Results 1 to 10 of 10

Thread: Advance from RPM max question

  1. #1
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
    Join Date
    Mar 2006
    Location
    Albany Wisconsin
    Posts
    722

    Advance from RPM max question

    I noticed that in a tune that I have that is NOT a turbonator tune, advance from rpm max graph line starts out at low rpm with high advance, for example 900 rpm might be at 54 degrees and 7000 rpm might be 39 degrees with advance decreasing as rpm increases. In turbonator tunes timing goes in the opposite direction, 900 rpm would be 28 degrees 5000 rpm might be 49 degree's. Can someone explain this?
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  2. #2
    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
    Join Date
    Dec 2005
    Location
    Warsaw, NY
    Posts
    8,324

    Re: Advance from RPM max question

    your tables are from a 89 2.5 t1. look at those cals if you wanna compare. there are no 87 2.5 Turbo cals so to make a 87 LM 2.5 cal, 89 2.5 tables were copied in.

    Brian

    Quote Originally Posted by turbovanman
    This one is easy, I have myself to blame, I rush things, don't pay attention to gauges when I should, change to much stuff at once then expect miracles, the list is endless.

  3. #3
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
    Join Date
    Mar 2006
    Location
    Albany Wisconsin
    Posts
    722

    Re: Advance from RPM max question

    Brian, that is a surprise, that would never have occurred to me. In the knowledge center, shelgame talks about total timing being calculated by adding basic timing + advance from RPM + Advance from map. He then later says there is no such thing as basic timing. That causes me to ask which of the formula's below would give the correct answer to your total timing at any given point. I am using representative numbers.
    basic timing = 12 degrees + advance from rpms 30 degrees + Advance from map -20 degrees. 12 + 30 + -20 = + 22 degree total advance, OR...
    basic timing = 0 degrees + advance from rpms 30 degrees + Advance from map -20 degrees. 0 + 30 + -20 = + 10 degrees total advance
    Last edited by jeff1234; 07-05-2019 at 11:59 PM.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  4. #4
    Supporting Member II Turbo Mopar Contributor
    Join Date
    Feb 2015
    Location
    toronto
    Posts
    1,007

    Re: Advance from RPM max question

    IIRC,Shelgame was trying to get the reader to understand that there is no base timing. We do not have a crank sensor so the ECU does not know where TDC is. All it knows is the position of the dizzy, and the cutout in one of the flags identifies which cylinder is which via the HEPs. All timing are relative to the position of the distributor, this position maybe or may not be 12 BTDC.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  5. #5
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
    Join Date
    Mar 2006
    Location
    Albany Wisconsin
    Posts
    722

    Re: Advance from RPM max question

    I don't know what IIRC means. All I want to do is calculate actual timing at any given point in advancefrommapwarmfull.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  6. #6
    Supporting Member II Turbo Mopar Contributor
    Join Date
    Feb 2015
    Location
    toronto
    Posts
    1,007

    Re: Advance from RPM max question

    IIRC--If I recall correctly...
    I have not determined timing values myself so I will refer to those in the know.
    Rob does say


    Q - How is the total timing calculated? Base timing + AdvancefromRPM + AdvancefromMap?

    A – There is no such thing as ‘base timing’. Total timing is pretty simple – Advance from RPM + Advance from MAP is the basic timing. The advance from MAP can be either the WOT or P/T table depending on TPS position. And, there is a WOT multiplier for the advance from MAP table for when the lookup value from that table is negative. There is also a maximum timing value.


    Q - So I am clear on this.... The timing shown in the cal, and on a Scan Tool, will be the total timing. This number assumes the base timing of 12* (or whatever is called for on the emissions label) is there. So the number shown in a cal is not necessarily the number used in a calculation, correct?

    A - There is no such thing as ‘base timing’. The 12* is just the fixed timing used to set the sync between the distributor and the crank. The reason they chose 12* is simply because an engine generally will not run well @ 0* advance. The 12* is not a 'base' timing at all. It's simply a reference point. It never gets 'added' to anything. All the timing figures in the cal are relative to TDC (0*).

    If the sync is in fact wrong (ie, you set the sync at 14* instead of 12*), then the actual timing will be off by the same amount (2* in this example). But, the ECU will not know about that difference and will not be able to report it to a scan tool.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  7. #7
    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
    Join Date
    Dec 2005
    Location
    Warsaw, NY
    Posts
    8,324

    Re: Advance from RPM max question

    Quote Originally Posted by jeff
    basic timing = 0 degrees + advance from rpms 30 degrees + Advance from map -20 degrees. 0 + 30 + -20 = + 10 degrees total advance
    This.

    Quote Originally Posted by turbovanman
    This one is easy, I have myself to blame, I rush things, don't pay attention to gauges when I should, change to much stuff at once then expect miracles, the list is endless.

  8. #8
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
    Join Date
    Mar 2006
    Location
    Albany Wisconsin
    Posts
    722

    Re: Advance from RPM max question

    Thanks Miles, I have read this info in the knowledge center.
    Jeff
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  9. #9
    Supporting Member II Turbo Mopar Contributor
    Join Date
    Feb 2015
    Location
    toronto
    Posts
    1,007

    Re: Advance from RPM max question

    Quote Originally Posted by Aries_Turbo View Post
    This.
    Good, this is consistent with my understanding
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  10. #10
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
    Join Date
    Mar 2006
    Location
    Albany Wisconsin
    Posts
    722

    Re: Advance from RPM max question

    Thanks Brian, I suspected that this would be the correct formula.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

Similar Threads

  1. advance from rpm max vs advance from map warm full
    By jeff1234 in forum Electrical & Fuel System
    Replies: 18
    Last Post: 03-27-2018, 10:27 PM
  2. Advance from rpm max
    By jeff1234 in forum Electrical & Fuel System
    Replies: 34
    Last Post: 09-05-2017, 10:39 AM
  3. Limit for Hot Map Advance
    By turbo84voyager in forum EFI Tuning
    Replies: 1
    Last Post: 08-12-2014, 11:52 PM
  4. smec cal mechanical spark advance question
    By Joe_Van_Duno in forum EFI Tuning
    Replies: 4
    Last Post: 06-26-2014, 03:28 PM
  5. Replies: 12
    Last Post: 07-24-2010, 02:44 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •