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Thread: Help me understand cam timing (LNF)

  1. #1
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    Question Help me understand cam timing (LNF)

    I'm looking a the main exhaust and intake cam angles (warm), and in the exhaust table the values are positive, advance right? In the intake table, the values are negative, retard right?

    So the intake valves are opening later in the combustion cycle and the exhaust valves are opening sooner in the combustion cycle. This ultimately means less overlap right?
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

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    That's somethign that has been pretty foggy so far. Noone can definitivly say what the units are with repect to.
    Me love boost long time.

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    Quote Originally Posted by oldskool View Post
    So the intake valves are opening later in the combustion cycle and the exhaust valves are opening sooner in the combustion cycle. This ultimately means less overlap right?
    I think its the other way around, intake cam gets advanced and exhaust one gets retarded. The lnf runs a lot of overlap.

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    so the units are backwards in the tables? positive is retard and negative is advance?
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

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    How are people adjusting these tables without definately knowing the units? In HPT it says the units are degrees, but allows for some crazy large number of +/-.

    Maybe one of the HPT guys can weigh in here? I'd be happy for now knowing what sign (+/-) goes with advance or retard.

    And, shabby, i though a lot of overlap was not good for turbocharged engines? Blowthrough or something like that?

    My theoretical would be what if you set all the main intake and exhaust values to zero? would this be basically running the stock overlap specs on the cams?
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

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    Quote Originally Posted by oldskool View Post
    I'm looking a the main exhaust and intake cam angles (warm), and in the exhaust table the values are positive, advance right? In the intake table, the values are negative, retard right?

    So the intake valves are opening later in the combustion cycle and the exhaust valves are opening sooner in the combustion cycle. This ultimately means less overlap right?
    You have the correct concept, just don't get confused by advance or retard terminology. Larger negative means opening sooner, which is commonly referred to as advancing the cam. Larger positive means opening later, or commonly referred to as retarding the cam. It is the same on both cams, just that the exhaust opens before bottom dead center and the intake opens before top dead center. You want to reduce overlap at higher rpm and retard the intake cam to maximize cylinder fill volume. In midrange the overlap is increased for emissions purposes to reduce N0x. Overlap is reduced at idle for smooth idle. Emissions requirements compete with performance requirements, your objectives may be different for a race tune than for a street tune that needs to meet emission requirements.

    Cheers,
    VTuner

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    It's (overlap) is also used down low to keep the stock turbo out of the surge window.

    I beleive the LNF is a clearance motor so you can run any cam timing you want without clash.
    Me love boost long time.

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    Thumbs up

    Quote Originally Posted by VTuner View Post
    You have the correct concept, just don't get confused by advance or retard terminology. Larger negative means opening sooner, which is commonly referred to as advancing the cam. Larger positive means opening later, or commonly referred to as retarding the cam. It is the same on both cams, just that the exhaust opens before bottom dead center and the intake opens before top dead center. You want to reduce overlap at higher rpm and retard the intake cam to maximize cylinder fill volume. In midrange the overlap is increased for emissions purposes to reduce N0x. Overlap is reduced at idle for smooth idle. Emissions requirements compete with performance requirements, your objectives may be different for a race tune than for a street tune that needs to meet emission requirements.

    Cheers,
    VTuner
    Thank you, this is what i was looking for. Do you mind me asking how/where you came across this info? I would intuitively think (-) is retard, but appears not to be the case...



    Quote Originally Posted by Baldturbofreak.com View Post
    It's (overlap) is also used down low to keep the stock turbo out of the surge window.

    I beleive the LNF is a clearance motor so you can run any cam timing you want without clash.
    This is also good to know, but there are timing values/combinations that will cause it to run like crap right?
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

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    More food for thought - I've read that the cam timing on the LNF is adjustable +/- 25* for each camshaft indepenently. I cannot find the source right now, but i remember the numbers. You notice that the value limits for the cam tables in HPT are +/- 256*. Could every ten units in HPT be equal to about 1 degree of cam timing? (every HPT unit is about one tenth of a degree?). I'm also assuming this is relative to crankshaft position, TDC right?

