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Thread: Injector Timing? Reference Periods? refereencing what?

  1. #21
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by MikeGyver View Post
    I don't get it. It is desirable to spray the injector only when the valve is closed? ...(?)!
    From the factory, as I was told, GM tries to spary the back side of the closed intake valve... which aids in evaporation and keeps you from hosing down the cylinder walls...
    too far early and you puddle up, too late and you wash the cylinder walls and rings down with fuel...
    Just right and the heat helps with fuel evaporation, and allows it to all burn just right.

    My thought would be just to follow GM's practice.. move back the injector timing to shoot for the back of the valve still...


    I may get time to play with how it works on the dyno tomorrow with a customers car., no guarantees... I'm still trying to find out for sure if the guy wants me to tune his vette tomorrow or to wait till next week
    -Scott -

  2. #22
    Advanced Tuner MikeGyver's Avatar
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    Huh. I always thought that "spraying the back of the valve" just meant that the injector sprays the back of the (open) valve.
    Can you explain why less fuel would go out the exhaust at low engine speeds, to make less fuel smell at idle, like I read in other posts?
    2000 GMC 2500 2-bar SD
    Stock LM7, LTs, TBSS intake manifold

  3. #23
    Senior Tuner LSxpwrdZ's Avatar
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    The problem is larger cam's have more overlap and the instant opening of the intake valve has the exhaust still open and usually this will cause that evaporated atomized fuel mixture to shoot right out the exhaust valve. My personal preference for larger overlap cam's is to delay the injection to a later time so that the exhaust valve is closed before the injection stops.

    I can see some of the cylinder wall wash but if you really think about it the air velocity in the port is so great that I don't see this being much of an issue unless you are just running the thing pig pig rich or injecting way way late in the cycle.

    The calculation is the end of injection. Using stock numbers that put's it around 300* which would make sense because the injector fires on the back of a closed valve.
    Last edited by LSxpwrdZ; 01-04-2011 at 12:49 PM.
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  4. #24
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by LSxpwrdZ View Post
    The problem is larger cam's have more overlap and the instant opening of the intake valve has the exhaust still open and usually this will cause that evaporated atomized fuel mixture to shoot right out the exhaust valve. My personal preverence for larger overlap cam's is to delay the injection to a later time so that the exhaust valve is closed before the injection starting point occurs.

    I can see some of the cylinder wall wash but if you really think about it the air velocity in the port is so great that I don't see this being much of an issue unless you are just running the thing pig pig rich or injecting way way late in the cycle.

    The calculation is the end of injection. Using stock numbers that put's it around 300* which would make sense because the injector fires on the back of a closed valve.
    by that thought...
    My cam as the example again

    stock exhaust valve = 348*
    my cam exhaust valve = 367*
    so move it 19* Later
    19/90 = 0.21 later
    -Scott -

  5. #25
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    With the info below how do I find what degree the event occurs?

    VALVE OPEN INTAKE 9 BTDC
    VALVE OPEN EXHAUST 54 BBDC
    VALVE CLOSED INTAKE 47 ABDC
    VALVE CLOSED EXHAUST 8 ATDC

  6. #26
    Advanced Tuner MikeGyver's Avatar
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    Quote Originally Posted by soundengineer View Post
    by that thought...
    *
    so move it 19* Later
    ...
    By that thought... at 900 rpm, 19° takes .0035 second. How long is your injector open at idle?
    2000 GMC 2500 2-bar SD
    Stock LM7, LTs, TBSS intake manifold

  7. #27
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by LS1Vette View Post
    With the info below how do I find what degree the event occurs?

    VALVE OPEN INTAKE 9 BTDC
    VALVE OPEN EXHAUST 54 BBDC
    VALVE CLOSED INTAKE 47 ABDC
    VALVE CLOSED EXHAUST 8 ATDC

    360* is TDC between Valve events
    BDC for Exhaust stroke is 180*
    BDC for Intake Stroke is 540*

    IVO = 351
    EVO = 126
    IVC = 587
    EVC = 368

    you have a 236/242 111LSA+2
    Last edited by S2H; 01-03-2011 at 09:47 PM.
    -Scott -

  8. #28
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by MikeGyver View Post
    By that thought... at 900 rpm, 19° takes .0035 second. How long is your injector open at idle?
    the PCM backfigures how long the injector should be open and when it should open
    I dont care how long the injector takes.... I just want the maximum finish time delayed by that many degrees
    and I am using a GM OEM injector from an ASA car... so I have all my offset and injector tables populated by GM data
    -Scott -

