Accel 24# injectors work?

[zr1assassin]

I got a Smokin deal on a set of (8) 24# Accel fuel injectors, will these work as secondaries on a stock engine without retuning? Plug n play like the 21#s?

[zr1assassin]

Anyone.....

[LGAFF]

No they will run way too rich...

[zr1assassin]

No they will run way too rich...

But will work with proper tuning?

[Karl]

But will work with proper tuning?

Yes.

I run the same injectors on my primary & secondaries.

[zr1assassin]

Yes.

I run the same injectors on my primary & secondaries.

Stock engine or bigger ci?

[LGAFF]

You will likely get a rich code.

[XfireZ51]

But will work with proper tuning?

The calibration needs to be modified to tell the ECM it has bigger injectors. That might be enough but likely it won’t be. U will at least need to run a before and after datalog to confirm. The Injector Bias will also need to be updated to the correct values. Otherwise who knows.
Finally, I’m not a proponent of mixed injectors. Use one or the other. The calibration doesn’t differentiate between 2 different value injectors. Its looking for one type injector, and will treat the other one as if....

[zr1assassin]

The calibration needs to be modified to tell the ECM it has bigger injectors. That might be enough but likely it won’t be. U will at least need to run a before and after datalog to confirm. The Injector Bias will also need to be updated to the correct values. Otherwise who knows.
Finally, I’m not a proponent of mixed injectors. Use one or the other. The calibration doesn’t differentiate between 2 different value injectors. Its looking for one type injector, and will treat the other one as if....

Well I know pete runs 24# for secondaries on his 391pkg. So you can mix/match, just didn't know if it was acceptable on a stock ci engine

[XfireZ51]

Well I know pete runs 24# for secondaries on his 391pkg. So you can mix/match, just didn't know if it was acceptable on a stock ci engine

I love Pete. He is a great, great friend. Doesn’t mean I agree w everything he does. And he and I have discussed this. You can “make it work” but I’d rather not.

[zr1assassin]

I love Pete. He is a great, great friend. Doesn’t mean I agree w everything he does. And he and I have discussed this. You can “make it work” but I’d rather not.

Understood, thank you

[Karl]

Stock engine or bigger ci?

Current package is an AutoMasters Snake Skinner 350 with ~475+ fwhp.

[Paul Workman]

I love Pete. He is a great, great friend. Doesn’t mean I agree w everything he does. And he and I have discussed this. You can “make it work” but I’d rather not.

The better answer might be "IT DEPENDS..." (No?)

Off the top of my head, imbalanced injector flow isn't an issue until the secondaries are switched ON in a stock calibration mode, yes? The net result would suddenly be the AF ratio would go RICH due to the sudden imbalance, and the ECM/O2s would struggle to maintain the set AF, no?

I would think in a SECONDARY DELETED calibration the balance issue would be just a matter of tweaking the pulse width (dwell) duration to optimize the NET fuel flow because both injectors are always ON. Unlike a SECONDARY DELETED calibration, the point at which the ECM crosses over to SECONDARY ON mode varies depending on rpm/throttle conditions: NO SET rpm or throttle % so injector dwell settings on a static cal table wouldn't work so well. Would the range of ECM adjustment be able to compensate/accommodate in CLOSED LOOP mode?

Of course, in WOT (OPEN LOOP) mode, exact balance would not matter. O2 input is not considered (and fueling comes from a separate open loop fueling table NO?)

Gotta run... more later perhaps!

[zr1assassin]

The better answer might be "IT DEPENDS..." (No?)

Off the top of my head, imbalanced injector flow isn't an issue until the secondaries are switched ON in a stock calibration mode, yes? The net result would suddenly be the AF ratio would go RICH due to the sudden imbalance, and the ECM/O2s would struggle to maintain the set AF, no?

I would think in a SECONDARY DELETED calibration the balance issue would be just a matter of tweaking the pulse width (dwell) duration to optimize the NET fuel flow because both injectors are always ON. Unlike a SECONDARY DELETED calibration, the point at which the ECM crosses over to SECONDARY ON mode varies depending on rpm/throttle conditions: NO SET rpm or throttle % so injector dwell settings on a static cal table wouldn't work so well. Would the range of ECM adjustment be able to compensate/accommodate in CLOSED LOOP mode?

Of course, in WOT (OPEN LOOP) mode, exact balance would not matter. O2 input is not considered (and fueling comes from a separate open loop fueling table NO?)

Gotta run... more later perhaps!

Very good Info! Thanks

[XfireZ51]

The better answer might be "IT DEPENDS..." (No?)

Off the top of my head, imbalanced injector flow isn't an issue until the secondaries are switched ON in a stock calibration mode, yes? The net result would suddenly be the AF ratio would go RICH due to the sudden imbalance, and the ECM/O2s would struggle to maintain the set AF, no?

I would think in a SECONDARY DELETED calibration the balance issue would be just a matter of tweaking the pulse width (dwell) duration to optimize the NET fuel flow because both injectors are always ON. Unlike a SECONDARY DELETED calibration, the point at which the ECM crosses over to SECONDARY ON mode varies depending on rpm/throttle conditions: NO SET rpm or throttle % so injector dwell settings on a static cal table wouldn't work so well. Would the range of ECM adjustment be able to compensate/accommodate in CLOSED LOOP mode?

Of course, in WOT (OPEN LOOP) mode, exact balance would not matter. O2 input is not considered (and fueling comes from a separate open loop fueling table NO?)

Gotta run... more later perhaps!

Paul,

There is only one constant in the calibration that defines for the ECM what size injector its working with. This is one of the factors that the ECM utilizes to calculate the pulsewidth for any particular condition. It doesn’t matter Closed Loop or Open Loop, the ECM always calcs PW. Fueling is always based on the VE table. All WOT FUELING utilizes a modifier applied to those VE tables. Nothing separate about it. Open Loop utilizes the same VE tables but not modifying fueling w the O2 sensor input.
If you read my comment, I said its obvious that Pete, as an example, “makes it work”. For the way I tune, and for the type of HP the 391 is generating, I would use 24# injectors for primary AND secondary ports.
Also if you assume the 391 is going to generate ~ 600+chp, then using the BSFC calc, 22+24# injectors supports 588chp with an 80% duty cycle. Using 24# all around would support 614chp @ 80% duty cycle. You have more headroom before the injectors go static with a still controllable PW for idle quality.

BTW, the cal uses a 22.8# for the injectors. If u r using ACCELS, for example, the fuel flow is actually less than 21# which exacerbates the injector headroom issue a bit further.

[Paul Workman]

Paul,

There is only one constant in the calibration that defines for the ECM what size injector its working with. This is one of the factors that the ECM utilizes to calculate the pulsewidth for any particular condition. It doesn’t matter Closed Loop or Open Loop, the ECM always calcs PW. Fueling is always based on the VE table. All WOT FUELING utilizes a modifier applied to those VE tables. Nothing separate about it. Open Loop utilizes the same VE tables but not modifying fueling w the O2 sensor input.

Thanks for the refresher, Dom. Always good to hear from a real ECM practitioner (above). But, you miss my point (no doubt b/c I flubbed the question). Help us neophytes by concentrating on the steak, and not the peas...

FOR THE SAKE OF DISCUSSION ONLY:

Say the SECONDARY injectors pass X2 or make it X3 the amount of fuel that the PRIMARY injectors do, OK?
Now, the SECONDARIES are called, and the ECM splits the PW - being built to control balanced injectors, no?

Now, what do you think will happen when the SECONDARIES are switched ON?

Back to real world...

Here's the follow-on question(s): STOCK SPT or SPT DELETED: If one intends to use unbalanced injectors, which cal is most likely to work best from an overall driveabilty perspective: the stock cal with active secondary port throttles (SPT), or SPT delete mod?

Is there a limit to the range between injector rating, and if so, what is it?

Again, focusing on the AFR demands across the performance spectrum, can you describe to what extent will the ZR-1 ECM 'hocus-pocus" accommodate splitting of the fuel (injector) rating?

Note: The devil is in the details (the 'hocus-pocus') as always. Wow! Talk about a VE modifier...is what an unbalanced secondary injector acts like, no?

[Pete]

Injector constant can remain.
We only idle with primaries, we can control when the secondaries injectors go on.
If the car is tuned for the bigger secondaries should not be an issue.
Just throwing on bigger secondaries with out tuning will run rich at WOT.

Pete

[XfireZ51]

As Pete says, you will need to tune for the secondary injectors coming on line.
The LT-5 calibration has 4 VE tables for operation w closed and open port throttles. If u have the Valet key set to off, only the closed throttle tables are used even all the way up to 7500rpm and 100kPa. Same goes for the SA tables.
Its like tuning for 2 separate motors, but the constants in the cal remain the same for either state of operation, ie injector flow.
With split injectors, and secondarys removed, u tune the Closed Throttle VE essentially for idle or whenever the throttle is below a particular % open as defined in the calibration. As in decel for example or trailing throttle sometimes. When the throttle position reaches a point where secondarys are energized as defined in the calibration, the ECM divides the PW by a value in the cal. In a stock cal that’s 51%. But that’s 51% of the calculated total PW using the injector constant. Also, the ECM doesn’t drive the secondary injectors separately. The secondarys take their control from the primary injectors. As far as the ECM is concerned, its managing one set of injectors. When the secondarys come on line, they will utilize the PW as calc’d by the ECM for the size injectors of the primarys, which will cause the secondarys to put out more fuel than ncessary. As Pete says, it’ll run rich because the same PW from a larger injector means more fuel than commanded. So the “work around” is modifying the Port Throttle OPEN VE tables to take into account the “error” in the PW.
In addition, the electrical characteristics of the injectors may be very different. Part of the PW calc done by the ECM includes the Injector Bias based on Voltage and when calculated PW is small. Think of it as Spark Advance. It takes x amount of time to open an injector. And that time is dependent on voltage supplied. Since voltage varies based on electrical load, the engineers needed to maintain precise fuel metering in all conditions for emissions and economy. With two different injectors, those opening times will be different so any PW calc by the ECM will be inaccurate. We’re talking msec. of course. However, at small PW, given that the bias is a constant for a particular voltage, the error can be a significant % of the overall calc.
Finally, as in a previous post, I would want more “headroom” in my injector duty cycle. With the ~21# injectors most of us use, you r nearing the edge of needing bigger injectors when it comes to a ported and cammed motor w stock displacement. Based on BSFC, STOCK INJECTORS support~540chp with an 80% duty cycle, which is considered safe for an injector. A 391 represents nearly a 13% increase in displacement.
So my question is why would u skimp on injector? Were it my motor, I would use at least all 24s for this reason alone depending on what the CHP expectations were.
Again, as Pete has so often demonstrated, he knows how to “make it work”. I would take a somewhat different approach. We all learn from each other.

[tpepmeie]

As Pete says, it’ll run rich because the same PW from a larger injector means more fuel than commanded. So the “work around” is modifying the Port Throttle OPEN VE tables to take into account the “error” in the PW.



That's not the way I would do it. I would instead modify the Secondary Inj PW scalar. Simplistically, if you are running 24 lb secondary, and 21 lb primaries, the correct value would be (21 / (21+24)) = .47.

[Paul Workman]

