Advertized injector flow rating ?

[Sleeper]

It's winter here, the car is in hibernation, and it's time to stir up the old grey matter.
I'm trying to understand manufacture injector flow ratings.
I'm looking for formulas and standards.

I have this one:

If I take the injector size and multiply that times the square root of (the applied fp divided by the test rating fp) I get the actual pph rating of the injector.

So if I use the stock injector @ 42psi
28Lb/hr x Sq Rt(42/43.51) =27.51pph

How does the duty cycle come into play formula wise? Is it at static or is 85% used as a standard.

I also understand that gas gives higher flow #'s than test solvent. Is there a specific gravity constant that can be plugged in to convert from gas to solvent, or visa versa?

The reason I ask is... I am running 52 lb low imp Siemens/Deka injectors, and after doing some reading I found out that they are called "Mopar Performance Super 60+40%" injectors and are rated at 52 lbs/Hr@55psi (???)
Pt# P5249452 or P4532586

52 x Sq Rt (42/55) = 45.44pph
52 x Sq Rt (45/55) = 47.0 pph
I can't seem find any more spec on them, and am not sure how the test DC comes into play.
(Are these actually smaller than MSD 50's?)


Thanks
Paul

 

[bruce]

The issue with injectors is that there is no Industry Standard for testing, and rating them, at least that I've seen posted.

The type of flow test media, and temperature, can make a marked difference in reported ratings.

 

[2QUIK6]

I think the general rule of thumb is 90% DC flow rate but I forget at what psi.

 

[Sleeper]

Bruce
From what I have found so far, most follow a standard of 3 bar (43.51psi) test pressure, except for some of the Chrysler and Porsche injectors, that use 3.7 bar or 55 psi. And a few at 2.5 Bar/36.25 P.S.I.
Again most test at 100% duty cycle, but after doing an archive search here I found this:
http://www.turbobuick.com/forums/showthread.php?s=&threadid=97964&highlight=siemens

quote:
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Originally posted by billsgn
Are you sure your 50# injectors only flowed 42-43#'s??? Some shops will flow rate injectors at only 80-85% which would make those injectors 49-51#'s I got my 50# injectors from PTE and they (PTE) flow at 85%.
--------------------------------------------------------------------------------

YES! you are absolutely right about any of the 50# Delphi/MSD type Injectors sold by PTE.

The Injectors are marked with the flow rating at the lower duty cycle........so they can be placed in bins and sorted as flow matched sets.

Flowing injectors at static/wide open is not the way to match Injector sets.

As stated most all 50#'s will flow about 48+ to 51 at 43.5#psi of fuel pressure. at 100% D.C.

Joe
PTE

Paul

 

[bruce]

Originally posted by Sleeper
Bruce
From what I have found so far, most follow a standard of 3 bar (43.51psi) test pressure, except for some of the Chrysler and Porsche injectors, that use 3.7 bar or 55 psi. And a few at 2.5 Bar/36.25 P.S.I.
Again most test at 100% duty cycle, but after doing an archive search here I found this:

It's not a standard if everyone's not using it. While you might use a particular pressure, there are still the issues about about what test media, and temp..

There are all sorts of suggestions about actual injector sizing, and DCs. I still maintain, no one's put the time into this area, as GM. If you want to double the HP of a given engine, then double the injector size, that GM supplied. That allows for proper AE tuning, and BL *logic* functioning. Full race setups, can fudge on sizing. But, the tuning with static injectors, isn't the way to do it, IMO. Reading up on abnormal combustion, will make you a believer.

 

[Sleeper]

From all that I have read so far, I agree with you.
N-heptane is commonly used, with a specific gravity of .688
Stoddard solvent is .772
Pump gas falls into the .68-.74 SG range
That still leaves a bunch of unknown others.
I can't seem find any definitive info on test temperatures.

We can cull the injector herd somewhat, by staying with common use, TR specific injector manufactures. Generally they seem to be grouped into:
Rochester/MSD/Multec/Delphi/Lucas,
Siemens/Deka/Motron.
Ford, Bosch/Accel are on the list, but used to a lesser extent.
I'm hoping that at least this grouping will narrow down the test variables somewhat.

Again generalizing here ... It seems that the flow rating may conveniently be inflated by some manufacturers depending on the static or dynamic (pulsed) test figures used, as well as the test psi. I know the media type and test temp play a major role in this but, as long as they specify the major test specs (Psi, DC) for the injector, we can get a "little bit" closer in leveling the playing field.