  9. #29
    Advanced Tuner MikeGyver's Avatar
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    My point is that if you want the injector to start after the exhaust valve closes (I think I do), you would need to know how long the injector is open.
    2000 GMC 2500 2-bar SD
    Stock LM7, LTs, TBSS intake manifold

  10. #30
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by MikeGyver View Post
    My point is that if you want the injector to start after the exhaust valve closes (I think I do), you would need to know how long the injector is open.

    at that rpm its down around 2ms pulse width...
    again...its back figured to hit the End of Injection Target..
    so we think of it as where it fires in relation the the intake side...
    Exhaust valve closes at 347ish...
    the EIOT is at 300ish
    I wouldnt think you could benefit from making it that late in the fire to make it spray after the exhaust valve closes..that would be way late for a large cam...you're talking about having to move it 50+ degrees at that point...
    -Scott -

  11. #31
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    Quote Originally Posted by soundengineer View Post
    360* is TDC between Valve events
    BDC for Exhaust stroke is 180*
    BDC for Intake Stroke is 540*

    IVO = 351
    EVO = 126
    IVC = 587
    EVC = 368

    you have a 236/242 111LSA+2
    That's exactly what I have.

    Okay I think I've got it.

    IVO = 351 + 9 = 360 BTDC
    EVO = 126 + 54 = 180 BBDC
    IVC = 587 - 47 = 540 ABDC
    EVC = 368 - 8 = 360 ATDC

    How did you figure out my duration/lift and LSA +2 degrees?

    So my LS6 cam ivo is 379 so that a difference of 28*. 28/90 = .31

    So move the timing up .31 correct?
    Last edited by SargeZ06; 01-03-2011 at 10:13 PM.

  12. #32
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by LS1Vette View Post
    That's exactly what I have.

    Okay I think I've got it.

    IVO = 351 + 9 = 360 BTDC
    EVO = 126 + 54 = 180 BBDC
    IVC = 587 - 47 = 540 ABDC
    EVC = 368 - 8 = 360 ATDC

    How did you figure out my duration/lift and LSA +2 degrees?
    valve events + more math get me durations, intake centerline, exhaust centerline, which comes up to LSA as well

    IVC-IVO = 587-351 = 236
    EVC-EVO = 368-126 = 242
    (IVO+IVC)/2 = 469 = (469-360 = 109) 109 ICL
    (EVO+EVC)/2 = 247 = (360-247= 113) = 113 ECL
    109+113 /2 = 111 LSA and the 109ICL makes it +2
    -Scott -

  13. #33
    Senior Tuner LSxpwrdZ's Avatar
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    Yeah I worded that wrong earlier about starting the pulse after the exhaust valve closes. That is too late. Finding the sweet spot in that overlap is key because the overlap acts like a vacuum on the exhaust side with all the exhaust gasses speeding out the header. So catching the tail end of that velocity is key. Also remember the .050" numbers aren't when the valve is physically closed. They are still open for a little duration past that. So with that said I still like to delay it as much as possible so that there is still being a little bit of pulsewidth with the exhaust fully closed.
    James Short - [email protected]
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  14. #34
    Advanced Tuner MikeGyver's Avatar
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    Quote Originally Posted by soundengineer View Post
    ...
    I wouldnt think you could benefit from making it that late in the fire to make it spray after the exhaust valve closes ...
    I guess I am just wishing we had direct injection.
    2000 GMC 2500 2-bar SD
    Stock LM7, LTs, TBSS intake manifold

  15. #35
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by LSxpwrdZ View Post
    Yeah I worded that wrong earlier about starting the pulse after the exhaust valve closes. That is too late. Finding the sweet spot in that overlap is key because the overlap acts like a vacuum on the exhaust side with all the exhaust gasses speeding out the header. So catching the tail end of that velocity is key. Also remember the .050" numbers aren't when the valve is physically closed. They are still open for a little duration past that. So with that said I still like to delay it as much as possible so that there is still being a little bit of pulsewidth with the exhaust fully closed.

    unfortunately I dont know the @.006 for the stock LS1 cam...
    I know my cam specific valve events for .006 and .050
    so I went off of .050 since thats what I know for the stock cam

    the majority of our aftermarket cams have about 25* between .006 and .050
    give or take a few depending on the lobe

    even then, its still quite a ways from 300 and even further for the exhaust valve closing..


    the ideal is that velocity point...which I'm sure with some serious math that I dont feel like diving into, could be calculated for a new cam.
    but I'm not about to dive into a 3 week design in Matlab just to come up with something I may be able to test on a dyno sometime soon..LOL


    theres no overlap in the stock cam....so theres no velocity benefit from the exhaust... they are basing all of their velocity on the opening of the intake valve on the stock LS1 cam

    by that logic... why not get the same or similar velocity from backing up the timing and making it fire sooner with a larger cam

    with the overlap, you will get some reversion, so you potentially could keep some fuel by spraying it on the back of the valve as opposed to inside the cylinder
    -Scott -

  16. #36
    Senior Tuner S2H's Avatar
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    and because I'm a nice guy...

    some basic Camshaft Math

    Valve Events to Duration or Duration to Valve events
    -Scott -

  17. #37
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    Quote Originally Posted by soundengineer View Post
    unfortunately I dont know the @.006 for the stock LS1 cam...
    I have it for the LS1 and LS6 @.004


    PRODUCTION 2002 LS6 5.7L CAMSHAFT.
    117.5 LDA 120 INTAKE CENTERLINE.
    1.70 ROCKER RATIO
    Lift:
    @Cam @Valve
    EXHAUST: 0.322 0.548
    INTAKE: 0.324 0.551

    Cam [email protected] Tappet Lift:
    Open Close Adv. Duration
    EXHAUST: 69 BBDC 33 ATDC 282
    INTAKE: 7 BTDC 80 ABDC 267

    Cam [email protected] Tappet Lift:
    Open Close Duration
    EXHAUST: 42 BBDC 4 BTDC 218
    INTAKE: 19 ATDC 43 ABDC 204






    116 LDA 115 INTAKE CENTERLINE.
    PRODUCTION 2001 6.0L TRUCK AND 5.7L
    LS1 CAR CAMSHAFT.
    1.7 ROCKER RATIO
    Lift:
    @Cam @Valve
    EXHAUST: 0.281 0.475
    INTAKE: 0.274 0.463

    Cam [email protected] Tappet Lift:
    Open Close Adv. Duration
    EXHAUST: 71 BBDC 33 ATDC 284
    INTAKE: 11 BTDC 87 ABDC 278

    Cam [email protected] Tappet Lift:
    Open Close Duration
    EXHAUST: 39 BBDC 12 BTDC 207
    INTAKE: 17 ATDC 33 ABDC 196

  18. #38
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    There has got to be more to the formula. If you use Bluecats equation everything looks plausible when ECT is at operating temp. What about when ECT is @ 68, the number comes back @ 30.570317.

    Makeup must have some influence on it. Need to instrument a running motor and see how changing the numbers influences the injector start pluse....

  19. #39
    Senior Tuner S2H's Avatar
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    Quote Originally Posted by LS1Vette View Post
    I have it for the LS1 and LS6 @.004


    PRODUCTION 2002 LS6 5.7L CAMSHAFT.
    117.5 LDA 120 INTAKE CENTERLINE.
    1.70 ROCKER RATIO
    Lift:
    @Cam @Valve
    EXHAUST: 0.322 0.548
    INTAKE: 0.324 0.551

    Cam [email protected] Tappet Lift:
    Open Close Adv. Duration
    EXHAUST: 69 BBDC 33 ATDC 282
    INTAKE: 7 BTDC 80 ABDC 267

    Cam [email protected] Tappet Lift:
    Open Close Duration
    EXHAUST: 42 BBDC -4 ATDC 218
    INTAKE: -19 BTDC 43 ABDC 204






    116 LDA 115 INTAKE CENTERLINE.
    PRODUCTION 2001 6.0L TRUCK AND 5.7L
    LS1 CAR CAMSHAFT.
    1.7 ROCKER RATIO
    Lift:
    @Cam @Valve
    EXHAUST: 0.281 0.475
    INTAKE: 0.274 0.463

    Cam [email protected] Tappet Lift:
    Open Close Adv. Duration
    EXHAUST: 71 BBDC 33 ATDC 284
    INTAKE: 11 BTDC 87 ABDC 278

    Cam [email protected] Tappet Lift:
    Open Close Duration
    EXHAUST: 39 BBDC -12 ATDC 207
    INTAKE: -17 BTDC 33 ABDC 196
    gotta be careful when reading these...
    BTDC is negative values when you put it to ATDC and vice versa....

    should always post them the same when you show a .006 and a .050
    -Scott -

  20. #40
    Senior Tuner S2H's Avatar
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    and your #'s for seat to seat valve events must be wrong for the LS1 cam...
    because math doesnt lie and you would have 2 different centerlines from those valve events

    for the LS1 Cam...I get that valve events should be
    Exhaust 74.5 / 23.5
    Intake 27 / 77
    Last edited by S2H; 01-04-2011 at 08:42 AM.
    -Scott -