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Thread: injector Timing {B3702}.... when to tune?

  1. #1
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    Default injector Timing {B3702}.... when to tune?

    I have been tuning my idle and VE since a recent cam upgrade in my 383. I went to a much more agressive cam and am running lucas 42# injctors. I have noticed that peopler rarely if ever, change the timing offset in B3702. I know the injector timing is an offset in the injector firing based on crank-based triggers.

    My question is... is this a constant with all LS1's for example? Let's say you increase stroke and then increase cam duration, and even have some cam advance ground in... shouldnt the injector timing be altered to better match the earlier opening of the intake valve?

    I am going to try and play with this... but I dont know what to watch or log to see the effects.... maybe AFR? Richer means a more complete burn?

    I am open to suggestions.

    2002 WS6, All-Lunati 383 Strok'r @11:1, Cartek Heads, Keith/Ross Racing Custom Cam, Victor Jr., 492whp 457wtq,
    Cartek Clutch, 9" Moser w/4.11's, 35 spline Detroit Locker, QA1's, NX, BMR, Tuned w/ EFILive V2 Black Box Logging
    Check Out My Latest Tune File: HERE

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    Lifetime Member SSpdDmon's Avatar
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    Quote Originally Posted by Goldfinger911 View Post
    I have been tuning my idle and VE since a recent cam upgrade in my 383. I went to a much more agressive cam and am running lucas 42# injctors. I have noticed that peopler rarely if ever, change the timing offset in B3702. I know the injector timing is an offset in the injector firing based on crank-based triggers.

    My question is... is this a constant with all LS1's for example? Let's say you increase stroke and then increase cam duration, and even have some cam advance ground in... shouldnt the injector timing be altered to better match the earlier opening of the intake valve?

    I am going to try and play with this... but I dont know what to watch or log to see the effects.... maybe AFR? Richer means a more complete burn?

    I am open to suggestions.
    Learn how to read your spark plugs...


    Then, teach me. LOL

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    I know how to read the plugs. The plugs are actually perfect when inspected. I am just always in search for perfection.

    I will be sure and let everyone know what I learn. I am trying to find a way to create a calc PID that will do variance. That will help with tuning for various types of stability. I start geeking out on this stuff and cant stop. Hahahaha

  4. #4
    Lifetime Member SSpdDmon's Avatar
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    Just thinking out loud here....

    But, if you have a cam with greater duration and let's assume some overlap....is it really going to net you anything to squirt the injector a little sooner? Wouldn't you just be shooting more unburnt fuel into the exhaust?

    IMO - messing with this table is not necessary for 95+% of the people that tune their own setup. Unless your injectors are static @ WOT, I don't know if you're going to see any significant gains. And if your injectors are static, you've got IDC problems to worry more about than simply when they're firing.

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    Yeah. You're probably right. I just got hooked on the idea that cam advance would equate to a change in injector firing to optimize the intake stroke efficiency. Originally my thought process was...

    -1 RPM = 360deg crank rotation
    -1000rpm = 360000 deg <---- typical big cam idle and to keep the math easy
    -16.67 revolitions per second
    -6000 degrees of rotation per sec
    -0.0167 revs per ms
    -6 degrees of rotation per ms
    -Therefore when advancing the intake opening event by 2 deg, this means firing the injector .334 ms sooner.

    But, once you factor in LSA and possibly a different ICL, the point becomes moot, I think.

    Oh well. Hahahaha. The exercise was fun.

    I wondering one more thing.... why... in the stock settings for Injector timing... does the timing offset increase with engine temp? Why would a hot engine need the injector fired sooner than a cold engine? (I am pretty sure the timing offset, it a time "in advance" to compensate for injector lag when fired.) Or.. is a time value AFTER the crank trigger? Hmmm... no must be an advance. to compensate for lag.
    Last edited by Goldfinger911; October 17th, 2008 at 07:01 AM.

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    Ok... um... I know i shouldnt But I have to post my results. <<GEEK ALERT GEEK ALERT>>

    I went back and retested before and after and came up with the same results. I flly warmed up my car to 80*c. I monitored AFR using a gauge on the dash page... because you can enable the min and max needles. With the stock injector timing settings, copied from the stock 20002 FBody LS1 tune, my AFRs bounced around at idle (like they always have) from anywhere between 13.8 to 15.8, giving me an average right about where it should be. I then used my logic above, and altered the timing to essentially fired the injector earlier. I subtracted.334ms from the injector timing because this equates to 2 degrees on the crank. I reflashed and restarted the car. I let it get to 80*c again and started my monitoring. Now, my AFRs bounce between 14.2 and 14.8. I thought I was seeing things, so I put the setitngs back and tested again... back to the way it was. Readded timing to the offset of .334ms and sure enough the AFR's are back to 14.2-14.8.

    Hmm... it occurred to me that that 2 degrees on the crank is 1 degree on the cam, the injectors are fired off the crank sensor, so I should actually use more time... so for the hell of it I am going to try to add .668ms and see what happens. I really dont have an explanation.. but I thought I would share. My cam specs are 242/248 .613"/.617" 112+2. This cam with my 11:1 (or higher) compression ratio makes for a rough idle.

    UPDATE: I tried lowering the timing offset by another .334ms and see the same result. Maybe slightly more stability but still definitely different that stock timing. Just to make sure, I put stock timings back again and saw the same bouncier AFRs. It is a good Friday.
    Last edited by Goldfinger911; October 17th, 2008 at 09:10 AM.

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    Lifetime Member swingtan's Avatar
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    Here's a few things I've seen with altering the Injector timing.....

    • With the E38, the stock timing is very high. 220' at normal operating temps and more when cold. I found that at times, fuel laden intake charge could be pulsed right out of the intake and result in a strong fuel smell inside the car.
    • Dropping the timing to a little under half the stock values removed the occasional fuel smell and altered the note and feel of the motor. It actually felt a little stronger.
    • Dropping the timing even further resulted in hesitations at idle if you stabbed at the throttle. I think the injectors were simply firing too late and resulted in a lean spike.
    • Altering the Injection timing a fair amount will mean you need to adjust the transient fueling as the to seem to go hand in hand. You may also need to revisit the VE table.


    Simon.

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    Thanks Swing'
    Those are awesome observations. I have idled my car and drove it some with my changes... and I actually do have less fuel smell both in the car and in the garage when idling to fully warm. (I always warm it up good before taking off.)

    I just found it funny that in almost all the idle and injection troubleshooting threads, no one mentions the injection timing. People always focused on the pulse width(s) and adders.

    I came from the AEM world... and on an AEM ECM, even the plug and play ones, injection timing is HUGE in tuning a car with bigger injectiors.

    I had 84lb Delphi injectors with twin Walbros, feeding a 2JZGTE (a whopping 183 cubic inches), with a set of mid sized Crower cams, and it idled smooth as glass at 14.6:1 AFR. I just think that there HAS to be more to the black art of LSx injection.

    Thanks man.
    Last edited by Goldfinger911; October 17th, 2008 at 03:30 PM.

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    Senior Member Sid447's Avatar
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    Agree with your yearning to understand Goldfinger911,

    As an aside LS Injectors fire when the IV is closed, am I correct?

    We could sure do with someone like David Vizard around here.

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    Hi Sid,

    Yeah man, I yearn to understand on a daily basis. Hahaha.

    If by IV you mean Intake Valve, then I think so. I think the injector firing coinsides with the instant before opening of the intake valve. Ideally, you would want it to fire with a low manifold pressure, maintain atomization, then fully ingest the fuel and air mixture, right? I am guessing here, and thinking outloud. If thats the case... and you have a cam that had advance ground in... then that intake valve is opening sooner... and you should ideally fire that injector sooner for optimal fueling?

    Now, if we could only find out when, with respect to TDC, a stock LS1 injector pulse happens.... Hmmm... Maybe the base pulse is actually at TDC, and the timing in the stock tune advances it. So, if the stock injection timing is 5.55ms. then that would be 33.3 degrees BTDC when fully warm?

    If thats the case... if I set my timing to zero.. then would fire at TDC? Hmmm.

    Off topic... I found a great source for injector info: http://users.erols.com/srweiss/tableifc.htm
    Last edited by Goldfinger911; October 17th, 2008 at 04:58 PM.

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