24, 26, or 30 lb injectors w/ AFR165, FTI, performer?

[rockin_rick]

I'm trying to nail down what injectors to order tomorrow for my AFR165, FTI, and Performer setup. Most people use 24's, but I've seen a few use 30's. I'd like to keep it as small as possible to help with idle quality, but don't want the duty cycle to be too high on WOT. Accel makes some 26 lbs-hr injectors, maybe these would be ideal.

According to the formula to determine the injector size needed based on HP level, the 24's seem too small to maintain less than a safe 80% duty cycle. Assuming the engine can produce 350FWHP, has a bsfc of .5, and not to exceed 80% duty cycle, the injector required would be a 27.3 lbs-hr.

--------------------------
Injector = (HP x bsfc)/Nc

Nc = number of cylinders
Injector = lbs-hr rating of injector
Dc = duty cycle
bsfc = brake specific fuel consumption (fuel efficiency)

To produce 350HP, a 24 lbs-hr injector would be pushed to about 91%. I realize that it will work, but it's shorting the life of the injector and risking burning it out. Of course, this is all math, and not real world use.

Has anyone logged duty cycles with a tweecer (or similar) to find out what they are with any of these injector sizes?

Even if you haven't, what is your opinion?

Thanks,
Rick

 

[Killercanary]

I run 24's without a problem, I highly doubtm I'm anywhere near maxing them out. Now, I don't think they'd support any sort of forced induction, but they'll handle anything I do with the current combo.

 

[rockin_rick]

Killer - I'm going to stay NA 302. How's your idle quality? I guess that I should have also asked how much fuel pressure is also being run through your injectors (or anyone else responding).

Thanks,
Rick

 

[Killercanary]

Rick, my idle is great, but it did require a bump in idle speed to 850-900rpms. I am running 40lbs of FP with the line off (if memory serves me right), but I used my EEC Tuner to add fuel under WOT over 3500. I'm 7% richer from 3500-up, this was done with my EEC Tuner under the WOT_FUEL_MULTIPLIER settings

 

[red94fiveo]

Rick, my idle is great, but it did require a bump in idle speed to 850-900rpms. I am running 40lbs of FP with the line off (if memory serves me right), but I used my EEC Tuner to add fuel under WOT over 3500. I'm 7% richer from 3500-up, this was done with my EEC Tuner under the WOT_FUEL_MULTIPLIER settings

Paul - quick question for you. I am doing the AFR/FTI swap in a couple weeks and am thinking of buying a twEECer. Are you and other people for the most part willing to share your twEECer settings, or is that something you'd prefer to keep to yourself. This will probably factor into my decision on whether to buy one or not. I think I'll be able to learn the twEECer, but it be nice to have some other settings to work of and learn from.

 

[Rootus]

I share my TwEECer settings, as do most people. It's not secret . I didn't create my own calibration from stock, I started with one from someone else who has a similar combo.

I think the 24# injectors would be perfect. I ended up going with 30#, but they're way overkill. I barely get to 50% duty cycle on them at peak torque.

Dave

 

[mo_dingo]

I share my TwEECer settings, as do most people. It's not secret . I didn't create my own calibration from stock, I started with one from someone else who has a similar combo.

I think the 24# injectors would be perfect. I ended up going with 30#, but they're way overkill. I barely get to 50% duty cycle on them at peak torque.

Dave

Like he said, 30lb are overkill, but I think you will lengthen the life of your injectors by going w/ the 30's IMO.

At least you will be upgrading your injectors. You have the right idea.
Scott

 

[Killercanary]

I don't mind sharing my setting because I have VERY LITTLE done. Seriously, there is a TON more I can do, I just lack the time to try new settings. All I have changed is my idle speed, WOT_FUEL_MULTIPLIER, global spark advance (which is basically the same thing as manually advancing your distibutor to bump your timing), crank fuel pulsewdith (to help a minor hot start problem my car sometimes has), tip in and spark retard (to prevent massive timing being pulled between each gear change since I don't powershift), and I sometimes set my WOT voltage setting a little lower than what is normal (I do this at the track ONLY because if I did it on the street I run the risk of going into WOT mode while at cruising speed).

 

[Stangfreak95]

TTT

 

[final5-0]

I'm trying to nail down what injectors to order tomorrow for my AFR165, FTI, and Performer setup. Most people use 24's, but I've seen a few use 30's. I'd like to keep it as small as possible to help with idle quality, but don't want the duty cycle to be too high on WOT. Accel makes some 26 lbs-hr injectors, maybe these would be ideal.

