yeah but I don't think those sort of comments will gain it

[someguy2800]

Good info UM. You got me thinking, what do you think about putting an accumulator of some sort before the fuel rail? That should help level out the pressure as the injectors open on a batch fire injection system.

[5mall5nail5]

Good info UM. You got me thinking, what do you think about putting an accumulator of some sort before the fuel rail? That should help level out the pressure as the injectors open on a batch fire injection system.

Well we use alternating injection per engine cycle. So if the cylinder fire order is 1 5 2 4 3 6, the injectors batch 1 2 and 3 and 4 5 and 6 together and pulse the 3 alternating each other... the fuel pressure is really quite stable once you have an appropriate sized injector on there. Running small injectors at high pulsewidths is where you have issues, but the effect, even with small injectors, is very small.

[Matt]

You know what I meant.


It's not cool to post something wrong then say "you know what I meant" because there are a lot of people on here who don't know what you mean.

The formula is SQRT(new pressure/old pressure) * old flow = new flow

Most fuel injectors are rated at 3bar, so e36 users should multiply an injectors flow rating at 3bar by 1.08 to get the actual flow.

[5mall5nail5]

It's not cool to post something wrong then say "you know what I meant" because there are a lot of people on here who don't know what you mean.


:banghead:

[techno550]

Additionally, when people take fuel pressure into account, they forget to discuss injection style - bank, batch, sequential, semi sequential, etc. Take a fuel rail with 6 injectors on it and pulse 3 injectors at the same time, then do it with semi sequential 2 inj at the same time, and then sequential, your average fuel pressure will go down and down based on pulse. And, ultimately, this is where the tune comes in - pulsewidth, especially when talking about small injectors going high DC and P&H injectors.
Ideally, the fuel pump would have the capacity to keep up with the fuel pressure. the regulator is on the far side of the fuel rail for a reason. Fuel injection events should NOT cause any significant pressure drop in the line. Much less than 1psi.
You also left out the best fuel injection method. Sequential. You should fire one injector at a time. (or at least one cylinders worth of injectors at a time.) the timing of that injector's pulse is very important. You lose that control when you fire in a batch.



If you have a shorter PW, larger injector, you have more consistant FP regardless of what series you're firing the injectors in, as long as comparing both small and large injectors of same series firing. And so, bank firing a V6 with 55# injectors for 450 hp will have a more constant FP than bank firing a V6 with 450 hp with 36# injectors, simply because your PW will be shorter, your FP will not drop as low per injection, and etc., etc., etc.
A short but large injection pulse would be more difficult to stabilize than a long but small injection pulse. Even with multiple injectors.

[5mall5nail5]

A short but large injection pulse would be more difficult to stabilize than a long but small injection pulse. Even with multiple injectors.


...they forget to discuss injection style - bank, batch, sequential, semi sequential, etc.

I didn't forget sequential, I didn't use it in the example of worse to better in the example you quoted because its obvious

Not really, because you shouldn't be using 1600cc injectors to do a 2.0ms PW at highest load if you can use a 650cc and do 6ms... depending. So right, a gigantic huge pulse for short would shock the pressure of the fuel system, but you only run that risk when you need to. There are better alternatives at that point like staging. The whole concept is to optimize your fuel injector sizing relative to your hp, so if a big hit in fuel pressure is what it takes for you to flow enough fuel... do it, or use an alternative. Even batch/bank firing large injectors doesn't hurt the fuel pressure much at all.

[techno550]

I won't bother quoting because the important parts will be cut out anyway. :rolleyes

You have it backwards. Large pulses are always harder to stabilize than small ones.

Yes, the premise should always be to use the right size injector for the application. Not too large and not too small. How you fire them will have an effect on the quality, drivability, efficency, and overall power of the system.

[5mall5nail5]

Injection method may have affect on how the car drives and emissions but has no effect on ultimate power as long as it's setup properly. Carb and TBI cars make tons, and tons of power, oftentimes considerably more than the same motor converted to EFI. It's just not as nice to drive.


I won't bother quoting because the important parts will be cut out anyway. :rolleyes

You have it backwards. Large pulses are always harder to stabilize than small ones.

