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Thread: Bringing it back...LNF Injector Timing

  1. #1
    Senior Tuner cobaltssoverbooster's Avatar
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    Post Bringing it back...LNF Injector Timing

    A long time ago the community was blessed with a lot of tuner interest and activity. Now as GM stopped with the 4 cyl SS additions the interest has died and people slowly started fading away and taking their knowledge and information with them. Credit is given where it belongs here and most of this information was put out by GMTech and the select few people who were around here when he was doing the most of his table testing. It took a while for people to get interested in the topic again, so digging up the information and doing a little testing to verify the thoughts took some time to get it all put back together. So the rambling ends and the info begins!

    LNF Direct Injection Window Base Operation

    The crankshaft for most people is viewed as a 360* object. TDC is at 0*, BDC is at 180* and again TDC is at 360*/0* again.
    This is a misconception that has arisen from what i believe is the camshaft degree wheels doing. The Normal Camshaft Degree wheel is numbered in two ways.
    First Design: TDC is labeled as 0*, and BDC is labeled as 0*. the midpoints between the two (after TDC to BDC midpoint and After BDC to TDC midpoint) are labeled both as 90*. This edition camshaft wheel takes a little bit of math as the user usually has to do a slightly longer conversion formula when trying to find the cylinders true TDC.
    Second Design: This is the design that i blame for the 360* train of thought. TDC starts at 0*/360* and as you rotate clockwise it counts down from 360*, passing BDC at 180* and reaching TDC back at 0*/360*.

    Now, the way it really works and everyone should be viewing it as:

    Since the crankshaft is twice the speed of the camshaft (2:1 ratio), it is officially proven and known the the crankshaft does 360* twice when the camshaft does 360* once. The fuel injector is opened and closed on a degree based event just like the camshaft so thus we can plot its operation out just like a camshaft. So now the crank is a 720* rotation when the cam is only 360*
    I'm going to plot a camshaft from a standard comp cams degree card which is used on a GM Ecotec LSJ Turbo application to help with the visualization process. This camshaft is XE246THR-13 and is an Xtreme Energy Camshaft for 2.0 Turbo applications. The .050" Values will be used for the example.

    The Cam Plot on a 720* Base:
    First the Overlap event on the camshaft takes place at the 360* mark. Compression sweeps through into 0*/720* where you get a spark event and start the power stroke which leads back into the overlap event at 360*.
    So with the information the card gives us the intake cam center line is 112*. the 720* plot for center line puts this value at 248* IVCL . Divide 204* duration by two and you get 102* each direction for opening and closing * values which would be IVO at 350* and IVC at 146*. The exhaust is 113* separated so the center line is 361*. Halve the duration of 200* is 100* from the exhaust center line. This plots out as EVO is 461* and EVC is 261*.

    when plotted on paper it looks something like this:


    Now if you plot the opening values for the direct injection on the same chart you can see where the injector is starting to fire off during the cam event.
    The minimum opening angle allowed is 240* and the maximum angle allowed is 431*. The DI Opening Angles got added to my previous plot and it looks like this:



    Note this particular cam has 89* of overlap and is not a suitable choice for the Direct injection operation as the injector spends a lot of time spraying while the exhaust valve is open. Due to less overlap in the park position of the factory cams we can automatically see in our heads that the factory cams are better suited as the exhaust is more advanced thus letting the Injector spray more during the intake cycle than the overlap cycle where some energy is wasted. The camshaft events for direct injection face more deciding factors than that of a runner injection system like the lsj has. the lsj can have the exhaust retarded more as the fuel is sitting behind the intake valve where it waits for the valve to open before it enters the cylinder. this older setup can have more overlap to help flow out turbochargers as it helps draw that sitting fuel in where in the direct injection system its already in the cylinder so if overlap is occurring the fuel has a more direct exit. the piston shape helps divert the fuel upward into the cylinder head which should help keep it from flowing straight out the exhaust valve but there is a bigger loss in this system. cylinder temps also have a bigger play as after compression and ignition the piston dome is hot and fuel coming into contact with a hot piston can cause pre detonation. the oil passage in the piston head helps with that as well. overall the direct injection system has way more variables to think of when modifying both physical parts and calibration data.