According to the formula to determine the injector size needed based on HP level, the 24's seem too small to maintain less than a safe 80% duty cycle. Assuming the engine can produce 350FWHP, has a bsfc of .5, and not to exceed 80% duty cycle, the injector required would be a 27.3 lbs-hr.

--------------------------
Injector = (HP x bsfc)/Nc

Nc = number of cylinders
Injector = lbs-hr rating of injector
Dc = duty cycle
bsfc = brake specific fuel consumption (fuel efficiency)

To produce 350HP, a 24 lbs-hr injector would be pushed to about 91%. I realize that it will work, but it's shorting the life of the injector and risking burning it out. Of course, this is all math, and not real world use.

Has anyone logged duty cycles with a tweecer (or similar) to find out what they are with any of these injector sizes?

Even if you haven't, what is your opinion?

Thanks,
Rick

Rick

I am running 30's cause I came up with the same numbers you did when using the various formulas.

I talked to Ed C and others about inj size. When I told them I would be using a tuning device (Tweecer) and stock fuel pressure they thought the 30's would be the way to go with my combo.

Without the Tweecer I might have gone with the 24's. Then again I would have needed to get an afpr.

Later
Grady

 

[GTJake]

Huh...this has got me thinking on what I should get. I do have a tweecer. I always thought 30's were overkill on a H/C/I 302.

Jake

 

[final5-0]

Huh...this has got me thinking on what I should get. I do have a tweecer. I always thought 30's were overkill on a H/C/I 302.

Jake

Jake

You might go to ProM's site and plug in your numbers to the inj size formula and see what you come up with for your combo.

Later
Grady

 

[GTJake]

Jake

You might go to ProM's site and plug in your numbers to the inj size formula and see what you come up with for your combo.

Later
Grady

Well, my combo is going to look identical to yours except for the RPM.

Jake

 

[GTJake]

I think the 24# injectors would be perfect. I ended up going with 30#, but they're way overkill. I barely get to 50% duty cycle on them at peak torque.

Dave

Do you think that is part of the reason that you were running so rich?

Jake

 

[Rootus]

Do you think that is part of the reason that you were running so rich?

Jake

No, I don't think the injectors have much to do with it. I think I run rich because of the longtubes, and because my O2 sensors have over 100k miles on them. With properly a functioning O2 setup, the EEC should be able to tune any setup on its own, unless it's too far out of spec (say more than 25%). That's for N/A cars at least.

Dave

 

[rockin_rick]

I just realized that the formula I posted didn't account for the duty cycle. Here is the new formula:

Injector = ((HP x bsfc)/Nc)/Dc

Nc = number of cylinders
Injector = lbs-hr rating of injector
Dc = duty cycle
bsfc = brake specific fuel consumption (fuel efficiency)

**********

The bsfc is the big question mark in this equation. So let's take Dave's data (and assume 355 HP) and see what his bsfc calculates out to:

Rearrange formula:

bsfc = (Dc x Nc x injector)/HP
bsfc = (.5 x 8 x 30)/355
bsfc = .34

Hmmm, I though that a very effecient car was about .45 - .50. .34 seems way too low, especially if you are running rich. But then, the max duty cycle would be during WOT, and wouldn't be using the O2's. Perhaps the richness that Jake was talking about was not during WOT. Still, .34 sounds way too lean. Any ideas on this?

Dave, are you sure that you only got 50%? I know that you know what your talking about, and I'm sure that you're aware of tweecer's duty cycle logging error and have corrected for it. What do you estimate your HP to be? What is your fuel pressure set at?

I think that I'll go with the 24's and, if necessary, turn up the fuel pressure. This should also help with fuel atomization, which might help with idle quality, since I'll be going with long tubes. Might the 30 pounders be a contributing factor to poor idle w/ LT's? Perhaps a lower fuel pressure, with a smaller pulse width would create a lesser quality spray and atomization at idle. Anyone have any thoughts on this?

Thanks,
Rick

 

[Rootus]

Dave, are you sure that you only got 50%? I know that you know what your talking about, and I'm sure that you're aware of tweecer's duty cycle logging error and have corrected for it. What do you estimate your HP to be? What is your fuel pressure set at?

No, I forgot about the error when I posted that.

I'm pretty sure that running the injectors significantly under their ability is bad for them, the sweet spot is somewhere in the 80-90% range (IF, big IF, I remember correctly... it's too early in the morning for coherent thought... ).