Mike before you start rolling your eyes, reread what I wrote. You missed what I was saying. Yes, if you have a 1' diameter pipe with 100 psi behind it and you hold it open for 1 second its going to drop pressure more than the same scenario held for 1 uSec. That's not my point. My point is, picking a 440cc injector and holding it open for 8 mSec and a then replacing it with a 550cc injector opening it for 5 mSec, might have the exact same effect on fuel pressure. However, there comes a point, and you can calculate it if you want, where the actual 1.x ms opening time is what affects your fuel pressure vs your actual PW duration - the fuel pressure regulator will work off of manifold pressure and so you should recover lost PSI, however a sudden large dump through a huge injector will hurt your rail pressure more so than a little baby opening that is held for longer. Because your motor is using the fuel you're holding a longer pulse width for, it's raising the fuel pressure, your average pressure in the fuel rail may be greater than the average fuel pressure of a whole bunch of 550cc opening times with less pulse width, so no larger pulse widths aren't "always" harder to stabilize. The injector is an opening, the bigger the opening, the more escape per instance, the more escape the bigger the pressure drop... which is why I am bringing to the table that more than the important of pressure, might be the importance of flow.

We can go back and forth about it all day, I just don't think you got what I was saying..

[techno550]

Injection method may have affect on how the car drives and emissions but has no effect on ultimate power as long as it's setup properly.
incorrect.


Carb and TBI cars make tons, and tons of power, oftentimes considerably more than the same motor converted to EFI. It's just not as nice to drive.
This is a misunderstanding of the hows and the whys.


Mike before you start rolling your eyes, reread what I wrote. You missed what I was saying.
I read it multiple times before I replied. I was trying to understand how you could get something so simple wrong.


Yes, if you have a 1' diameter pipe with 100 psi behind it and you hold it open for 1 second its going to drop pressure more than the same scenario held for 1 uSec. That's not my point.
If you want to use that analogy, it wouldn't be comparing a long pulse and a short pulse for the same size hole. its comparing the same duration pulse for a big hole or a small hole. The big hole will cause a larger pressure drop.


My point is, picking a 440cc injector and holding it open for 8 mSec and a then replacing it with a 550cc injector opening it for 5 mSec, might have the exact same effect on fuel pressure. However, there comes a point, and you can calculate it if you want, where the actual 1.x ms opening time is what affects your fuel pressure vs your actual PW duration - the fuel pressure regulator will work off of manifold pressure and so you should recover lost PSI, however a sudden large dump through a huge injector will hurt your rail pressure more so than a little baby opening that is held for longer.
So far this is correct. Oddly worded, but basically correct.


Because your motor is using the fuel you're holding a longer pulse width for, it's raising the fuel pressure, your average pressure in the fuel rail may be greater than the average fuel pressure of a whole bunch of 550cc opening times with less pulse width, so no larger pulse widths aren't "always" harder to stabilize. The injector is an opening, the bigger the opening, the more escape per instance, the more escape the bigger the pressure drop... which is why I am bringing to the table that more than the important of pressure, might be the importance of flow.
flow rate of an injector is quoted as a unit of volume over a unit of time. Pump capacity, likewise, is quoted as units of volume over units of time. The larger the injector flow, the closer you are to the capacity of the pump. This also means you are closer to exceeding the "replenishment rate" into the rail.

Large injectors also are more likely to have pulse harmonic issues in the rail. We'll refrain from in depth discussions of such events until we're past these *smaller* issues.


We can go back and forth about it all day, I just don't think you got what I was saying..
I understand what you are saying. You don't understand what I'm saying though. Its not just a question of understanding what is said... its a question of understanding the problem in general.

[5mall5nail5]

If you want to use that analogy, it wouldn't be comparing a long pulse and a short pulse for the same size hole. its comparing the same duration pulse for a big hole or a small hole. The big hole will cause a larger pressure drop.


In terms of an injector... why would you have a large injector and a small injector and use the same duration for pulsewidth - this would yield greatly different Air : Fuel ratio assuming air is constant (and we are). This is my fundamental point that I don't think you're getting. The same size hole will have the longer pulsewidth more difficult to maintain constant fuel rail pressure. But, why would I use the analogy of large vs small injectors and then tie it off with "the same size injectors"?

The big hole will cause more pressure drop only until a point, if the pulse is short enough the pressure drop will be less significant Delta P / Delta T, while a longer pulsewidth (to deliver the same fuel as the large injector...follow?) would have a greater Delta T but not necessarily a great Delta P, at some point if you graphed this, the lines would cross. And so, flipping a 4" butterfly valve open for 1/2 second might very well have a much greater change in pressure than a -3AN line with a solenoid held open for, say, 1 second, whilst both sources have equal pressure behind them. Additionally there is a sort of shock effect that occurs when large orifices relieve high pressure suddenly, effectively disrupting fuel flow within the fuel rail...


flow rate of an injector is quoted as a unit of volume over a unit of time. Pump capacity, likewise, is quoted as units of volume over units of time. The larger the injector flow, the closer you are to the capacity of the pump. This also means you are closer to exceeding the "replenishment rate" into the rail.

