Injector Opening Times

[bruce]

Does anyone have any facts or data to prove that using a Ideal Gas Law, such as F.A.S.T. claims, does offer any better fueling than a BPC, or BPW calculation?, considering that the injector opening time, is just a fudge factor.

And just as a FWIW, once you include the rounding *errors* that occur from the various calculations, what really is the difference in the three?. Other then the type of table used for editing.

Just to eliminate the what's grown to be normal, *do you have a problem with F.A.S.T. replies, no I don't*, I'm just about asking guestions, and trying to see if it really does matter or not.

 

[JDEstill]

I'll probably hate myself for this, but I guess I'll bite.

First off, what exactly do you mean by a BPW or BPC calculation? Can't tell you the difference if we don't agree on what we are comparing.

I believe that any decent speed density setup is ultimately based on the gas law. A GM TPI speed density setup for example, would have the gas law in it somewhere. The "density" in speed density is determined via the gas law, unless they for some unexplained reason the code writer included a big table of air density vs. MAT and MAP.

A DFI6 is not such a beast by the way, since they took the whole "density" part out by having a table of PW vs. MAP and rpm.

And I believe that any ecm is going to have to deal with the occasional fudge factor, such as injector opening time, whether it is aftermarket or OEM. Something like that has nothing at all to do with the determination of the fuel required by the engine, it is totally a problem of converting that need into the appropriate signal required by the hardware.

John

 

[bruce]

I'll probably hate myself for this, but I guess I'll bite.

First off, what exactly do you mean by a BPW or BPC calculation? Can't tell you the difference if we don't agree on what we are comparing.

I believe that any decent speed density setup is ultimately based on the gas law. A GM TPI speed density setup for example, would have the gas law in it somewhere. The "density" in speed density is determined via the gas law, unless they for some unexplained reason the code writer included a big table of air density vs. MAT and MAP.

A DFI6 is not such a beast by the way, since they took the whole "density" part out by having a table of PW vs. MAP and rpm.

And I believe that any ecm is going to have to deal with the occasional fudge factor, such as injector opening time, whether it is aftermarket or OEM. Something like that has nothing at all to do with the determination of the fuel required by the engine, it is totally a problem of converting that need into the appropriate signal required by the hardware.

John

BPC is the calculations GM typically does in the TBI setups.
BPW is used in the none Ideal Gas Law fueling strategies.
Injector constant, is what's used in the Ideal Gas Law, as implimented by GM.

From the way I see the *VE table*, when you have to fudge any values, you're not truely using it as a VE table. VE is volumetric Effiecency, which is about how mudh actual air is making it's way past the intake valve. Not to mention that it seems like no one will publicly state what sort of VE numbers they've gotten off a dyno (using precise measuring, and claculations, as opposed to *just* a MAF).

At best all I can see being done is an approximation of what's going on, so as long as the *obvious* corrections are made, what is there really to claim about something being an Ideal Gas Calculation*?.

Not to mention the rounding off errors. Stack enough of them together, and then all the math gets a little shaky (as far as being *exact*).

 

[JDEstill]

Well, looking at the P4 document that's been floating around the web, I see that the BPW calculation in section 9.1 has the term MAP/T in it. Any time you see pressure/temperature, think to yourself "gas law", since P/T with a constant tossed in is equal to density.

As I understand it, the DFI 7 and FAST basically figure up fueling as a function of engine speed, air density, desired a/f ratio, VE (and constants such as CID, inj size, number of injectors, number of cylinders, etc.) Looking at that P4 document, I'm seeing pretty much the same things, so what's the difference?

As for exactness, I would consider the manual fudging done with the VE table and things like the injector opening time to be equivalent to the fudging that GM does with BLMs. It's just that one is done manually and the other is done automatically.

John

 

[bruce]

Well, looking at the P4 document that's been floating around the web, I see that the BPW calculation in section 9.1 has the term MAP/T in it. Any time you see pressure/temperature, think to yourself "gas law", since P/T with a constant tossed in is equal to density.

As I understand it, the DFI 7 and FAST basically figure up fueling as a function of engine speed, air density, desired a/f ratio, VE (and constants such as CID, inj size, number of injectors, number of cylinders, etc.) Looking at that P4 document, I'm seeing pretty much the same things, so what's the difference?

As for exactness, I would consider the manual fudging done with the VE table and things like the injector opening time to be equivalent to the fudging that GM does with BLMs. It's just that one is done manually and the other is done automatically.

John

Just a minor point, but the BPW in that document isn't used.

The TBIs don't use the any IAT/MAT in their calculations.
The port like in the P4 document uses a MAT, and it's used in the timing and fuel cals.

That's my guestion, what makes the claim even worth mentioning?.

The BL isn't a so much of a fudge as to allow for things out of GMs control. ie gas brewing differences, vehicle maintance, etc.. Thou, in the TBI applications, it does allow for the fact there is no MAT/IAT correction.