Paul

 

[Sleeper]

Getting back to my original thought...
Is it better to run these injectors at their rated psi ?

Paul

 

[bruce]

Originally posted by Sleeper
Getting back to my original thought...
Is it better to run these injectors at their rated psi ?

From what I've seen, and tinkered with, it takes 60s to get to where you have enough PW / DC to actually have control over your AFR, and a reasonable DC. Lots will argue that you can run static injectors, and get by with doing that, but, IMO, that always leaves you with poor to terrible AE.

IMO, it's best to run injectors at there stated spec. PSI, which is not because of the injectors, but because of the fuel pump.

 

[ThikStik]

Sleeper,
Off topic here, but are the back seats in the old Celica better than, the late Camaro's. There is one in great shape sitting up near here and Im jonesing for it.
Thanks

 

[Sleeper]

Originally posted by ThikStik
Sleeper,
Off topic here, but are the back seats in the old Celica better than, the late Camaro's. There is one in great shape sitting up near here and Im jonesing for it.
Thanks

??? I have know idea what the Camaro's look like.

Paul

 

[ThikStik]

The CamBirds have horrible little torture pits for seats. Worst thing is no leg room. I think the C has better seating which is wild as it is smaller..

 

[Sleeper]

Originally posted by bruce
From what I've seen, and tinkered with, it takes 60s to get to where you have enough PW / DC to actually have control over your AFR, and a reasonable DC. Lots will argue that you can run static injectors, and get by with doing that, but, IMO, that always leaves you with poor to terrible AE.

IMO, it's best to run injectors at there stated spec. PSI, which is not because of the injectors, but because of the fuel pump.

I jumped up a while ago from Blue Tops to the Siemens, because at the time, I thought they were slightly larger than 50's, and at that time, they were the smallest low imp inj you could get. Because of the " large" size, I wanted the quicker reaction times of the P&H's, so I would be able to better control the PW at low rpms.

I'm not sure I follow your above statement Bruce. Why "because of the fuel pump?"

Speaking of pumps... If I set the base FP to the 55 psi stated spec, and run 24 +/- psi of boost, I will be asking the pump to push 79 psi. Will a wired Walbro 340 be able to supply the required volume at that psi?


Paul
Paul

 

[bruce]

Originally posted by Sleeper
I jumped up a while ago from Blue Tops to the Siemens, because at the time, I thought they were slightly larger than 50's, and at that time, they were the smallest low imp inj you could get. Because of the " large" size, I wanted the quicker reaction times of the P&H's, so I would be able to better control the PW at low rpms.

I'm not sure I follow your above statement Bruce. Why "because of the fuel pump?"

Speaking of pumps... If I set the base FP to the 55 psi stated spec, and run 24 +/- psi of boost, I will be asking the pump to push 79 psi. Will a wired Walbro 340 be able to supply the required volume at that psi?

It's about design, as well as general characteristics. I've run my 60 PPH injectors on my TR using the Syclone ecm, ie Batch fire. To they'll work at very short PWs.

A fuel pump can do only so much work. If you crank the pressure up, then the AMOUNT of fuel the pump can pump at the higher pressure, will drop.

I run 42 PSI, 60's, and a double pumper. Engines, IMO, are just to expensive to waste due to being lean, even ocassionally, or just marginally.

 

[87GN_70GS]

Roughly, DC relates directly (linearly, but not exactly) to flow rate. At 50% DC, the injector is on equally as much as it is off, neglecting stuff like delays in current rise/decay due to solenoid winding inductance, saturation, voltage rise time, rpm, etc. So, at 50% DC, a 40 lb injector will flow roughly 20lbs/hr (40 x 0.50), all other things being equal.

 

[Ormand]

Yeah, what Bruce said, the pump is the problem. Suppose you run the injectors at 55 psi, hose off (no boost), then you try to run up 25 or 30 lbs boost, with alky, or with race gas. That makes the pump fight against 80 to 85 psi, plus line losses. Even with a Walbro 340, you will be so far out on the pump curve that you may suffer from not enough fuel. So you would have to have dual pumps, as Bruce mentioned, to provide any margin of safety at all. If you ran the injectors at less rressure, you won't get full rated flow, but that's a different problem. Just watch the knock sensor.

