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Thread: ls1 big cam ignition timing

  1. #1
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    Default ls1 big cam ignition timing

    just wondering what sort of timing people are running with big cams. i have almost 70deg of overlap in a std stroke ls1 with 10.8:1 comp and mild ported heads 3k stall 3.9 diff gears atm timing is about 24 idle 45 at cruise 42 light acceleration 33 heavy acceleration and 29 at wot. there are no signs of knock retard and carnt hear any knock but i have no knock ears every time i add timing it get better to drive but without the correct tools for the job where do i stop.
    the reason i ask is i have payed 2 shops to tune this car both shop with a good rep and both times it has come back driving like shit even worse than the 30 min base tune i did on it to get it to the shop. so now i have decided to just do it myself but i am no tuner. anyone with any info please comment any help would be great

    forgot to mention i was using the dvt control while doing this log and have since updated my tune but have now found that it wont go over 40deg even if i command a higher number seems the limit of efi live is 40deg does anyone know if i am correct
    Last edited by h41ry; January 18th, 2017 at 01:10 AM.

  2. #2
    Joe (Moderator) joecar's Avatar
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    What is your cam's 0.050' specs (int/exh duration, lsa, installed advance)...?

    What heads do you have...?

    Post your tune file and some log files.


    If you have a lot of overlap (DCR is lower) you can get away with more timing, 29 degrees is ok, don't go higher.

  3. #3
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    Is there a general rule of thumb as to how the curve changes? Bring in more sooner, more overall, but maybe a dip in the middle if the cam really packs in that much more air and closes the intake valve 10 or so degrees sooner?
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  4. #4
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    cam is 233/242 110lsa 108icl installed at 0 no idea who did the heads but i had them flowed and checked the comp they flow 288cfm intake and 210 exhaust @ .600 lift. also has 1 7/8 4 into 1 headers
    this is a log i have just done i heard 2 small pings one was at wot about .88 at 4800 and the other was heavy load about .84 at 4400. it is showing a bit of knock retard today mostly when i back off and while the converter is locked im guessing that my knock sensors are accurate by the look of the table. it still feels like its lacking mid range and low-mid rpm wot it may be my mixtures?

    jon vz.ctzLog_0006.efi

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    i also did a tune that was richer at low rpm high load its was about 12.2 under 2800rpm 12.1 upto 3600rpm 12.7 upto 5200rpm and 12.8 the rest. it was hard to say if it was better but going off the calc torque pid it mad alot more torque but not sure how accurate that pid is and according to my spark plugs it was to rich. the current tune is 12.8 at wot the whole way through

  6. #6
    Joe (Moderator) joecar's Avatar
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    Your log shows you have too much timing at WOT/high load (32 degrees)...

    The LSx heads are designed to promote fast burn, so mid 30's timing (like SBC) willl actually hurt TQ (and the engine).

    I think you should be good with WOT timing at 27 degrees (unless you have dyno time to play with this to find best TQ wrt advance).


    I think you will be safer with commanded AFR set to 12.6 instead of 12.9+ (unless you have dyno time to play with this).

    I don't see the correct wideband pid in your log (EXT.WO2AFR1 is pegged at 25).

  7. #7
    Joe (Moderator) joecar's Avatar
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    Be careful if you run boost.

  8. #8
    Joe (Moderator) joecar's Avatar
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    Your HI and LO timing tables are too agressive... try the 2002 F-car tables.

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    thanks joecar after doing that log i have backed the timing off atm its 3-4 degrees less and it seems to be working well now showing almost no sign of kr once i eliminate that i will back it off a little more to be safe. but still playing with the mid to hard acceleration area may need to drop it some more. the w02 pid works the wideband is currently in another car so i carnt do much with the wot until i get is back. by the look of my spark plugs mid range was to rich so i tried running in closed loop until 80kpa and its now also driving much better.
    atm the car is aspirated but once the tune is done i have a nitrous kit to go on her but i will be saving that until it goes on the dyno i plan on running a 150 shot so hopefully it will run a high 10.
    since the 1mb pcm has not got the n20 feature in the operating system i havent looked into it yet but woould it be possible to use wire up the activation to the egr output of the pcm and use the egr timing map to retard the timing?

  10. #10
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    Quote Originally Posted by joecar View Post
    Your log shows you have too much timing at WOT/high load (32 degrees)...

    The LSx heads are designed to promote fast burn, so mid 30's timing (like SBC) willl actually hurt TQ (and the engine).

    I think you should be good with WOT timing at 27 degrees (unless you have dyno time to play with this to find best TQ wrt advance).


    I think you will be safer with commanded AFR set to 12.6 instead of 12.9+ (unless you have dyno time to play with this).

    I don't see the correct wideband pid in your log (EXT.WO2AFR1 is pegged at 25).
    How about low RPM, i.e. cruising in 6th. Would it want more than stock there? I'm thinking RPM lower than where effective scavenging begins to take place. In my mind cylinder pressures would be lower than stock there, right? ICL may be something like 12 degrees sooner, but the cam has damn near 30 degrees more duration @.050" (depending on the year) with a narrower LSA so lots more overlap.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

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