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Thread: Start of Injection calculator

  1. #1
    Senior Tuner DSteck's Avatar
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    Start of Injection calculator

    I'm throwing this out there to get some people to give this a shot and see what it does for you. All this does is allow you to enter operating conditions (shown in blue) and have it spit out some values. Basically, the calculated Start of Injection value is based on starting at a point when there will actually be sufficient time to inject the charge before the cut off (which is 5° before the spark fires).

    Being that a lot of the tuning for this is strictly "try and see", this is intended as more of a visual to make sure that you aren't starting the injection too late for the given conditions. Nothing will fix low fuel pressure, and you may run into issues by moving the injection window in a certain direction.

    This one is set up for factory LT1 injectors in a C7 (just added one for LT4 as well). Short Pulse Adder is not taken into account because ultimately, it only amounts to a fraction of a degree of crank rotation, so I consider it inconsequential for the purpose of this spread sheet.
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    Last edited by DSteck; 02-24-2015 at 12:40 PM.

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  2. #2
    Senior Tuner Ben Charles's Avatar
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    Dave I played with some values, but nothing is populating??

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  3. #3
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by Ben Charles View Post
    Dave I played with some values, but nothing is populating??
    Only the fields in green on the left are calculated. The two tables shown are copied straight out of a tune file, and are only present to develop some equations for use with calculating the modifiers for fuel flow and pulse width (it's easier to use an equation than it is to look up and interpolate from a table).

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    Quote Originally Posted by Ben Charles View Post
    Dave I played with some values, but nothing is populating??
    I'm having the same issue. All the green cells are showing either #VALUE! or Err:502. All the blue cells are filled, and I tried changing some of the values.

    Regardless, thanks for all your efforts to help this community Dave. It's always appreciated on my end.

  5. #5
    I think u only need to put the values of the current conditions ur in for example in the scanner u need to log rpm, fuel rail pressure, timing adv, injectors pulse width those r ur inputs in the table i tried it and it works but i am have a c7 to try on if dave can supply one with 5.3 trucks modifiers it wld be great

  6. #6
    Senior Tuner Higgs Boson's Avatar
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    it doesn't work on all programs. i opened it up with excel just fine. i opened it in google docs and the #VALUE broken formulas showed up.

  7. #7
    Senior Tuner Ben Charles's Avatar
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    Good call Higgs, I will open it with Excel and see what I get.

    I have been looking at injection timing quite a bit, eager to see how this plays into what I have seen.

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  8. #8
    Quote Originally Posted by Ben Charles View Post
    Good call Higgs, I will open it with Excel and see what I get.

    I have been looking at injection timing quite a bit, eager to see how this plays into what I have seen.
    Ben i have been tuning 5.3 trucks boosted either turbos or superchargers i had luck with those tables by increasing them and this resulted on some trucks like 30-40whp difference however if u play with the wot variable cam advance and retard it through the whole thing out and needs to be retuned again....

    Plz if u have any findings update us

  9. #9
    Senior Tuner Higgs Boson's Avatar
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    So you are getting more power from SOI by increasing the values, which means starting injection sooner....where in the table are you increasing the values? They range from 275 to 345 (give or take) so are you making them all closer to 345 or what?

    The spreadsheet seems to indicate lowering the values.

  10. #10
    Senior Tuner DSteck's Avatar
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    The spreadsheet indicates the length of injection just to cover what you're trying to do. You can advance it further. Don't read too much into it.

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  11. #11
    Senior Tuner Ben Charles's Avatar
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    Ben i have been tuning 5.3 trucks boosted either turbos or superchargers i had luck with those tables by increasing them and this resulted on some trucks like 30-40whp difference
    I have not had a chance to mess with it as much as I want to, but I just don't see how LOWERING the values will help any. Increasing the values injects fuel sooner which gives a "longer injection window" One big shop in texas on the corvetteforum was mentioning how they were running out of fuel on a C7 Z06 at 675rwhp on pump gas. I can't confirm, but I am 99% sure they left the SOI table stock since a fiend of mine who actually knows how to tune made the same number on E85 .
    The way I base the SOI tuning is by looking at the camshaft and the IVO of the cam and starting injection around that DEGREE, the engine will let you know I your doing it correct by fuel pressure staying consistent (not dropping off) and no "Fuel knock" Most desensitize the Knock sensors, but if they mod the SOI table correctly they may not even have to do that or to a lesser degree.
    The Z06 numbers are far more aggressive than the C7.

    In the other thread about "injection Timing" I was going to post some graphs I made that show what I am about to mention. So without visual aid, hope this helps or makes sense.
    The C7 stock cam is 200/207 116.5 LSA (don't know if its advanced factory, so say intake centerline is straight up at 116.5, again VVT CAN/WILL COME INTO ACTION HERE)
    This means the stock cam
    IVO is -16.5 ATDC (normally cams are before BTDC, but factory cams are VERY SMALL)
    IVC is 36.5 ABDC
    EVO is 40.0 BBDC
    EVC is -13.0 BTDC
    So a 360 degree crank rotation shows the LT1 STOCK at WOT around 335, I say that number on a stock cam (centerline straight up) can be increased to around 343.5, but the exhaust Valve closes at 373 degrees, so technically between 343.5 and 373 injection could start

    NOW lets see what happens when you retard the camshaft say 6 degrees up top
    IVO is now -10.5 and EVC is -19 so essentially SOI can now be increased to 350 to 379 roughly. You can play with VVT throughout the entire RPM making changes.