 

[Sleeper]

I guess a lot also depends on the RPM and PW commanded by the ECM. If at 5100 rpm I'm sitting in the 80 +/- 2% DC range at the 45 psi FP, upping the FP would lower the DC. Wouldn't the delivered volume be the same?

BTW Does anybody know what the Walbro specs are off hand?

80-85% DC seems to be the desired inj operating window. Are there problems caused by operating at a lower DC? Keep in mind that we are talking about Low imp P&H's.

Paul

 

[bruce]

Originally posted by Sleeper
I guess a lot also depends on the RPM and PW commanded by the ECM. If at 5100 rpm I'm sitting in the 80 +/- 2% DC range at the 45 psi FP, upping the FP would lower the DC. Wouldn't the delivered volume be the same?

BTW Does anybody know what the Walbro specs are off hand?

80-85% DC seems to be the desired inj operating window. Are there problems caused by operating at a lower DC? Keep in mind that we are talking about Low imp P&H's.

When discussing DC, knowing the RPM range of operation gets to be an issue, since it's then about time off that matters. So while 85% is a normal, if your running at really high you still could run into issues. Just to use some easy numbers, 80% DC at 6K RPM is 2 msec off time, but at 12K rpm it's only 1 msec off time, and then you could get into problems.

If your at 45 PSI as compared to 42, your *within* spec, IMO. For the 3 PSI diference, and if you've got the AFR you want, I'd suggest leaving it alone, rather then hammering on the engine, to get the corrections. IMO, you have to balance all issues, when going for the *correct* tune.

But, again, you want to make sure you have enough pump capacity.

There were some Walbro flow charts on line at one time, googling might get them, if no one remembers the link.

The other issue, is at idle the min pulse width to give stable injector operation. While in the pre 60 injector days, the rule of thumb was 2 msec for saturated injectors, and 1 msec for R+H's. But, with the 60s they'll easily go sub 2's, and remain stable, as deminstrated by the fact they I've run them in my car in batch fire mode, with a 750 RPM idle.

 

[bruce]

Originally posted by Ormand
Just watch the knock sensor.

And reading the plugs, the Knock Sensor can be blind to pre-ignition.

 

[Sleeper]

Originally posted by bruce
When discussing DC, knowing the RPM range of operation gets to be an issue, since it's then about time off that matters. So while 85% is a normal, if your running at really high you still could run into issues. Just to use some easy numbers, 80% DC at 6K RPM is 2 msec off time, but at 12K rpm it's only 1 msec off time, and then you could get into problems.

If your at 45 PSI as compared to 42, your *within* spec, IMO. For the 3 PSI difference, and if you've got the AFR you want, I'd suggest leaving it alone, rather then hammering on the engine, to get the corrections. IMO, you have to balance all issues, when going for the *correct* tune.

But, again, you want to make sure you have enough pump capacity.

There were some Walbro flow charts on line at one time, googling might get them, if no one remembers the link.

The other issue, is at idle the min pulse width to give stable injector operation. While in the pre 60 injector days, the rule of thumb was 2 msec for saturated injectors, and 1 msec for R+H's. But, with the 60s they'll easily go sub 2's, and remain stable, as deminstrated by the fact they I've run them in my car in batch fire mode, with a 750 RPM idle.

(It's not the 42-45 3 lb diff I am concerened with. It is the 12.5 lb diff going from 42.5-55)

I had a look at some old DS files and saw my DC sat at around 80% @ 5200 Rpm with the FP at 45 psi, so I played with some figures and came up with an inj rating of 37.62 pph. If I upped the FP to 55 psi, I had to lower the DC to 72% to get the same pph rating. Would this cause a problem at idle PW wise, going lower than the 1-1.5ms reaction time of the P&H's?

Paul

 

[bruce]

Originally posted by Sleeper
(It's not the 42-45 3 lb diff I am concerened with. It is the 12.5 lb diff going from 42.5-55)

I had a look at some old DS files and saw my DC sat at around 80% @ 5200 Rpm with the FP at 45 psi, so I played with some figures and came up with an inj rating of 37.62 pph. If I upped the FP to 55 psi, I had to lower the DC to 72% to get the same pph rating. Would this cause a problem at idle PW wise, going lower than the 1-1.5ms reaction time of the P&H's?

Paul

I don't know where the 55 is your first mentioning came from.

If your at 80% at 45, there's no reason to change.

What are you calling reaction time?, the min suggested operating pulse width, for P+H's has been given as 1 msec..