    With all this data presented in a form that is easy to understand by visual form you should now understand exactly what the Injection Angle Table Values mean and you can adjust them accordingly. The adjustment of these values drastically helps Knock Retard situations. If you increase the window angle by raising the value you will spray the injector before the cylinder gets really hot from dynamic compression and thus prevent the event of detonating bad fuel put out by today's gas stations.

    I will be posting another Direct Injection post shortly to help everyone choose a side on the Direct Injection Event most commonly referred to as Injection/Spark Over-spray. My post requesting log information from turbo swap vehicles is to help plot data for this post. The more Turbo Swap logs i get with basic information will help me get the post up faster so if you know someone with some good logs that meet the qualifications please pass me some info so i can finish the information.
    The Qualifications are listed in this thread: http://www.hptuners.com/forum/showth...-Data-LNF-Only

    Alex Johnson
    CobaltSSOverbooster
    Photos Attached to Post so they can be viewed larger ad/or rotated for ease of viewing.
    Enjoy!
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    Last edited by cobaltssoverbooster; 10-24-2013 at 07:14 PM.
    2000 Ford Mustang - Top Sportsman

  2. #2
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    You plotted your diagram backwards. The exhaust valve should be closing as the intake valve is opening, and a higher number injection angle is more advanced.

  3. #3
    Senior Tuner cobaltssoverbooster's Avatar
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    second paragraph from the bottom:

    With all this data presented in a form that is easy to understand by visual form you should now understand exactly what the Injection Angle Table Values mean and you can adjust them accordingly. The adjustment of these values drastically helps Knock Retard situations. If you increase the window angle by raising the value you will spray the injector before the cylinder gets really hot from dynamic compression and thus prevent the event of detonating bad fuel put out by today's gas stations.

    basically says the same thing you said just not as clearly so thanks for clearing that up. Raising the Injection Window Value will start the Injector opening sooner(advancing the window).

    as for the graph it is plotted correctly. It counts down from 720 - 0 where it starts at 720 again. I drew it as if it were being scrolled to the right (like the crank rotates clockwise) so you read it from right to left. At the right the exhaust opens first and as its closing in the middle the intake is opening for overlap event then the intake closes on the left. The value marked IMO 240* is the smallest window allowed by HPTuners for retarding the injector start. the IMAXO 431* on the right is the max opening angle allowed or fully advanced Injector start.
    2000 Ford Mustang - Top Sportsman

  4. #4
    Senior Tuner cobaltssoverbooster's Avatar
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    Here is another file that is quite interesting. For the mass majority of the crowd stock turbo or aftermarket turbo i see a maximum of 7.8ms on the injector duration.
    Here are a few logs plotting the max Injector ms duration vs rpm. The first one is Stock Turbo running Methanol Blend and the second one is AM Turbo running a TTR Intake manifold. Not sure the fuel on the second graph but the info shown will help prove a point coming up.

    E47 Stock Turbo.pngTTRMan Full BoltOns.png

    so as everyone can see the max values between both are:
    2520=5.4/3000=4.4/3520=5.9/4000=6.0/4530=7.3/5000=7.2/5520=6.8/6000=6.3/6520=6.3