Fuel pressure is set at 39 psi. I'm guessing horsepower at 350-360 bhp.

Dave

 

[final5-0]

I just realized that the formula I posted didn't account for the duty cycle. Here is the new formula:

Injector = ((HP x bsfc)/Nc)/Dc

Nc = number of cylinders
Injector = lbs-hr rating of injector
Dc = duty cycle
bsfc = brake specific fuel consumption (fuel efficiency)

**********

The bsfc is the big question mark in this equation. So let's take Dave's data (and assume 355 HP) and see what his bsfc calculates out to:

Rearrange formula:

bsfc = (Dc x Nc x injector)/HP
bsfc = (.5 x 8 x 30)/355
bsfc = .34

Hmmm, I though that a very effecient car was about .45 - .50. .34 seems way too low, especially if you are running rich. But then, the max duty cycle would be during WOT, and wouldn't be using the O2's. Perhaps the richness that Jake was talking about was not during WOT. Still, .34 sounds way too lean. Any ideas on this?

A good idea here would be, better safe than sorry.

Dave, are you sure that you only got 50%? I know that you know what your talking about, and I'm sure that you're aware of tweecer's duty cycle logging error and have corrected for it. What do you estimate your HP to be? What is your fuel pressure set at?

300 to the wheels is about 350 at the crank.

I think that I'll go with the 24's and, if necessary, turn up the fuel pressure. This should also help with fuel atomization, which might help with idle quality, since I'll be going with long tubes. Might the 30 pounders be a contributing factor to poor idle w/ LT's?

Because of the Tweecer I am using stock fpr & stock fuel pressure so I guess stock fuel atomization also.

The O2's being farther away from stock location, not the size of inj's is what causes some lt probs.

Perhaps a lower fuel pressure, with a smaller pulse width would create a lesser quality spray and atomization at idle. Anyone have any thoughts on this?

With Tweecer, EecTuner, you can make these adjustments as I have done. I usually idle at about 800 rpm with no surges, stalls, etc. I can put it down to about 744 rpm with a choppy (due to cam) but steady idle but at night the lights dim a bit.

I have no probs with my 30's and I KNOW I have plenty of fuel for now and later on based on my combo goals.

Again, without a tuner or chip I don't know if the 30's would work out so good at idle and low load conditions.

Later
Grady

 

[rockin_rick]

The O2's being farther away from stock location, not the size of inj's is what causes some lt probs.

I have a theory about the LT problems vs. injector size on a H/C/I NA 302. I not intending on just starting an arguement with everyone, but would like to discuss this issue, and possibly discover a more specific cause of this idle surging with LT's. Some people experience this, and some don't. Their must be some reason, or most likely, combination of reasons that causes this.


It's my understanding that longtubes cause 2 faults with the O2 sensor.

#1 is the cooling effect at idle. How does this effect readings?

#2 is the sensors distance from the head. This causes a richer than actual reading. This should be able to be accounted for entirely in a custom program. Is this correct?

Grady, you said before that "you've seen your O2's cool down slightly during a very long idle period while data logging realtime with your Tweecer." You can't actually log (nor does the ECU know) the specific temperature of the O2 sensor, can you? If not, what data was logged that made you believe that the sensor was cooling? Was it just the air-fuel ratio that the sensor was outputting?


Ok, this is my theory -

Both Dave and Grady have 30 lbs-hr injectors and have both noticed some surging with LT's. Others with LT's have not. I'm not sure what size injectors they have, but it seems that most others have 24's. At idle, the pulse width to the injector is very small. Given the same fuel pressure on the same setup, 30's have to have a smaller pulse width than 24's. An injector driven with a too small of a pulse width can cause the spray pattern to not fully develop, causing poor atomization. This would lead to poor combustion, and unburnt fuel left over. Then the O2's would register rich, and the ECU would try to lean out the mixture more by shortening the already too short pulse widths. Then the RPM's would start to drop, and the ECU would recognize this, and compensate.

Perhaps the oversized 30's cause too small of a pulse width at idle, and a rich condition. The 24's PW is wider, allowing better atomization, thus better idle. Of course, this is combined with the LT's cooling effect, causing problems.

Does this make sense, or have I missed something or assumed something that isn't true? What are everyones opinions?

I'm going to post a new topic asking about injector size, w/ LT's and see what turns up.

Thanks,
Rick