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Thread: 94 Firebird Formula speedo Scalar numbers needed for speed correction

  1. #1
    Carb and Points!
    Join Date
    Sep 2022

    94 Firebird Formula speedo Scalar numbers needed for speed correction

    Hi I have a '94 Firebird Formula LT1 and my Speedometer reads 3-4mph faster than my GPS speedometer App.
    I have 3.23 gears, 4L60E automatic transmission, 315/35ZR17 Nitto NT555 G-2 tires on 11" wide rims, tire height 25.67" 810 revs/mile
    Can anyone give me the speedometer Scalar numbers as I cannot open the speedometer calculator
    Speedo Scalar-Base
    Speedo Scalar-Divisor
    Speedo Scalar-Scan Tool
    Stopped vehicle VSS Pulse Delay
    I am using Tuner Pro to tune my car
    I would really appreciate the help
    thank you

  2. #2
    LT1 specialist steveo's Avatar
    Join Date
    Aug 2013
    just tweak your speedo scalar base a bit until the speed matches. the speedo spreadsheet will probably only get you within 1-2mph anyway

  3. #3
    Fuel Injected!
    Join Date
    Sep 2014
    OE values for 3.231 & 25.6" tall tires
    Base: 26
    Divisor: 1.0097
    ScanTool: 43.819
    VSS Pulse Delay: 34.26
    THEY are NOT Lying to You.
    You are NOT Even Lying to Yourself.
    You ARE Being Lied to ... by Your SELF.
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  4. #4
    Carb and Points!
    Join Date
    Sep 2022
    Thank you I will try adjusting the Scalar base

    And thanks for the OE values, I will start with that.

  5. #5
    Carb and Points!
    Join Date
    Sep 2022
    Hi I opened up my rear end and found out that I have 3.42 gears instead of 3.23 as stated before so can anyone help with the speedometer scalar numbers on a
    '94 Firebird Formula LT1
    4L60E automatic transmission,
    315/35ZR17 tires 25.67" 810 rev/mile,
    Speedo Scalar base-
    Speedo scalar-Divisor-
    Speedo scalar-scan tool-
    Stopped vehicle VSS pulse delay-40
    I would really appreciate the help
    I am using Tuner Pro
    Thank You

  6. #6
    Fuel Injected!
    Join Date
    Jul 2019
    Orange, CA
    Going by the math that's written in the XDF file itself, you'd want:

    Scalar Base: 27.702
    Scalar Divisor: 1
    Scantool: 46.17
    Driveshaft PPR: 40

    Now, to be fair, the math doesn't match GM calibrations. But since these are bases and divisors, multiple values can result in the same 'correct' answer. So try these values and see how it goes.
    1990 Corvette (Manual)
    1994 Corvette (Automatic)
    1995 Corvette (Manual)

  7. #7
    Carb and Points!
    Join Date
    Sep 2022
    Thank you, I appreciate your help. I did the math and got it wrong last time. I'm glad to say that I got what you got so I must have gotten it right this time.
    When I put these numbers in it rounded the Scalar Base up to 28 and it changed the Scalar divisor to .9999 in Tuner Pro. I will install my new tune and try it out.
    Thank You

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