    now i have converted rpm into a time factor and used the max ms per rpm to determine how many degrees the crank rotates in correlation to the duration of the fuel injector in ms. File is the excel sheet attached.
    if you go to sheet 2 and look at the plotted data you can see i have highlighted the values above. Remember from the first post i said the minimum or fully retarded injector window period was 240*. 0* would be top dead center and in most exotic fuel cases i will call 26* the maximum allowed wot timing. I use the 26* as a worst case highest timing scenario. Therefore if the window is fully retarded at 240* you have 214* of spray time before the fuel injector sprays during the spark ignition event. If the minimum window value is used you would run into this event at around 4500-4800 rpm. The truth is that under wot conditions the factory degree window is in the 340-360* range. That means you have 314-334* of spray time before you run into blowing the spark out. the first 334* value in the chart doesn't show up until about 6200 rpm and 9 ms of injector on time. That is a ton of time! Therefore with logs from people running tunes at a DD level this event will never happen. Now that isnt saying people making full out race application pushing boost way over 30 PSI are going to never see this event. It is a Possibility to run into the event everyone is claiming but its going to take a heck of a lot of fuel injector on time and most likely a lot of boost. Boost levels Matt is probably more familiar with than anyone.(~40 psi +)

    Id still want to see some more logs from High Boost Turbo Kits running Ethanol Blends to help by having more data plots. The logs shown went to a max of 27.5 psi and highest rpm of around 6500. If anyone goes higher in either i would love to see just the log so i can plot the new data. I will be changing the scanner histogram to add the same rpm values plotted in the chart i made in the excel file so data can be plotted in a colored line through the entire chart.

    So far the injector spray through everyone seems to be experiencing is not the cause of injector misfires. Before this data i thought that was happening. Information changes everything.

    Alex Johnson
    CobaltSSOverbooster
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    2000 Ford Mustang - Top Sportsman

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    You also need to consider the amount of time it takes for fuel to travel from the injector to where it needs to be for efficient combustion to take place. I do not know the velocity of fuel traveling away from the injector, but I do know that the time it takes is significant in this situation. Even at 100mph, it would only move 1.76" per ms. I imagine that coming out as a mist that the fuel also slows down fairly quick as well.

  6. #6
    Senior Tuner cobaltssoverbooster's Avatar
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    I didn't calculate speed of atomized fuel travel at rail pressure. Contact with the piston also would need calculation for natural drag coefficient but I don't know that value but sure it will change with fuel base quality and type.

    Good information to keep in mind thanks Matt.
    2000 Ford Mustang - Top Sportsman

  7. #7
    Tuner noorjSS's Avatar
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    Good read, thanks man
    2006 Chevy Cobalt SS 2.4 Turbo
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    damn nice work man

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    Advanced Tuner projectlnf's Avatar
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    now if we could just figure out how to make a PID in the scanner to calculate when our injectors turn on.. that way we can go back check the log figure out when they turn on and how long they are on and what our timing is at that point.. and bam.. we can tune the angles more efficiently .
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  10. #10
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    Fixed my knock issues using the injection angles. I do get some fake knoc from the balance shaft delete, although. I wish i didnt delete those damn things.
    Last edited by PyroMechanic; 11-28-2016 at 07:06 AM.
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    Advanced Tuner lt1z350's Avatar
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    I have been trying to read up on this for my ltg and was told by guys doing more c7 stuff that it is a very important adjustment on bigger turbo cars even anything fi stock or not can stand to have some worth to the soi table. My car having a larger turbo I still am no where near optimal on it and still lacking a lot due to not setting up things like vvt and injection timing for the larger turbo. So much to read and hard to figure out what to log and then turn into data for changing it properly. One did say logging ms and where u see a drop off advance timing. But that is just part of it I assume. No one just gives a direct answer. Also vvt tuning my ltg is different then the typical ltg so reading up there only goes so far for my setup. But glad this is being talked about more for sure.
    First 9 second 6th gen lt4 zl1 stock blower SHC SBE boost only.

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    2017 zl1 a10 big gulp/2 inch headers/ 9.55 lower/ e85/bigger hx /103mm tb / Synergy trunk tank and underhood kit/methanol injection with torqbyte controller and prometh pump / Jokerz performance R&D ported stock blower/ lme cnc heads /GP tuning custom cam. So far 9.30@150