Not to mention that if they were trying to use the injector opening time, as something really meaningful, why isn't a 2D table, as a function of voltage.

 

[RickWI]

The only reason you may want to deviate from an injector opening time of 1 is to dial in the ability for finer tuning at idle and very low load conditions. It' basically resets the numeric range at these low load conditions. It's much finer tuning if your base VE values are in the upper 30's or low 40's than if they are in the 20's.

It's not a fudge it's a tuning tool.

 

[bruce]

It's not a fudge it's a tuning tool.

Unless it's based on a given piece of fixed data, ie injector characteristic (of a specific nature), IMO, it is a fudge.

VE is VE, weither at 20, or 100. If you move the table values, as a matter of convience, the it's not really a VE table.

 

[norbs]

Just be glad you can fudge the numbers to make the car run better, and not rely on a pre programmed value, locked in some "code".

 

[bruce]

Just be glad you can fudge the numbers to make the car run better, and not rely on a pre programmed value, locked in some "code".

If it takes fudging thou, it negates, the claim that it's a true VE table. If it's not a true VE table, then it really does't matter if it's an ideal gas calulation or not.

Until the aftermarkets release the actual source code, you'll just never know what all they're denying you the ability to edit, or don't even have.

 

[gewroo]

The ideal gas law has nothing to do with fuel. The "gas" refers to air not gasoline. It's a law that relates pressure, temperature and volume of an ideal gas (like air). It's used (along with volumetric efficiency) to estimate the mass air flow into an engine. From that point, it's compared to a desired air fuel ratio to generate a fuel flow parameter and further compared to the operating dynamics to generate a desired pulse width. Basic speed-density stuff... The reason the injector opening delay is a variable and not a constant is so tuners can allow for the opening time differences of all the different injectors used. Injectors are not perfect electro-mechanical actuators. It takes a little time for the injector's pintle to pull open and the fuel to start spraying. This is what the injector opening time is for.

To suggest that injector opening time has anything to do with the engine's volumetric efficiency or the ideal gas law is ridiculous. If you know the injector opening delay of a particular injector then it's a known quantity and not, as you say, "a fudge" even if the strategy allows for estimation. The same holds true for the VE table.

 

[bruce]

To suggest that injector opening time has anything to do with the engine's volumetric efficiency or the ideal gas law is ridiculous.

If you know the injector opening delay of a particular injector then it's a known quantity and not, as you say, "a fudge" even if the strategy allows for estimation. The same holds true for the VE table.

Where did I say that?.
If you want to just use estimates, then the VE table isn't really a VE table. If you're using it just to get the fueling correct, that's perfectly fine, but, if it's not a true VE table, then why the advertising claim?.

If you ignore the voltage compensation, then it's a very rough estimate. If your settling for estimates, or fudges, then again that brings us back to my original question:

Does anyone have any facts or data to prove that using a Ideal Gas Law, such as F.A.S.T. claims, does offer any better fueling than a BPC, or BPW calculation?, considering that the injector opening time, is just a fudge factor.

The point is, why

 

[gewroo]

Where did I say that?.
If you want to just use estimates, then the VE table isn't really a VE table. If you're using it just to get the fueling correct, that's perfectly fine, but, if it's not a true VE table, then why the advertising claim?.

An engine isn't a perfect air breathing machine so its efficiency becomes an important part of the air flow estimate. It's not easy to measure the VE but it's not too bad to estimate and with a wide band O2 sensor, it's fairly easy to check. Who said it wasn't a true VE table (besides you)? It certainly behaves like one.

If you ignore the voltage compensation, then it's a very rough estimate. If your settling for estimates, or fudges, then again that brings us back to my original question:

Does anyone have any facts or data to prove that using a Ideal Gas Law, such as F.A.S.T. claims, does offer any better fueling than a BPC, or BPW calculation?, considering that the injector opening time, is just a fudge factor.

It seems like you are implying that there is a voltage compensation component to the air flow calulation... The voltage compensation is to the fuel flow calculation.

You continue to imply that the injector opening time has something to do with the ideal gas law. It has nothing to do with it. The ideal gas law (with the VE table) is used to estimate the air flow and the injector opening time is used to compensate fuel delivery for the mechanical latency of the injector.

You ask questions like your claims are foregone conclusions. Don't be be too surprised if everyone doesn't buy into your hyperbole.

The point is, why

You should consider enrolling in this class: http://www.efi101.com.

BTW: What do you do with all those nits anyway?

 

[bruce]

An engine isn't a perfect air breathing machine so its efficiency becomes an important part of the air flow estimate. It's not easy to measure the VE but it's not too bad to estimate and with a wide band O2 sensor, it's fairly easy to check. Who said it wasn't a true VE table (besides you)? It certainly behaves like one.

It seems like you are implying that there is a voltage compensation component to the air flow calulation... The voltage compensation is to the fuel flow calculation.

You continue to imply that the injector opening time has something to do with the ideal gas law. It has nothing to do with it. The ideal gas law (with the VE table) is used to estimate the air flow and the injector opening time is used to compensate fuel delivery for the mechanical latency of the injector.

You ask questions like your claims are foregone conclusions. Don't be be too surprised if everyone doesn't buy into your hyperbole.

You should consider enrolling in this class: http://www.efi101.com.

BTW: What do you do with all those nits anyway?

What do you mean it's not easy to measure VE?, all it takes is a calibrated MAF, and some simple math. WB O2 while a great tuning tool, are just that, tuning tools, and subject to many inaccuracies.

Behaving like one, isn't the issue. If you have to estimate large and important entries, and fudge numbers to get the tables in a reasonable range, why bother calling it something, that it's not?.

That's not at all what I said. If they are using the injector opening time, as a critical element of the calculation, why don't they give you the option to use a voltage correction for the opening time, since voltage is what in large part dictates the opening time.

Again, you're doing a great job of assuming. I'm not asking anyone to buy into anything.

Excuse me for ignoring the drivel part of your response.

 

[gewroo]

What do you mean it's not easy to measure VE?, all it takes is a calibrated MAF, and some simple math. WB O2 while a great tuning tool, are just that, tuning tools, and subject to many inaccuracies.

Are we off the subject of speed-density now? If you used a MAF system, you wouldn't need to know the VE because you already know the important part... mass air flow. Are you suggesting that everyone who buys an aftermarket speed-density EFI system also needs to buy a "calibrated" MAF sensor to use with other instrumentation and complex math to formulate the VE? What controls fuel for the engine while your MAF measurement is taking place? Pardon me but I still think it easier (for probably everyone but you) to estimate the VE and calibrate with the O2.

You do know that "volumetric efficiency" is not actual air flow but is the ratio of inducted air volume vs. positive displacement, correct?

Behaving like one, isn't the issue. If you have to estimate large and important entries, and fudge numbers to get the tables in a reasonable range, why bother calling it something, that it's not?.

If you don't know the VE than you need to estimate. "Have to..fudge numbers"? Because someone may "fudge" a value for the sake of expediency, does not negate any description of function. Perhaps what you call a "fudge" is another, less perfect person's calibration. Are you now claiming that it's not a VE table???

That's not at all what I said. If they are using the injector opening time, as a critical element of the calculation, why don't they give you the option to use a voltage correction for the opening time, since voltage is what in large part dictates the opening time.

Who said it's "critical" to any calculation? It's an offset for the mechanical latency of an injector. Who said that voltage correction isn't already used to compensate the opening time? Why does voltage correction need to be an option? You say voltage is a "large part" of what dictates the opening time... What about the mass of the pintle? Inductance? Pressure differential? What about the closing time? How far do you want to go with this? They're all factors. Which ones can be "fudged" and which ones can't? Who decides? You?

Again, you're doing a great job of assuming. I'm not asking anyone to buy into anything.

Perhaps you're right. I'm assuming you say what you mean. Now I'm not even sure you know what you mean.

Excuse me for ignoring the drivel part of your response.

Drivel? Try comedy relief (It was a little funny).

Consider this: Aftermarket EFI systems are like any other commercial products.. They're full of compromises. Just deal with it.

 

[Joe Lubrant]

I was wondering where this thread was headed?

 

[gewroo]

You're right Joe... Same place as usual. Sorry, my bad. :frown:

 

[norbs]

Interesting point

 

[bruce]

Are we off the subject of speed-density now?

You really just can't put two and two together can you?.

You said:
**It's not easy to measure the VE but it's not too bad to estimate and with a wide band O2 sensor, it's fairly easy to check**.
To which I responded:
**What do you mean it's not easy to measure VE?, all it takes is a calibrated MAF, and some simple math. WB O2 while a great tuning tool, are just that, tuning tools, and subject to many inaccuracies.**

I wasn't talking about changing systems, I was responding to your past statement.

Again, your just playing some petty game instead of trying to contribute, thanks for nothing.

 

[bruce]

I was wondering where this thread was headed?

As a moderator, why don't you steer the thread, and remind people to try and stay on topic?, instead of post nonsense like you just did?.

 

[JDEstill]

Does anyone have any facts or data to prove that using a Ideal Gas Law, such as F.A.S.T. claims, does offer any better fueling than a BPC, or BPW calculation?

OK, OK, settle down...

I really don't have time to do any searching on this, so perhaps you can tell me Bruce, what are the steps involved in, say, the BPC or BPW calculation for a GM speed density ecm? 749, TPI, whatever. I'm betting the gas law is in their routine somewhere. It might not be obvious, but I bet it's there. So tell me how they figure up the inj pw to command. They do some kind of A x B x C x D = pw, so what are all the A, B, C, D, etc they use to get there? If that P4 document doesn't give the right equation like you say, then what is the right one?

John