my ecu was thinking it was a 750 cc injector which is why it says over 120%idcs. it thought that because i had to change injector size to compensate for e85.

flawlessTSI said:

after injectors are past 100% duty cycle it is then controlled by fuel pressure. thats why i raised my fuel pressure.

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Right, and raising fuel pressure should increase mass flow and bring the IDCs down.

So in your case.. you would have to raise your base pressure high enough to bring the IDCs back down to manufacturer recommend spec that you would be above the rated service pressures of any electric pump on the market with an appreciable amount of boost added on top

Not to mention you'd probably be surpassing the pumps flow capabilities, even with it juiced on a Boost-A-Pump.

Why is this so hard?

jrohner said:

So 120% of something IS possible. Wow, I totally got it now.

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Bravo sir. Those mental gymnastics required to stick to your pre-conceived notions and to not understand what is being explained would earn you a podium finish in most arenas.

IDC is a function of pulse width and RPM (or time actually), not injector size. Bigger injectors don't change time unless they make you go faster than the speed of light (which changes how fast time goes by).

LandSpeed-DSM said:

Bravo sir. Those mental gymnastics required to stick to your pre-conceived notions and to not understand what is being explained would earn you a podium finish in most arenas.

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I think you are the closed-minded one with your 80% set in stone that no one has posted any proof of. If you say something without proof, you can't call someone else out for asking for the proof.

LandSpeed-DSM said:

Right, and raising fuel pressure should increase mass flow and bring the IDCs down.

So in your case.. you would have to raise your base pressure high enough to bring the IDCs back down to manufacturer recommend spec that you would be above the rated service pressures of any electric pump on the market with an appreciable amount of boost added on top

Not to mention you'd probably be surpassing the pumps flow capabilities, even with it juiced on a Boost-A-Pump.

Why is this so hard?

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my pump was rated for a max of 80psi. with base pressure set to 50psi i still had 30psi left if i added 1psi of fuel per 1psi of boost. i knew this and i never ran more than 30psi.

flawlessTSI said:

my pump was rated for a max of 80psi. with base pressure set to 50psi i still had 30psi left if i added 1psi of fuel per 1psi of boost. i knew this and i never ran more than 30psi.

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Except do the math on what it would take for base pressure to put those injectors at 80-85% IDC max, provided you had enough fuel behind it at that pressure.

Now add 30psi boost.. and compare that combined pressure to your current pump's rated max.. or even say a very large, high pressure pump like my MP4303

If you want math for injector size, do it by converting AFRs and your airflow into actual fuel flow. It's not hard at all, and you can even multiply it by your all-important 80%.

jrohner said:

IDC is a function of pulse width and RPM (or time actually), not injector size. Bigger injectors don't change time unless they make you go faster than the speed of light (which changes how fast time goes by).



I think you are the closed-minded one with your 80% set in stone that no one has posted any proof of. If you say something without proof, you can't call someone else out for asking for the proof.

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Don't argue about it on the internet then. Go call the manufacturer, as I have stated a couple times now.

You are a true believer, and maybe just maybe talking to someone indisputably authoritative on the subject will get the idea behind the concept through that thick, willfully ignorant skull of yours.

Best of luck

LandSpeed-DSM said:

Don't argue about it on the internet then. Go call the manufacturer, as I have stated a couple times now.

You are a true believer, and maybe just maybe talking to someone indisputably authoritative on the subject will get the idea behind the concept through that thick, willfully ignorant skull of yours.

Best of luck

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YOUR first post mine seemed like the start of an argument.

So it's my job to prove your point as right? And now I'm ignorant for safely running more than your 80% for years -- there's my real world experience on the subject.

Also, I have not talked down on you or called you any names.

jrohner said:

So 120% of something IS possible. Wow, I totally got it now.

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It's theoretically possible... just not physically possible.

I totally agree that the displayed IDC should be capped at 100%.

Calan said:

It's theoretically possible... just not physically possible.

I totally agree that the displayed IDC should be capped at 100%.

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I disagree that in theory my 16 gallon gas tank can hold over 19 gallons. If you get over 100%, then the math is wrong, not theory.

what we have here is two people that have real world experience running over100% idc and a few people that are going off of what they read on the inerwebz... hmm.

jrohner said:

I disagree that in theory my 16 gallon gas tank can hold over 19 gallons. If you get over 100%, then the math is wrong, not theory.

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The math is not wrong, but instead just not capped at 100% (in this case, via ECMlink). I can show you a log that has over 100% as I've hit 124% in the past. The variables that go into the IDC calculation are read at whatever the ECU sees. But if you have a variable that allows the calculation to push above 100%, then it happens and shows in the software's UI.

(nm)

with the increased fuel pressure i also had full control of my injectors at 120+ idc.

Changing AFR's by changing fuel pressure isn't exactly what I would call control. If your injectors really are absolutely maxed (for real, not theoretically), then you would have no correction for changes of conditions which would be unsafe (if it got colder out, you would go lean).





My cousins Evo broke 100% IDC's (little 680's on E85 w/ 25psi of boost), and his AFR's were still where I expected them to be.

i still had control with link settings not just fp. if i ran in to the problem on no control change with link then i would of upgraded injectors .

I took it as though you increased FP to get your AFR's right but you must have meant that you increased FP to give a little more injector headroom. I always run stock FPRs, so I don't play with FP much other than swapping to different FPR's (2G, 1G turbo 5spd, 1G turbo auto, 1G NA, etc).

Okay so lets just teach you all about an injector. Since it sounds like there's not a lot a research has been done on them. http://docinjector.com/info1.htm

This too: http://injector-rehab.com/shop/idc.html

jrohner said:

And now I'm ignorant for safely running more than your 80% for years -- there's my real world experience on the subject.

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I'm not trying to single you out at all or get into what has turned into a debate that is really in all pointless... IMO.

But, the point that I was trying to make that seems to may have started this is.

Common sense tells us that above all We Don't want to tune to max. Regardless of whether it is the "real" limit or not because head way is what you want and a margin of error.

Hence the 80% as the manufacturer and "norm" standard that is accepted... .

If someone tunes there car on a hot summer day to 100% duty where is your headroom for error? On a Cold winter day when the air charge is denser and you may be flowing more air and making more power... ? Even if it's not truly 100% based of of any calculation??? As well there is not a context to what conditions you or anyone else "always" ran their injectors a x amount of duty.

I think I said earlier or might not IDK, I have at some point ... There is a big difference for an example. Of what someone drag racing for less then some 10-11 seconds. Pushing the injectors to what they accept as the Max Is going to want. The environments condition are not going to change in that short time. Compared Then what to someone running on a road course is going to see over X amount of time. There are so many factors that come into play that it just doesn't make sense. But that's just my opinion on it... .

I think that the only point that should be made. At least the main one that I was emphasizing is that tuning OVER 100% is not advisable, not that to Never go over 80% or something bad is going to happen... .

I think everyone forgets that there is an audience of sometimes misinformed people here that give out advice solely on what they read. whether in context or not. or in all consideration over waht Everyone might be saying.

That the main point is that it's not advisable and when saying you did something all the context of that should be stated.

When I first ran E85 I ran a set of 880's an tuned them to the max an ran like that for quite awhile... BUT I also keep a very keen eye on things and always adjusted to keep things in check. Would I recommend that to the next guy just cause I did, you did, and the next guy did... ? No

Another over look factor is that spray pattern people are ending up with. They can't see when jacking up their Base pressures for X injector... Some don't play as nice as the next

The key word is duty cycle. The injector is open the entire combustion cycle(intake, compression, combustion, exhaust) at 100% idc. Of course it can't be open for longer. I really don't think anyone is arguing that especially if they understand the concept. The ECU is requiring x% of the flow rate available. In our ECU's case is doesn't know any better and there is an interface error above 100%. The end result is the same; the injector gets a constant ground signal whether the ECU demands 101% or 125% "idc."

FWIW I would start with a basic 255 Walbro or some of the other higher flowing single in tank pumps that are now available. Every setup will be different but I didn't start to run out of pump until a good bit after 500whp(my dyno was at 30 psi, now at 35). An injector in the 1200ish range would be a decent option for the price before low speed drivability may start to come into play when you go larger than that on a standard injector. The 2150's etc are great but are a big price jump for a 500hp goal.

I'm not sure the exact reason 80% duty cycle was picked for a rule of thumb. The first possible reason has been stated well by other posters, such as my1gdsm, Calan, and landspeed-dsm. Fuel headroom during different operating conditions. The second and third are unclear to me on which may be more important; the injector heat over time, or the injector driver. Also stated by Calan. I would assume the injector driver will be more likely to fail similar to what happens when you run a low impedance injector on a high impedance driver without a resistor box. Eventually enough heat will build up to fry the driver since there are more amps being pulled(Ohms law, less resistance more amperage at the same voltage). It won't happen right away but if there is more heat being put into the driver than it can dissipate it will eventually fail. Duty cycle directly correlates to the % heat load put into the driver, no matter what size hole is at the end of it(Ohm's being constant between injectors). For cars that rarely see WOT for more than 10-15 seconds at a time I wouldn't think you would see a whole lot of injector or injector driver failures especially with the small sampling of people that have contributed to this thread. As others have stated, road racing may be a different story.

flawlessTSI said:

what we have here is two people that have real world experience running over100% idc and a few people that are going off of what they read on the inerwebz... hmm.

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How does that phrase about assuming go?

http://www.dsmtuners.com/forums/newbie-forum/422900-things-not-do-14b-450s-boost-turned-up.html

To add further to what MY1GSM and Mr Peepers were getting at ... you are also changing the range of the injection period when you have to keep it open that long.

Since we all have our math hats on tonight.. any one want to muse at the delta theta from having to keep the injector 20% longer, and what that does to the flame front propagation among other things?

Going back to one of my first posts in this silly debate, no one is pretending things are going to explode at 81% it's a margin for error.

Also, in an application like mine where you 're WOT for 5+ miles it's a big deal

LandSpeed-DSM said:

Going back to one of my first posts in this silly debate, no one is pretending things are going to explode at 81% it's a margin for error.

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That's actually the exact reason an argument started is because a couple people said that. No one ever said it was good to max your injectors and that everyone SHOULD do it. It's for fuel headroom and I don't see anyone saying it's bad to have that. I was saying your injectors won't die, and now we somehow have agreement on that it seems.


I tune pretty lean anyways with my 2G cause it hates being in the 11's; where my 1G is about the opposite and hates to be in the 12's. Cars with similar setups are sometimes quite different in tuning requirements. IMO timing is a lot more important than fuel when running E85; a bit too much timing and your headgasket is gone (I'll admit to doing that a few times) or something more serious.

Just read the thread again and no one said anything to that effect at all actually.

It was a strawman you constructed to knock down

Glad we have landed on the same page now though, so cheers to that.

Wow. I go away for a few hours to play some pool and drink a few cold ones, and this thread goes viral.

It sounds like everyone is just about on the same page now, but I wanted to make a couple of comments, in the interest of clarification for anyone new to this story. (Actually, I'm just bored and feel like killing a couple of hours rambling in a DSMtuners thread)

jrohner said:

I disagree that in theory my 16 gallon gas tank can hold over 19 gallons. If you get over 100%, then the math is wrong, not theory.

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Ok... maybe my bucket analogy wasn't the best.

jrohner said:

IDC is a function of pulse width and RPM (or time actually), not injector size. Bigger injectors don't change time

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The first half of that statement is true, the second half not so much. (I'll explain why in a minute).

Let's use the first half of your statement to answer an earlier question and show how you can have a theoretical IDC above 100%, even though the injectors obviously can't be open more than 100% of the time available.

The Basics

A mechanical coil-driven device is energized by applying positive voltage to one side of it, and applying ground to the other side. This creates a magnetic field that can be used to do mechanical work, such as pulling on a plunger to open a disk or pintle on an injector. The activating signal (in our case, ground) can either be applied continuously, or it can be pulsed on and off. When the coil is pulsed, the length of each pulse is called the pulse width (or PW). For injectors in particular, the PW is measured in milliseconds (thousandths of a second).

Taken by itself, a pulse width value doesn't mean a whole lot because there is also the interval of time between pulses that has to be accounted for. In a cyclic, repeating system, this combination of on-time and off-time is called the period, and represents how much time there is available between the point when the coil is first energized, and when it needs to be energized again in the cycle. So if I needed to energize a coil every 100 milliseconds, and I keep it energized for 25 milliseconds each time... the period would be 100ms, the PW would be 25ms, and there would be 75ms of time between pulses when the coil is closed and waiting for the next 25ms pulse.

Pretty simple stuff right? Just covering all the bases here.

Duty Cycle

The term "duty cycle" is used in many applications, but for most all mechanical coil-driven devices, it is simply a calculated value that provides a way for us to get an idea of how hard a coil is working, without having to deal with pulse widths and periods. As far as the device is concerned, duty cycle doesn't exist; you can't energize a coil by directly applying a duty cycle to it.

The calculation for duty cycle is very simple; it's just the pulse width divided by the period, which gives the percentage of time that the coil is being energized, compared to the total time available before it has to be energized again. So for our above example, the duty cycle would be 25%: 25ms PW / 100ms period = .25, or 25%

In a fixed repeating system, like a flashing road construction light for example, the PW (on-time of the light) and the period (time between flashes) is always constant; so the duty cycle is always constant as well. In an engine however, the period is always changing...and that is where things get a little more complicated.

Injector Duty Cycle

The amount of time available between injector pulses is based on engine RPM, or more specifically, on engine cycles. Considering that the injectors fire once per complete engine cycle (which takes two revolutions of the crank), we can use the following equations to calculate some useful information:

Revolutions per second = RPM/60
Cycles per second = (RPM/60)/2 or RPM/120
Time available between injector pulses (period) = 120/RPM

Given this information, it's easy to calculate IDC:

IDC = PW/Period, or PW/(120/RPM)

Now that we know how IDC is calculated, lets plug some numbers in.

At any point in time, the ECU is determining the required injector PW based on reported airflow, assumed injector size and base fuel pressure, battery voltage, temperature compensation, desired AFR, engine load, etc. As an example, let's assume that under a given set of test conditions at a steady 7000 rpm, a required PW of 13ms is calculated. Plugging those numbers into our IDC formula, we get the following:

IDC = PW/(120/RPM) = .013/.017 = .765, or 76.5%

So at 7000 rpm and with our set of test conditions, the ECU has 17ms of time available to open an injector, close it, and then open it again at the start of the next cycle. If the injector stays open for 13ms during this 17ms "window", you get an IDC of 76.5%.

But what if under these same conditions, the ECU has smaller injectors to work with? Lets assume that with these smaller injectors, the ECU calculates that it needs a longer PW of 18ms to hit the same AFR under the same conditions. Plugging that into our formula, we get the following:

IDC = PW/(120/RPM) = .018/.017 = 1.059, or 105.9%

What we end up with is a calculated pulse width that is longer than the time available between injector firing events. The ECU is going to attempt to hold the injector open for 18ms, but there is only 17ms available before it has to send the next 18ms pulse. The net result is that the injector never has time to close before receiving another pulse, so it's running wide open. So, we have a calculated IDC of 105.9%, but a true IDC of 100%... since an injector obviously can't be open longer than 100% of the time.

To summarize, an IDC below 100% is an accurate representation of how hard the injector is working. Anything above 100% is irrelevant since the injector is open continuously at that point.

So as you can see, injector size can change time; it can affect the calculated PW, which by definition is the injector's on-time.

*****

As you've probably guessed, that ^ is a greatly over-simplified description of injector behavior. For one thing, the injectors don't just instantly open and close; it takes a small amount of time for the coil to fully energize and open the pintle or disk depending on the voltage, fuel viscosity, fuel pressure, etc. It also takes a small amount of time for the injector to close once current stops flowing through the coil. This additional time has to be considered by the ECU when calculating pulse width, and can therefore affect IDC to some extent. On top of that, fuel flow through the injector isn't always linear with changes in pulse width, which also has to be considered.

Fortunately for us, we have the ECU to handle all of this craziness and to provide us with a simple IDC parameter to quickly evaluate how hard our injectors are working.

Damn, nice Calan. Most of that was explained in my links but you went alil more in depth with it. Lol guess i should have just posted the info. Most ppl are too lazy to follow a link.