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Thread: Timing for L31 Vortec

  1. #1
    Lifetime Member N0DIH's Avatar
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    Jan 2006

    Default Timing for L31 Vortec

    Has anyone experience in ignition timing the L31 350? I used to have a L31 350 in my old 96 Suburban. I have a 94 Cadillac Fleetwood with the LT1 with RPO V4P (aka, 7000# tow package). The heads on the iron LT1 are virtually identical to the L31 Vortec. My 3.42's and shorter tires have the same overall effective gear ratio as the truck does with its 3.73's. So, with the weight of my Fleetwood empty at 4400 lbs and the truck at 5200 lbs. Shouldn't the overall ignition timing be darn close to the same?

    So, when I look at the timing on my friend's 98 Suburban, it seems on average 10 degrees LOWER than my Cad. The Cad is a bullet compare to the Sub.

    Shouldn't they be much closer to each other in tuning? Both are intended for 87 octane with iron heads. The LT1 having around 0.5 to 1 point more compression.

    Or is this one of those cases where GM was just so pathetically conservative in the tune that the L31 just has a lot of power left untapped?

  2. #2
    Junior Member Danville Performance's Avatar
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    Jan 2006


    Yes GM likes to do funny stuff like that but there are a few more variables to look at also like load, areo drag, etc... The same timing curve from the car many cause a serious case of spark knock in the suburban. The more load put on the motor, the more heat that is generated, the more likely it is to spark knock. I am sure the fuel tables are also different between them and a few more tables.

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