    Just so you guys know, i'm not changing these tables yet, lol, i really want to understand what and why first.
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

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    I have had luck adding to the Main Intake cam table by a little bit.

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    Quote Originally Posted by oldskool View Post
    I would intuitively think (-) is retard, but appears not to be the case...

    ?
    I think being negative is retarded too. So unproductive

    too much overlap down low= no power.
    Not enough up top= no power.
    Me love boost long time.

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    Ok, could someone look at the attached spreadsheet, mainly the section in red text. Does this make sense, and is it theoretically correct if you assume the vaules in the HPT cam tables are one tenth of a cam degree?

    I want to be able to quantify the overlap in any given cell to make adjustments that mean something to me.

    Thanks to the pro's here for your help/advice.
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

  13. #13
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    Overlap calculations require lift and duration of both intake and exhaust cams. Greg Banish can be found on this forum and his books are a great resource. For now, try this link and downloads:

    http://www.compcams.com/Technical/TimingTutorial/

    Quote Originally Posted by oldskool View Post
    Ok, could someone look at the attached spreadsheet, mainly the section in red text. Does this make sense, and is it theoretically correct if you assume the vaules in the HPT cam tables are one tenth of a cam degree?

    I want to be able to quantify the overlap in any given cell to make adjustments that mean something to me.

    Thanks to the pro's here for your help/advice.

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    Thanks, that was a good read. Its a lot to digest . In the spreadsheed i was just trying to put the intake table and exhaust table together to illustrate how they are affecting overlap as a whole.

    OK now im looking at the cam angles in the scanner and they do not seem to match whats in the cam tables. The entire intake cam angle (warm) table is negative, but the observed angle in the scanner is almost never negative ?? How does this work?
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

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    I always assumed it was jsut a unit error in the scanner.
    Me love boost long time.

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    Quote Originally Posted by Baldturbofreak.com View Post
    I always assumed it was jsut a unit error in the scanner.
    Guess I should check this with a Tech 2 eh? I'll get right on that
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    Quote Originally Posted by Baldturbofreak.com View Post
    I always assumed it was jsut a unit error in the scanner.

    This sounds like a reasonable assumption.
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

  18. #18
    I have also been fighting with myself trying to understand these cam tables. a tuner on another from seems to think my pte5457 swapped lnf cobalt should be spooling a .63 a/r faster than 4500rpm for full boost.... here is what I know thus far:

    for every 10 "points" worth of change is = to 1 cam degree.
    I have found by setting the intake cam table to an additional -20 points (-2 degrees of cam timing) the car runs no diff and it will throw a p0011 dtc. which is a intake cam to far advanced.

    so the more negative the number the more advanced the cam is according to the dtc.
    the car didn't go into limp mode or anything just had a cel.
    now that we know negative means advance and positive means retarded in relation to tdc. what should one do to spool a larger turbo in regards to cam, a/f and ignition timing

    I was told open the intake sooner and exhaust sooner. this does nothing for my spool...
    I did -20 intake and -20 exhaust with no change....

  19. #19
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    The wierd thing is my RPD in my Cobalt shows values from 0-60 for cam advance :\
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    2012 Jeep SRT8
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    2013 XTS4 Custom IPC/BCM/CUE Auto High Beams
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  20. #20
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    Wow two additional degrees was enough to throw a code - why have +/- 25* adjustment if it's going to throw codes? What was the maximum value in the table? I understand if you don't want to post up a tune file, but it would be helpful.

    As far as spool up, i know hotter exhaust (and hence faster moving) is going to get you a quicker spool. Maybe you could retard timing in small amounts around your boost threshold (keeping in mind that we have main spark tables referenced to cam position). and see what it does for spool up?

    I read a lot of your post on CSS.net. It's good you came here becuase there is less BS - and a lot less people trying to convince you that they know all about tuning.
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq