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Thread: Need Spark Advance help on L31 TPI engine

  1. #1
    Fuel Injected! darbysan's Avatar
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    Need Spark Advance help on L31 TPI engine

    I have a crate L31 ( Vortec Head 350) with TPI induction, running on ARAP bin with 1227165 ECM. I've been running for years now with the stock SA tables, and am just finding out that the VORTEC heads prefer a lower SA. Currently the Maximum SA scalar is set at 42 ( stock), Base timing and Spark Reference Angle Scalar is at 6 degrees, and the SA tables show MAX spark advance in the 48 range. Everything I can find on the net indicates that Max SA should be in the 30-32 range.

    Anyone had experience with this? Maybe someone has a BIN with a Spark Advance table already re-set that might give me a jump start? I assume that I need to reduce the Maximum SA scalar to something smaller, like 32?? And then re-set the SA Tables ( From 20 min as shown to say 32-34 in the highest regions, and then smooth out the curve? Any other table changes I should also consider?

    This is foreign territory for me, so any help would be appreciated.
    '85 SS El Camino, Gm Crate 350 L31, Vortec heads,TPI.
    https://sites.google.com/site/darbyselky/home

  2. #2
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    Quote Originally Posted by darbysan View Post
    I have a crate L31 ( Vortec Head 350) with TPI induction, running on ARAP bin with 1227165 ECM. I've been running for years now with the stock SA tables, and am just finding out that the VORTEC heads prefer a lower SA. Currently the Maximum SA scalar is set at 42 ( stock), Base timing and Spark Reference Angle Scalar is at 6 degrees, and the SA tables show MAX spark advance in the 48 range. Everything I can find on the net indicates that Max SA should be in the 30-32 range.

    Anyone had experience with this? Maybe someone has a BIN with a Spark Advance table already re-set that might give me a jump start? I assume that I need to reduce the Maximum SA scalar to something smaller, like 32?? And then re-set the SA Tables ( From 20 min as shown to say 32-34 in the highest regions, and then smooth out the curve? Any other table changes I should also consider?

    This is foreign territory for me, so any help would be appreciated.
    Max at WOT with Vortec heads should be in the 28-34* range. Part throttle can run as high as 46-52* at light throttle and light load. When my Express van still had cast iron vortecs I was in the 30-32* range at WOT and running 70 mph on flat road, about 50* @ 2,800 rpm and 50 kpa load.

    The GMPP distributor used on the 330 HP 350 Vortec.

    10* Initial Timing
    0* mechanical at 1,100 rpm
    12* mechanical at 1,600
    16* mechanical at 2,400 rpm
    22* mechanical at 4,600 rpm
    0* vacuum advance at 3"
    20* vacuum advance at 7.5"

    Add those values together and you get a maximum total advance of 52* BTDC under certain operating conditions.
    Last edited by Fast355; 1 Week Ago at 10:47 AM.

  3. #3
    Super Moderator dave w's Avatar
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    The link below is to a thread with an Excel spreadsheet showing a Stock 1998 L31 Vortec timing table.

    http://www.gearhead-efi.com/Fuel-Inj...c+timing+table

    dave w

  4. #4
    Fuel Injected! darbysan's Avatar
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    Thanks to all that replied. Looks like I need to go to work and just build something, as mine is a MAF system, so my tables differ. Guess I'll just go in and try pulling it down a ways and see what I get....

    I'm getting a resonant vibration around 2000 rpm, in all gears, so I'm curious to see if changing the timing in that range will help me in this regard. May be something else- I just keep peeling the onion
    '85 SS El Camino, Gm Crate 350 L31, Vortec heads,TPI.
    https://sites.google.com/site/darbyselky/home

  5. #5
    Super Moderator dave w's Avatar
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    Attached is a timing table from a 2002 Express Van, which uses MAF Grams / Cylinder vs. RPM. Only the Optimal and High Octane tables are in the spreadsheet.

    dave w
    Attached Files Attached Files

  6. #6
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    The LV8 value is far different than the 0411 tables. Truth of the matter is the Camaro/Firebird TPI timing values will not be far off what a Vortec TPI will want. You can try to re-invent the wheel but the OEM timing settings worked very well with only minor changes for me.

    My Express van loved more timing. The timing map programmed into the GM Ramjet 350 is very similar to what the GMPP HEI distributor runs above. My timing map in my Express as well as the one I use in other Vortecs is based off those.

    Before
    https://youtu.be/2CqkRkABKk4

    After
    https://youtu.be/yXTXqMCkF34
    Last edited by dave w; 6 Days Ago at 09:51 AM.

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