Ok guys i have been doing some loggin and some checking and came up with this conclusion.

1.) if you adjust your IFR table to get your ltrims in line (0 or slightly neg) the you directly effect the ratio at which the PCM injects fuel and the size injectors the PCM thinks it has.
2.) therefore your injectos max out.

e.g., I scaled my IFR table to make my computer think my injectors were smaller to give me more fuel to get my ltrims in line. Now that my PCM is saying "ok ive got x injectors i need to pulse them x.xx MS to get the right flow" Problem is now that i have made the computer think they are smaller its also saying "pulse higher ..PULSE HIGHER" when in reality it doesnt need to pulse that high a MS. SOO.... my ABPW is reading 18ms at 6krpm and by any chart thats maxed..but in reality they arent because they can still handle more physically the PCM just doesnt know that because of the new coeffiecient plugged in it.

My secenario: My injectors are showing 100% duty cycle with my HC setup (430+rwhp) ive got a 98 so i "should" be able to hold 460rwhp. Can someone answer this??

 

IMO, people need to pay alot more attention to fuel/air ratio and fuel pressure at the rail (keep it above 55 PSI at all times!) and forget trying to calculate duty cycles. How often have I preached that you're NOT maxed out just because you have a heads/cam car making 420 RWHP+ and a calculation or Autotap gives you the idea that your injectors are maxed even though you still have enough injector capacity to wash the damn cylinder walls down if you want to? Man, I'm getting blue in the face about this one.

Now don't get me wrong, I understand you people that are scared to run these injectors above 80% max for fear of locking them up (which, btw, I've NEVER heard of happening with an LS1 running 60 psi or less) but still, you can't say an injector is "maxed out" when it still has enough capacity left to spray a 50-100 HP dry shot on top of what it's doing without running lean.

Ok, off my soapbox. There's nothing wrong with running 42 lb injectors with 420 RWHP so go ahead if it makes you feel warm and fuzzy. Just don't tell my I'm nuts if I break 500 RWHP with the stock injectors (that's been done many times, BTW)!

 

Colonel:
I have to disagree with that to a point - injector duty cycle is a very important thing to monitor when sizing injector. For what 99% of people here are doing, I agree - you don't need to set a top limit of 80%. That's more of a guideline to use when actually sizing injectors - though normally it comes down to what sizes are available at what price. I would put the cap somewhere higher - 90-93% or so for a drag application. Can you see higher values without things blowing up? sure, but your injectors probably aren't flowing anymore - and they are likely going static. Will they still work? More than likely, but again, it's a good indication you are in the danger zone. Injectors are cheap compared to the price of a motor, so why push it?

Rail pressure is also important to monitor, but that won't really tell you anything about the injectors, rather, it will tell you if your fuel pump can supply adequate volume.

Also, as a point, just because somehtign will work once or a few times, or even for a few instances doesn't mean it is the best way to go - if you looked at it on average you would have a higher amount of injector related failures running at 90+% duty cycle than if you were at 80 or less. It wouldn't be any fun to be that 1 out of 10 or whomever who has the problem and pops a piston! In a NA setup it's not as big of a deal, but in a power adder setup that's a very real consideration.

Your points on a/f ratio are dead on though - and that needs to be set before you worry about pulsewidht too much (as long as pw is reasonable). I just don't think one should disregard injector DC, or try and squeek by on the absolute smallest injectors.

stangkillin99ss
As colonel mentions you need to get your setup tuned via a/f ratio. Sure it may command an initially higher pulsewidth than needed, but then your PE vs RPM table would be lower than it would otherwise - thus reducing the commanded pulsewidth. If your a/f ratio is accurate than your injector DC is a good indication of safe HP capacity. As was mentioned you *may* succesfully be able to push them higher, but why, when svo 30's, etc. are so cheap?

 

colonel:

I understand what you are saying and i dont disagree. I too believe these injectors can handle alot of HP. However i think you took my question the wrong way or i phrased it wrong.

My assumption was that my injectors arent really maxed out despite the fact that everyone says "18ms and 6k they are maxed". All the charts out there say this, but i dont agree. The charts that everyone goes by says this is true but the computer knows what injectors it thinks it has and the ms is for that specific ratio (in the IFR table) so what im saying is how can people say "at 18ms @6k rpm they are maxed" if everyones coeficient is different? (from the IFR table) Maybe the charts are true for stock table settings but what about if they are adjusted?

 

Chris, I agree with everything you said there. Don't misunderstand me, I'm NOT advocating running things on the ragged edge of safety. I just want people to have an accurate and realistic understanding of what these fuel systems can do and the danger (or relative lack of danger) involved in running the injectors beyond what some people think they are capable of. In a nutshell, it bothers me that there is a somewhat common belief that stock injectors, even the 28.8 lbers, will safely support operation in the 420-430 range and no more. That is just false and that's my point. I've become a bit frustrated that oftentimes people think their injectors are totally maxed out due to some calculation or PW monitoring when in fact, their injectors will support more.

Now running a power adder, sure, overkill on the fuel system is JUST RIGHT! I've always been an advocate of that. But running NA, you're not going to be running a nice 13:1 fuel/air at 450 RWHP and then all of a sudden an injector stops flowing and you melt a piston. It just doesn't happen...well, anything is possible, but you get my point.

Regarding fuel pressure. Sometimes people *think* their injectors are maxed out because their duty cycle is maxed. Well, if the fuel pressure is 45 psi, you have to increase the duty cycle to maintain the fuel/air ratio. If you bring the psi back to 55+, where it should be, you can bring the duty cycle back down. Were the injectors maxed? Maybe so. Was it the fault of the injectors? No, the fuel pressure was low. How many people running serious power have a pillar mounted FP gage? Not many...but everyone running a PA should have one and it's a really good idea for anyone.

Since we're on the subject, who has had an NA LS1 engine failure due to an injector failing due to being run at a high duty cycle (injectors can fail for other reasons)? I'm sure it's happened before but in my years, I've NEVER heard of it. Not even with all of the 470-520 RWHP large CI engines running around with stock injectors. Why? Because when people notice their O2 readings are lean, they upgrade their injectors and pump. The ones who've not reached the point of leaning the mixture back excessively (even if their injectors are doing all they can) seem to run like this indefinitely and without problem.

 

...But am I telling you that you absolutely will not have a problem with running an injector at 95-100% of what it can actually do (I'm not talking about calculated DCs here)? No, I absolutely am NOT saying that...but I'm not at all scared to run it like that based on years of observing what myself and others have gotten away with. To each his own level of risk.

 

Colonel - definitley - and on a NA setup I would be way more inclined to push the limit - it's just that 30lb svo's are so cheap that it's almost a gimme. But yep, otherwise agree with everything

stangkillin99ss - the pulsewidth is how long the injector is open - depending on how fast the motor is turning there is only a fixed amount to get the fuel in - doesn't matter the injector size. Now a bigger injector should open for a smaller amount of time, yes. If you lie about the injector size the computer will open it for longer than it should - then you will be rich. If you then tune the pe vs rpm to get the a/f ratio correct then that table will lower the pulsewidth - so regardless of what you tell the computer the ifr is if your a/f ratio is correct then your pulsewidth is an accurate representation of injector usage. Just think of it as a percentage - e.g. "I am using xxx percent of the injectors available flow rate".

Also, fwiw, 18msec at 6000rpm is 90% duty cycle - 20msec would be 100%.

 

20ms at 6000rpm is MAXED. If your pcm shows 20ms or more at that rpm they can't be held open any longer. Think of it as just applying 12 volts directly to the injectors. They are open, plain and simple. But you can't do that for road racing or for very long or they heat up. Well from what I always read anyhow. I used to supply 12 volts directly to injectors for auxiliary setups and never had any trouble.
When I say mine are maxed I mean the injectors are static. I personally have not had a problem running injectors at 100% for drag racing and I have done this for a long time. You would actually want them static vs high 90% duty cycles. Once their held open 100%, fuel flow is fine but no longer adjustable. It's when they are just before static that they might flow poorly and erratic.
If your injectors are at 100% duty cycle then "injectors" are maxed, meaning they can't deliver more fuel if needed. But this doesn't mean your power from the injectors is maxed.
If they continue to support more HP at this point it's simply because the motor is capable of running at a leaner BSFC.
When most people calculate BSFC they use about .5lbs per hp N.A. which is actually sort of rich for a modern engine like the ls1 IMO.
If you run the motor to a .44 BSFC then you could squeak out 523 FLWHP from 28.8LB injectors.
.44 BSCF is about a ~13.5 a-f. It's also possible the stock injectors might flow a tad more than advertised. Don't know as I never flowed them.
But make it very clear, fuel makes the HP. Cams,heads,cubes,blowers and nitrous, just allow more fuel to be burned to make more HP.
Steve

 

Actually, 20ms @ 6000 RPM isn't physically maxed out for the injector, it's 50% ... think about it -- it's the max open time for that HALF of the engine revolution. The PCM obviously knows it can hang the injector open longer, because it DOES -- and the motor doesn't starve for fuel where it otherwise "theoretically" should. In order for the injector to go mechanically static (ie. open 100% of the time) your duty cycle would need to be 200%, or have a 40ms pulse width at 6000 RPM. As duty cycle increases, you spray more and more fuel on the back of a closed intake valve. Is it optimal? Heck no, but it works.

 

THANK YOU BRIAN!!!

Finally, a logical reason why I can make an engine run RICH beyond 100% DC if I want to (which goes against the "you can't open an injector longer than 100% DC theory that is SOOOOO obviously false to anyone who's tested it.) Think about it folks....take an engine to 100% DC at a 13:1 fuel/air ratio. Now, increase the PW even more. What happens? The thing gets RICHER. Yes, it does. Try it, you'll see. That wouldn't be possible if the injector were truly spraying 100% of the time as has been commonly believed to be the case when it is at 100% DC now would it?

Once again, thanks Brian. I now know WHY what I've been saying to be the truth for years IS the truth.

 

not trying to argue or anything but i have some info to share. at this link http://www.supras.com/~riemer/sonict...rs/RCtech.html is some great injector reading. one paragraph i really liked is right here.

"NOTE: Most pintle injectors will increase flow rates up to 88%, 92% with Disc injectors, and then go "semi-static", half open-half closed, just before going full static. This time-out event occurs at different time/pulse width durations, in different injectors, but always produces a 50% or so Duty Cycle flow rate. This extremely dangerous situation will usually occur at the worst of times, full throttle-max boost-high RPM- just when you need 100% fuel delivery you get 50% and go dead lean. BANG!!! This problem seems to amplify a bit at higher pressures. "

also, there is only .02 sec of time between 2 full revolutions at 6000rpm so 20ms is all the time there really is for the injector to fire.

6000rev/1min = 2rev/x x=.0003333min(time or 2 rpm)

.0003333min x 60 = .01999sec

 

would it be posiable that the reported pulse width on atap isn't correct, i know there is a certain amount of time it takes to get the injector open(injector offset), what if that time is added to what we see on atap so it is reporting that it is open longer than it really is.

i see numbers like .25 in edit for injector offset at 14.5volts. what time interval is that number? if that is ms then the actual 100%duty cycle would be 20.25ms at 6000rpm and that doesn't really expalain what you said above. hmmmm, something definately doesn't calculate out here. anyone have a scope so you can just back probe one of those injectors and see how long it is really open compared to what is being reported.

 

Whoa, settle down there Colonel , Brian you have the wrong logic.
It takes 2 complete crankshaft revolutions to complete the entire 4 cycles.
This means at 6000 engine rpm there are 3000 COMPLETE intake,compression, power, exhaust cycles taking place in each cylinder.
That's 50 cycles per second or 20ms per complete cycle.
So an injector open at 20ms at 6000rpm is open the entire time of the 4 cycle event spraying the back of the intake valve( intake,compression,power and exhaust) and then the next cycle begins.
Here is the simple math for time available to complete all 4 cycles per a given rpm-
120,000/rpm

And if you can't get this straight, then simply go and get any DMM that reads duty cycle and hook it up to an injector.
It will read 100% open at 6000rpm if you see 20ms! Before I had my ls1 I used duty cycle meters on my Ford.
To bad the pcm does not output duty cycle instead of P.W.
It would be a whole lot less confusing.
The opening offset is a separate table and used to define the commanded PW.

The pcm will "command" PW higher than 20ms at 6000rpm. However it is doing nothing because 20ms is all the time availble to injector before the next cycle begins at 6000rpm.
Steve

 

Yep, calm down Steve has it correct above - 100% DC is just that - 100% DC. You also have to remember that the injector is an electromechanical device so you need some time for the coil to move, reset, etc. You can hang it open all the time, but that isn't the best for coil life, etc.

20msec @ 6000rpm is all you get!

Chris

 

FWIW

1 second = 1000 milliseconds
.02 seconds = 20 milliseconds

I wonder about the following...

If an injector is rated at 28.8 pounds and all injectors are rated at 43.5 psi, would this imply that the same 28.8 injector at 58 psi would actually be a 38.4 pound injector?

Seems like the LS1's higher fuel pressure and what injectors are rated at might be the key to how these "little 26's & 28's" can actually make 500rwhp when tuned exactly right.

 

most of the flow numbers you see are at the higher ls1 fuel presure. and even if they wern't if the thing is properly tuned with a wide band at WOT and it is showing 20ms pulse width then it should be out of injector.

 

Well damn, got myself all worked up over nothing I guess.

Yes, the higher the pressure, the higher the volume for a given injector...but, I've always thought that GM rated these injectors at 58 psi unlike Ford who rates theirs at like 44 psi...but maybe not?

Anyway, all this doesn't explain why you can record a supposedly maxed out injector and then continue to add a fair amount of power without leaning the mixture...even richening the mixture if you please. I'm now back to, "I don't know the WHY...I just know that it IS."

 

Anyone actually tested a 28 pound injector at 56 psi and measured how much fuel it delivered?

If the 28 rating is based on a fuel pressure of say 43.5 psi then the same injector with 56 psi would be ~ rated at 36. I get this by cross multiplying and dividing...ie 28*56 divide by 43.5 gives us the injector rating of 36 pounds at 56 psi

At ~17 hp per pound of rating...our 28 pound injector should be able to support 612 flywheel horsepower maxed at 100 percent under ideal conditions because it's really a 36 pound injector with our fuel system. ie 36 * 17 = 612 flywheel hp

612 flywheel is about 520rwhp with an M6 at 15 percent drive train loss ie 10-bolt rear

612 flywheel is about 501 with an M6 and 18 percent loss ie 12 bolt rear

I think someone made ~500rwhp with a stock injector at some point.

I have no idea if my guess are right about the injector ratings being at 43.5 psi but the math works and matchs what has been observed real world.

Do we basically have 36 pound injectors with our fuel systems due to the high pressure?

Other thoughts?

 

This is a good thread (OLD). I though the injectors only opened for 1 cycle but 100% duty means they are open for 2, hence the injector is always open!

Joe

 

what I saw on the flow bench, when I did the ASA/LS1 spec engine injectors. I flowed them at 60psi, and got the above PPH values.
The dyno tests showed the engines in the 460FWHP range...

Just my $.02....