As Pete says, you will need to tune for the secondary injectors coming on line.
The LT-5 calibration has 4 VE tables for operation w closed and open port throttles. If u have the Valet key set to off, only the closed throttle tables are used even all the way up to 7500rpm and 100kPa. Same goes for the SA tables.
Its like tuning for 2 separate motors, but the constants in the cal remain the same for either state of operation, ie injector flow.
With split injectors, and secondarys removed, u tune the Closed Throttle VE essentially for idle or whenever the throttle is below a particular % open as defined in the calibration. As in decel for example or trailing throttle sometimes. When the throttle position reaches a point where secondarys are energized as defined in the calibration, the ECM divides the PW by a value in the cal. In a stock cal that’s 51%. But that’s 51% of the calculated total PW using the injector constant. Also, the ECM doesn’t drive the secondary injectors separately. The secondarys take their control from the primary injectors. As far as the ECM is concerned, its managing one set of injectors. When the secondarys come on line, they will utilize the PW as calc’d by the ECM for the size injectors of the primarys, which will cause the secondarys to put out more fuel than ncessary. As Pete says, it’ll run rich because the same PW from a larger injector means more fuel than commanded. So the “work around” is modifying the Port Throttle OPEN VE tables to take into account the “error” in the PW.
In addition, the electrical characteristics of the injectors may be very different. Part of the PW calc done by the ECM includes the Injector Bias based on Voltage and when calculated PW is small. Think of it as Spark Advance. It takes x amount of time to open an injector. And that time is dependent on voltage supplied. Since voltage varies based on electrical load, the engineers needed to maintain precise fuel metering in all conditions for emissions and economy. With two different injectors, those opening times will be different so any PW calc by the ECM will be inaccurate. We’re talking msec. of course. However, at small PW, given that the bias is a constant for a particular voltage, the error can be a significant % of the overall calc.
Finally, as in a previous post, I would want more “headroom” in my injector duty cycle. With the ~21# injectors most of us use, you r nearing the edge of needing bigger injectors when it comes to a ported and cammed motor w stock displacement. Based on BSFC, STOCK INJECTORS support~540chp with an 80% duty cycle, which is considered safe for an injector. A 391 represents nearly a 13% increase in displacement.
So my question is why would u skimp on injector? Were it my motor, I would use at least all 24s for this reason alone depending on what the CHP expectations were.
Again, as Pete has so often demonstrated, he knows how to “make it work”. I would take a somewhat different approach. We all learn from each other.

Thanks to you, Pete, and Tod. I ain't ready to break into tuning (just yet). But, the clarification regarding the separate VE tables was the missing piece of the puzzle. Now it is all making sense (I thnk) - from the 10,000 foot level at least!;)

[XfireZ51]

That's not the way I would do it. I would instead modify the Secondary Inj PW scalar. Simplistically, if you are running 24 lb secondary, and 21 lb primaries, the correct value would be (21 / (21+24)) = .47.

Todd,

I’m going to make this point for the purpose of helping educate others here. Your suggestion of changing the Secondary Injector Scalar (which may be a misnomer) is simply to get the same “effective” PW as u would using two 21# injectors. Am I correct?
I’ll bet you will still need to visit the VE tables.
Second question, would that not negate the purpose of the 24# injectors in supplying fuel to a larger displacement motor?
BTW, I say the Secondary Injector Scalar is somewhat of a misnomer because the ECM does not drive the secondary injectors. The primary injectors signal the secondarys in terms of PW while the ECM simply energizes the secondary injectors thru the secondary relays.

[tpepmeie]

Todd,

I’m going to make this point for the purpose of helping educate others here. Your suggestion of changing the Secondary Injector Scalar (which may be a misnomer) is simply to get the same “effective” PW as u would using two 21# injectors. Am I correct?

Yes, same fuel mass delivered per injection event.

Second question, would that not negate the purpose of the 24# injectors in supplying fuel to a larger displacement motor?

Well, you would have more headroom before the secondary injectors are static, but by that time the primaries would be static, so what's the point? What I was trying to articulate is that it is completely feasible to run mixed injectors without a major tear up to the calibration. If somebody happens to have a set of secondaries which are larger, then very easy to calibrate--1 byte!

BTW, I say the Secondary Injector Scalar is somewhat of a misnomer because the ECM does not drive the secondary injectors. The primary injectors signal the secondarys in terms of PW while the ECM simply energizes the secondary injectors thru the secondary relays.

The correct label for that constant is technically "secondary injector ON pulsewidth scalar" In other words, its a scalar which gets applied anytime the secondary injectors are ON (via the ECM activation of the secondary relays).

[XfireZ51]

Thank you for the clarification. I hope it helps others following this. Cheers.