    Stock C7 Z06 has SOI at WOT around 354
    Stock cam is 189/223 120 LSA (again centerline guessing straight up at 120LSA, again VVT changes this
    IVO is -25.5 ATDC
    IVC is 34.5 ABDC
    EVO is 51.5 BBDC
    EVC is -8.5 BTDC
    The ZO6 is injecting much earlier, there doing this for 2 reason I believe, 1 more fuel being injected and 2 to increase cylinder pressure to make more power for the given setup.
    Looking at injection they can inject anywhere up to 368.5 degrees with the cam straight up.

    IF anyone has any input, please share, this is what I cam up with doing some math and looking at the given values.

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  12. #12
    Senior Tuner Higgs Boson's Avatar
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    I still don't know what the point is of injecting later and not just injecting everything all the time at EVC.

  13. #13
    Senior Tuner DSteck's Avatar
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    Valve events have less to do with this on direct injection. The goal is to get the fuel to pool in the dish on the piston. There's a reason the factory doesn't set the entire SOI table to the same value.



    I'll say it once again, the point of this was to show people who are putting a huge demand on the system what the absolute latest SOI would be in order to actually have time to even complete the pulse.

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  14. #14
    Senior Tuner Higgs Boson's Avatar
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    So the SOI Max Angle is 350, what is the SOI Min Angle? There is no limit set in the tune, using the spreadsheet, I can inject fuel at idle at 23 degrees but that would be on the compression stroke. Obviously I could go try it but I have a lot of computer time Mon-Fri and not much car time.

    The spreadsheet says:
    Idle 25 deg
    WOT 200 deg

    Stock values are:
    Idle 310
    WOT 335
    (give or take)

    These values are much lower than the stock table, so I guess I am not taxing the fuel system....but I have to ask, why are they so much lower than stock values? Emissions?

    Steck, I appreciate the spreadsheet, but imagine giving a caveman a computer, he will just look at it and might eventually hit it with a rock. Can you offer any words of wisdom on how we can use this most effectively?

  15. #15
    Senior Tuner DSteck's Avatar
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    Again, SOI has more to do with getting fuel into the right spot of the piston at the right time. Period. End of story. Do not over complicate it by worrying about idle scenarios.

    This is only generally useful at WOT conditions that are at the end of the SOI table (1.36g/cyl column). Let's say you're at 10mPa rail pressure and 6800rpm. You can start playing with the injector pulse width to get an idea of what kind of SOI you need to even complete the cycle. For kicks, enter 9ms. That spits out a SOI of 386.7* and a cylinder load of 1.65g/cyl (assuming target AFR of 12.0).

    A factory LT1 table at 6800rpm and 1.36g/cyl (maxed) is only 332. The calculator is telling you that you need to advance SOI in order to even meet the requested demand.

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  16. #16
    Senior Tuner Higgs Boson's Avatar
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    Thank you that is helpful.

  17. #17
    Quote Originally Posted by Higgs Boson View Post
    Thank you that is helpful.
    Also wat i have noticed after u get the data in the SOI correct and then go retard the cam u start getting knock and misfire and it starts bucking and kicking.

    As Dave said the only area where u need to play is the right bottom side of the table at wot wat i do is log injector pulse width and see if it drops from the earlier run it means i am moving in the right direction. I will try to post some of the tunes i did so far 12 boosted trucks in total boosted with great results. Managed to make 540whp out of a 6.2 truck on a mustang dyno on 7psi another one i tuned without playing with those tables i barely hit the 500whp both had whipple 2.9

  18. #18
    Senior Tuner Ben Charles's Avatar
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    I will have excel tomorrow and will look at some of his, thanks again Dave (always helping)

    Jarrah if you want to post a tune that is fine. I wouldn't mind looking at it in regards to your SOI. I have not tuned a Boosted Gen 5 setup yet.

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  19. #19
    Senior Tuner mowton's Avatar
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    Its raining here today so I am playing with this. Thanks Dave for sharing yet another great tuning tool ...ur the man :-)

    Quick question or assumption. I believe the Fuel Rail Pressure input is coming from the Fuel System>General>Fuel Pressure>Desired table,. correct?

    Also the IFR multiplier and offset are parameters relative to the stock injectors and these values would change if you installed (or could find) new performance injectors. also correct?

    Thanks and have a great day...

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  20. #20
    Senior Tuner DSteck's Avatar
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    The fuel rail pressure comes from the scanner.

    Yes, the offsets and multipliers would change. I hid the cells where I convert those to an equation (offset is actually three equations because it doesn't follow an overall trend).

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