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Thread: End of Injection Timing Open Discussion

  1. #76
    Fuel Injected! Stroked 388's Avatar
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    Quote Originally Posted by WASyL View Post
    also found this on HPTuners board for LS1 PCM but actually it apply to any fuel injected engine:

    - By adjusting (increasing) EOIT "Normal" , you can reduce or eliminate most exhaust smell at idle when not running cats on a cammed LS1
    - LS1 PCMs are limited on what you can control, not 1 value solves all
    - .11 = 10 degrees of crank rotation
    - Leave the "Injection Timing Boundary" at 6.50 (stock value)
    - Leave the "Makeup Injection vs ECT" at (stock values)
    - Don't oversize your injectors for your application
    - The bigger the cam and more overlap the higher the "Normal Injecting Timing vs ECT" values
    - EOIT normal values can range from 6.0 all the way up to 6.5, depending on valve events

    best regards
    Now I'm confused your saying we need to add to the eiot ? Not re move. I don't have hp tuners I'm using eehack so I'm guessing the eiot definitions are different on how they are displayed I don't see a normal or injection timeing boundary in eehack only the eiot vs temp

  2. #77
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by Stroked 388 View Post
    The reason to spray on a closed exhaust valve is so the gas can vaporize from the heat of the motor witch will give more compleat fuel burn.
    I think you're confusing some concepts here.

    Spraying on the closed intake valve gives better evaporation of the fuel charge. It seems with aluminum heads the longer the fuel has to evaporate, the better.

    The idea behind spraying after the exhaust valve closes was to prevent raw fuel from being drawn into the exhaust at low airflows. My hope was someone would find it also helped with surge, but I think everyone that's trying it loses driveability. See my comments below regarding tau and transient fueling for why.

    With a late EOIT setting such as BDC of the intake stroke there will inevitably be injection spray while the exhaust valve is open at higher airflows (and hence higher injector PW). But the same can be said of early EOIT (closed intake valve).

    There are a lot of dynamics involved here. One can't simply change EOIT without remapping the VE table or adjusting the tau model because the fuel that remains in the port when spraying on a closed intake valve works into the ecu's fueling equations. When you spray fuel directly in the open intake valve the amount of fuel remaining in the port decreases significantly. Mitch, this is why you saw pulsewidths decrease when increasing EOIT. EDIT: To state it in a way that makes more sense, you saw pulswidths increase as you decreased EOIT or injected the fuel later. Unfortunately a late EOIT strategy (after exhaust valve closes) will throw the tau modeling way off and transient fueling will suffer, affecting driveability.

    Quote Originally Posted by Stroked 388 View Post
    Now I'm confused your saying we need to add to the eiot ? Not re move.
    I believe that info that WASyL quoted were generalized guidelines. I'm beginning to think there's no magic bullet here as I once thought.

    Quote Originally Posted by Stroked 388 View Post
    I don't have hp tuners I'm using eehack so I'm guessing the eiot definitions are different on how they are displayed I don't see a normal or injection timeing boundary in eehack only the eiot vs temp
    The tables mentioned by WASyL were relevant to LS1 pcms. There may be equivalent tables with the $EE mask but eehack only allows realtime adjustment of EOIT. It's a transient setting that gets reset when you shut off the key - once you settle on a value you should change the table in whatever bin editing tool you use (HPTuners being one such tool) and reflash your tune so your changes are permanent.

  3. #78
    Fuel Injected!
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    found on HPT forum (link: https://forum.hptuners.com/showthrea...l=1#post317191 ) but it is quite good explenation in degrees we use on EE

    Quote Originally Posted by Monty
    Was really wanting to understand what everyone was saying in this LONG thread so i could add things up more correctly with the overlap numbers, rather than just guessing around..
    Quote Originally Posted by pontisteve@HPTuners board
    To put it into context, the whole thing is about vaporization of fuel in a stock setup, and about not throwing out fuel on the cammed up side.

    In a stock rig, the injector sprays onto the back side of an intake valve. Both valves are in contact with the heat from the combustion chamber, but only one valve ever looks like it's been hot, right? That's largely because the intake valve is being cooled off with fuel, and nothing cools the exhaust valve directly.

    In stock form, it's about turning raw gasoline (liquid) into burnable vapors (gas). Raw liquid gas doesn't burn, only the vapors do. So we use an injector at 58 psi to turn big gulps of liquid fuel into small droplets of gas. EFI and it's high pressures do this wonderfully to begin with, compared to the raindrops of fuel coming out the bottom side of a carb, right?

    Then we spray this fine mist in a cone pattern onto the back side of the intake valve, and we shape the cone to hit near the edge of the valve, by the seat. This way it cools off the hot sharp edge of the valve, and as the valve opens, the air flowing in tends to shear the droplets into even smaller droplets.

    Since the cool fuel hits the hot valve, it tends to vaporize and become a gas. So picture it in your head. The intake valve is closed, the motor is idling, the injector PW is maybe 2 - 4 milliseconds at idle, and the injector delay table is programmed to spray onto the valve just before it opens. This way, other cylinders going up and down don't inadvertently steal the air and fuel vapors out of this intake runner.

    The injector will have a start time and an end time. The delay table back-calculates the injection timing. So let's say the intake valve is going to open at X degrees of crank rotation in the engine cycle, and the engine is idling so it only needs 3 ms of pulsewidth. The injector would END its spray pattern just before X degrees rolls around. So it would have to START it's spray pattern at 3 ms before X in order to finish by X. If the pulsewidth jumps up to say 15 ms at WOT, then the injector would finish by X still, but start at 15 ms before X.

    Here's where it gets interesting. You can calculate the engine speed, the 720 degrees of crankshaft rotation (the cam runs at 1/2 the speed of the crank), and you can figure out exactly how many milliseconds (ms) of time becomes how many degrees of crankshaft rotation. That's just math. So if you're only idling, that start and end of injection time (SOIT and EOIT) will be very close to the time when the intake valve is about to open.

    So picture the closed intake valve, the injector opens for a few ms before the intake valve opens, and it closes just before the intake valve opens, making sure that fuel is now vaporized, broke up into little bity pieces, and basically a gas cloud at this point. Then the intake valve opens, that gas cloud immediately gets sucked into the cylinder, and it's ready to be exploded.

    Now picture a cam change. We have a cam with a lot of overlap (because it sounds cool at the local drive-in). The intake valve and exhaust valve are now open at the same time, in a way the factory never intended. The intake manifold has vacuum in it (at this point, that vacuum is coming from the other cylinders!), so the intake runner is in a state of low pressure - vacuum. The exhaust system on the other hand, has high pressure in it, from those other cylinders firing and trying to get out thru a small pipe, causing some backpressure.

    Now both valves are open at the same time, so the high pressure goes towards the low pressure. That means the exhaust goes in the exhaust port backwards, goes thru the combustion chamber, and exits out the intake port. It pushes some of this nice vaporized fuel cloud backwards, up into the intake manifold. (This is called reversion or standoff in carb speak). But that doesn't last long, and then it reverses direction and the intake charge now gets sucked out the exhaust valve instead.

    But our computer calculated just the right amount of fuel, no extra. So we can't afford to lose any fuel out the exhaust valve, or the cylinder runs lean. So we end up richening up idle to compensate for the lost fuel. This is why cammed up cars like to be richened up at idle and low speeds.

    We could move the injection timing back some, so that we don't inject fuel into a valve that has already opened. And that might be good, if we have a longer duration cam than stock, but we don't really have any more overlap. So maybe for a mild cam, that works well.

    But if we move EOIT back like that, we make it more likely that the other cylinders steal fuel from our intake port. We also still have the problem that as soon as the intake valve opens, some of that fuel is going to go right out the exhaust anyway.

    So if the cam is pretty big, we go the opposite way of common sense. We inject the fuel later, onto the back side of an intake valve that's already opened. Why? Well, with longer duration, we can't start the injection any earlier, or we'll end up injecting on the previous engine cycle, where the valve is still open from the last time. So we're going to lose some of that fuel vaporization by doing this, but we are going to be able to time the injection more properly to the longer duration cam.

    We're also not building up that cloud of fuel, just so it can easily get pushed back up the intake, or straight out the exhaust, as soon as the valve opens. Better that we spray it in as we go, instead of 'building it up just to get stolen' all at once.

    On here, guys are trying to time the injection so that the exhaust valve has already closed. So that means a few degrees after TDC, instead of a few degrees before TDC for EOIT to happen. But what I think is being overlooked is the fact that at WOT, the injector duty cycle is supposed to be roughly 80%, right? So the injector is open 80% of the entire 720 degrees of crankshaft rotation. Which means it must START long before the intake valve opens, and end long after the exhaust valve closes.

    Because of this, I theorize that it's not really about the exhaust valve open/close points, as much as it is about starting the injection at the right time (to match the new cam opening/closing points), and about not having the cloud of fuel stolen or completely evacuated out the exhaust valve.

    More common thinking is that it's only about the overlap period, and losing so much fuel out the exhaust, and not so much about having fuel stolen from the intake runner by other cylinders (or pushed back up the intake by exhaust pulses during overlap).

    At higher speeds, all this stuff sort of works itself out. But at lower engine speeds, the overlap may be the exact same amount of crankshaft degrees, BUT the amount of actual time it takes to pass thru those degrees (a product of RPM) is much longer. So it's sort of like trying to play ping pong in slow motion. It just don't work.

    My best guess about what to do here is to experiment with EOIT by slowly adding to it, making the injector start and end it's on-time later in the engine cycle. (Unless you have a mild cam, then maybe go the other direction). I would start by adding 10 degrees of delay at a time, and monitor the results. If you are improving the situation, you'll notice that the engine is getting richer on the wideband.

    This is because the correct cylinder is actually GETTING the fuel you injected for it. So an increase in a/f ratio is an indicator that you're improving your situation. Obviously, you'll end up going back to your airflow model and leaning the car out to compensate eventually.

    If it liked 10, add another 10 and see what happens. It's tough to say exactly how much a motor would like, since all cam overlap periods are going to be different. But somewhere between 20 and 40 extra degrees sounds about right.

    ...

  4. #79
    Fuel Injected! Terminal_Crazy's Avatar
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    Hmm. I relooked at this recently as it was discussed on a FB forum. The following may make some sense:-)

    I stuggled to work out which way round to look at the timing calculation, You can calculate the values from either end of the 720 degree cycle... especially if you think or expect it to finish on the closed intake valve.

    Scott's (spfautsch) comment made the most sense that the LT1 sprays into the open cylinder. The PCM XDF has this set at 180 (#63) WHEN at temp 68C + Up THIS IS THE END OF INJECTION at BDC on the intake stroke.

    Now when the motor is colder it brings the EOIT earlier in the cycle SO IT CAN SPEND TIME spraying onto the valve. At this early stage we are warming up so have shitloads of extra fuel not to care about losing it out the exhaust & the extra fuel helps heat the cat and O2's and exhaust etc.

    Now my calcs gave a better mixture at idle but i think at wot i was still spraying as the piston is coming back up. I've put it back to 180 BDC value for now, so all the fuel is drawn into the cylinder with the intake inertia.
    The LT1 has a fixed position for EOIT only varied by temp.

    Also as I have bigger than needed 42lb injectors I'm no where near 80% at WOT & my injection time is a lot shorter as a result.
    Idle is around 1.7-1.9ms.

    HTH.
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

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