Yep I am aware, which is why I brought up to Matt that volume as being the primary component to injector horsepower rating while pressure is just a variable is conventionally your enemy as pressure can be manipulated easily [Post #22 2nd to last sentence]. That was the whole point of my bringing this up, thanks for ... confirming this?

[techno550]

In terms of an injector... why would you have a large injector and a small injector and use the same duration for pulsewidth. This is my fundamental point that I don't think you're getting. The same size hole will have the longer pulsewidth more difficult to maintain constant fuel rail pressure. But, why would I use the analogy of large vs small injectors and then tie it off with "the same size injectors"?

The big hole will cause more pressure drop only until a point, if the pulse is short enough the pressure drop will be less significant Delta P / Delta T, while a longer pulsewidth (to deliver the same fuel as the large injector...follow?) would have a greater Delta T but not necessarily a great Delta P, at some point if you graphed this, the lines would cross. And so, flipping a 4" butterfly valve open for 1/2 second might very well have a much great change in pressure than a -3AN line with a solenoid held open for, say, 1 second, whilst both sources have equal pressure behind them.

why are you still talking out your ass? that doesn't work on me.

I don't know why you thing a big but short pulse would have LESS of an effect on pressure in the rail than a smaller but longer pulse. (we can equalize the total fuel dispensed if you'd like.) Big pulse means big pressure drop.

Your "fundamental point" is fundamentally flawed.

I'd try to make this clearer with an ad absurdum example, but that would be misconstrued as usual.

To make this easier, why not restate the problem?

X psi fuel pressure in the rail at Y flow rate.
Z flow rate of injector size 1.
W flow rate of injector size 2.

Need to meter Q amount of fuel in a pulse.

That sound about right for a setup?
now show me some math...

[5mall5nail5]

why are you still talking out your ass? that doesn't work on me.

I don't know why you thing a big but short pulse would have LESS of an effect on pressure in the rail than a smaller but longer pulse. (we can equalize the total fuel dispensed if you'd like.) Big pulse means big pressure drop.

Your "fundamental point" is fundamentally flawed.

I'd try to make this clearer with an ad absurdum example, but that would be misconstrued as usual.

To make this easier, why not restate the problem?

X psi fuel pressure in the rail at Y flow rate.
Z flow rate of injector size 1.
W flow rate of injector size 2.

Need to meter Q amount of fuel in a pulse.

That sound about right for a setup?
now show me some math...

There is a point Mike where the brief drop in pressure of time will cross with duration of pressure loss over time. You know exactly what I am saying - a large injector will typically require shorter pulsewidth as a smaller injector to flow the same amount of fuel. The time between pulses is without pressure drop, thus your average fuel pressure in the rail will only be the same at the point where big injector pressure "dump" + remaining pulsewidth is equal to baby injector pressure "seep" + remaining pulsewidth are the same.

Buy a tank of gas - put a 4" valve on it, have another tank pump gas into that tank, flip the original open for a blink of the eye. Take the same tank of gas, same starting pressure, same fill tank rate, except have the valve 0.125" in diameter open for 2 seconds. Less violent of a pressure drop, much more easily replenished, no shock on the system if there were a second small valve, and if open for the right duration of time, you emit the same amount of gas as long as the next "cycle" doesn't require overlap with the longer pulse width. (This is assuming the replenishing source is flowing enough to handle the setup(s) )

[techno550]

There is a point Mike where the brief drop in pressure of time will cross with duration of pressure loss over time. You know exactly what I am saying -
:confused

let me see if I follow.


the brief drop in pressure of time
"drop of pressure in time". is that units of "drop in pressure" over units of "time"? or a drop in "pressure of time"?


duration of pressure loss over time.
duration of pressure loss = time of pressure loss


(time of pressure loss)
---------------------
time


cancel out time and we have "pressure loss".



There is a point Mike where the brief drop in pressure of time will cross with duration of pressure loss over time. You know exactly what I am saying -

so there is a point where "drop in pressure over time"?? equals pressure loss?
I can see pressure loss being equal to pressure loss. :dunno


I dunno if I follow. Then again its not like I have a degree in mathematics... no... wait... :shifty



a large injector will typically require shorter pulsewidth as a smaller injector to flow the same amount of fuel.
ok so far

The time between pulses is without pressure drop,
time during pulses could be witout pressure drop too. Depends on the fuel system and injector size...

thus your average fuel pressure in the rail will only be the same at the point where big injector pressure "dump" + remaining pulsewidth is equal to baby injector pressure "seep" + remaining pulsewidth are the same.
The pressure in the fuel rail should remain constant even during firing events. The times that its taxed are when there is a large draw, and that is what can result in a pressure drop.


Buy a tank of gas - put a 4" valve on it, have another tank pump gas into that tank, flip the original open for a blink of the eye. Take the same tank of gas, same starting pressure, same fill tank rate, except have the valve 0.125" in diameter open for 2 seconds. Less violent of a pressure drop, much more easily replenished, no shock on the system if there were a second small valve, and if open for the right duration of time, you emit the same amount of gas as long as the next "cycle" doesn't require overlap with the longer pulse width. (This is assuming the replenishing source is flowing enough to handle the setup(s) )

Lets try a better analogy.

We have two identical rivers. Both flowing X gph. We have people with buckets flinging water out of each river.
One river has 6 people each with a 5 gallon bucket. They take turns throwing out one bucket, once per minute.
The other river has 6 people with 50 gallon drums. They all dump throw their buckets at the same time once per hour.

in one hour, the 5 gallon bucket people have emptied 60x5=300 gallons.
in that same hour, the 50 gallon drum people have emptied 50x6=300 gallons.

which one was more likely to change the level of the river at the moment of throwing? Does the X gph come into play with the potential level change in the river?

[5mall5nail5]

We have two identical rivers. Both flowing X gph. We have people with buckets flinging water out of each river.
One river has 6 people each with a 5 gallon bucket. They take turns throwing out one bucket, once per minute.
The other river has 6 people with 50 gallon drums. They all dump throw their buckets at the same time once per hour.


:confused

Define dump throw, does dump throw = throw / dump???

...


You're saying the exact same thing I am, with different nouns.


If two rivers converge in italy, and one river has zebras in it, does the other.......




To the OP, since this is just turning into geography, general rule of thumb is 42# injectors == ~400 hp, 36 == 350 hp, 30 == 300, and so on. If you are wanting more than 400 hp but under 500 hp, I recommend oversizing the injectors moderately - you'd be good with some 55 - 65 # injectors with plenty of head room.

[techno550]

You're saying the exact same thing I am, with different nouns.

read it again. all of it.
you say there is a pressure drop with an injector pulse in the rail... and that its SMALLER with BIGGER injectors. The long pulse is easier to control than the short one, because the magnitude is smaller.

More importantly, how the injectors are fired makes a massive difference. firing two 300cc/min injectors at the same time is extremely similar to firing one 600cc/min injector. you get a bunch of 42's all firing at the same time and you'll run into odd problems much earlier than if you fired them sequentially.

[325icintn]

time during pulses could be witout pressure drop too. Depends on the fuel system and injector size...

That about summed it up for me.

[5mall5nail5]

That about summed it up for me.

Yeah he just repeated what I said in post #37,


Because your motor is using the fuel you're holding a longer pulse width for, it's raising the fuel pressure, your average pressure in the fuel rail may be greater than the average fuel pressure of a whole bunch of 550cc opening times with less pulse width, so no larger pulse widths aren't "always" harder to stabilize.

Maybe I am using a different browser or something.

[techno550]

ok, I guess I'll have pick this one apart too. :rolleyes

Because your motor is using the fuel you're holding a longer pulse width for, it's raising the fuel pressure, your average pressure in the fuel rail may be greater than the average fuel pressure of a whole bunch of 550cc opening times with less pulse width, so no larger pulse widths aren't "always" harder to stabilize.

The motor doesn't raise or lower the fuel pressure. it holds it constant with respect to the manifold pressure reference. If your base fuel pressure is 3.50 bar, your fuel rail to intake manifold differential pressure should be 3.50 bar. injectors firing or not.
It does this by *clamping* the return line at the opposite end of the fuel rail from the feed.

The fuel pump *should* be able to provide significantly more flow and pressure than the fuel injectors can consume. As the injectors use this flow, less is returned to the fuel tank.

The size of the injector (as well as how many are fired at the same time) is what dictates the potential for pressure drop, as well as the potential magnitude of the drop. Spreading the fuel delivery over more time always reduces the propensity for a pressure drop as it is less demand for flow.

There is no case where a larger injector would be less likely to cause a pressure drop in the fuel rail than a smaller one.

[325icintn]

Yeah he just repeated what I said in post #37,
...


Maybe I am using a different browser or something.I didn't read it all. Usually don't when you two get going.

I doubt the problem is the software. Probably PICNIC, i.e. user input. :D
http://consortiumlibrary.org/staff/gibbs/jokes/ComputerTechnologyToilet.jpg

[antonch]

If your injectors are having an affect on fuel pressure then you probably need a bigger fuel rail.

[techno550]

If your injectors are having an affect on fuel pressure then you probably need a bigger fuel rail.

Fuel pressure fluctuations can definately mean that. Though usually when you need a bigger rail, you also need a bigger line and bigger pump.

The other common issue is resonance in the fuel rail. a well placed pulse damper can fix that.

The other fix is to re-evaluate your injector size, and look at your injection method too. Run sequential when you can.

[5mall5nail5]

Fuel pressure fluctuations can definately mean that. Though usually when you need a bigger rail, you also need a bigger line and bigger pump.

The other common issue is resonance in the fuel rail. a well placed pulse damper can fix that.

The other fix is to re-evaluate your injector size, and look at your injection method too. Run sequential when you can.

Pulse shock / resonant effects were mentioned in post #35 The whole concept of greater volume is what I've been saying this whole thread.

[techno550]

Pulse shock / resonant effects were mentioned in post #35 The whole concept of greater volume is what I've been saying this whole thread.

oh? :rolleyes

I read it again and didn't see anything about resonance.


So right, a gigantic huge pulse for short would shock the pressure of the fuel system, but you only run that risk when you need to.
I'm not sure if shock is the right term, but close enough. The concept is that if your demand exceeds your supply, you run out. The key is that demand is injector size x number of injectors firing together.

for resonance, its placement that matters.


There are better alternatives at that point like staging. The whole concept is to optimize your fuel injector sizing relative to your hp, so if a big hit in fuel pressure is what it takes for you to flow enough fuel... do it, or use an alternative. Even batch/bank firing large injectors doesn't hurt the fuel pressure much at all.
batch/bank firing large injectors will cross the "don't cross this" line well before firing those same injectors sequentially. Batch firing is also is more likely to cause harmonic issues in the fuel rail as well as inconsistent pressure to the multiple injectors.

[5mall5nail5]

oh? :rolleyes

I read it again and didn't see anything about resonance.


I'm not sure if shock is the right term, but close enough. The concept is that if your demand exceeds your supply, you run out. The key is that demand is injector size x number of injectors firing together.

for resonance, its placement that matters.


batch/bank firing large injectors will cross the "don't cross this" line well before firing those same injectors sequentially. Batch firing is also is more likely to cause harmonic issues in the fuel rail as well as inconsistent pressure to the multiple injectors.

lol are you replying to the thread backwards?

[someguy2800]

I like this! When you two fight, we all learn something! One thing you guys didn't mention is that usually larger injectors don't atomize as well as small ones, and with such a short pulse width at low engine loads, it becomes kind of a bitch to get it to run well at idle or low engine loads. This is just what I've learned from forced induction drag V8's running over 100# injectors, but the one I've worked on run like shit at idle anyway. Mabey it isn't a big deal on these cars?

[ParadigmGuy]

I like this! When you two fight, we all learn something! One thing you guys didn't mention is that usually larger injectors don't atomize as well as small ones, and with such a short pulse width at low engine loads, it becomes kind of a bitch to get it to run well at idle or low engine loads. This is just what I've learned from forced induction drag V8's running over 100# injectors, but the one I've worked on run like shit at idle anyway. Mabey it isn't a big deal on these cars?
It's not a big deal unless you go very large. I run 75 lb injectors without having an idle problem.

[morerevsm3]

http://i5.photobucket.com/albums/y171/morerevsm3/funny%20pics/still-retarded.jpg
http://i5.photobucket.com/albums/y171/morerevsm3/funny%20pics/notthisagain0cj.jpg

[antonch]

It's not a big deal unless you go very large. I run 75 lb injectors without having an idle problem.

What injectors would those be? And are you running them fully sequentially?

[5mall5nail5]

What injectors would those be? And are you running them fully sequentially?

Just a guess but probably low ohm siemens injectors with resistors in sequential

[ParadigmGuy]

What injectors would those be? And are you running them fully sequentially?
They're Precision Turbo injectors and I don't think that my set-up is true sequential.

[5mall5nail5]

They're Precision Turbo injectors and I don't think that my set-up is true sequential.

ahhh man precision, damnit! siemens was a good guess tho!

Do you guys sell Precision turbos? Big ones?

[ParadigmGuy]

ahhh man precision, damnit! siemens was a good guess tho!

Do you guys sell Precision turbos? Big ones?
Yep.