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Thread: 4.56 gears in 07 denali

  1. #1
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    4.56 gears in 07 denali

    Ok, I am changing the gears in a 2007 4wd Yukon to 4.56 from 3.73's. In the speedo table, it is saying that it was 29.45" tires along with 4.10 gears stock (but they weren't - they were 3.73's). Should I just type in 4.56 and let it do an auto calculation? Will this come out correctly or should I do a manual conversion using a 1.22 (or a .8180- which is correct?) correction factor?

    Under final drive ratio, the trans is listed with 4.10 and the final is listed as 3.73. Do I have to increase both of these? Help, I am a little confused on this one.

    Mike

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    Ok, I reprogrammed it for the gears and new tires (32.5" tall) and the ABS and brake lights are on. The front wheel speed sensors are not reading the same as the rear. The fronts are reading about 18% less than the rear ones. I used all of the auto scale properites and the numbers do not make any sense on a couple of them. Acutally, the stock numbers make no sense, the new ones do, but apparently do not work!

    Can anyone help with this one?
    Last edited by Mike@ADS; 05-10-2007 at 09:01 PM. Reason: added base file

  3. #3
    Супер Модератор EC_Tune's Avatar
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    Need both files to see whats going on.
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    Here is the modded file as well. Notice that the ratio and ratio trans are totally different on the stock vehicle? It is strange because the truck had 3.73's, but HP says that it has 4.10 and 3.73's.

    Thanks,
    Mike

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    I have gone through and changed every number in the speedometer table and it does no good. The speedometer does change, but the difference from front to rear sensors will not change. It is always an 18% difference for some reason. The rear wheel speed sensors are taken from the tail shaft of the tranny and the fronts are actually on each hub. I don't have a wiring diagram for the 07's yet so I am not even sure where the wheel speed is going. It may be going through the ebcm first or something weird.

    Thanks,
    Mike

  6. #6
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    Further information needed on Speedo Discrepancies

    I am using HP Tuners VCM Suite Version 2.1.18.0

    The first screen capture is the stock speedo settings from the .hpt file posted above for the Yukon. The second is a capture from a stock 2006 LS2 SSR with an automatic transmission. (a file for a 2005 Automatic SSR is in the repository and it matches this as well).

    Both the Yukon (posted about above) and SSR have stock 3.73 differential gears.

    Can some one explain the fields in the attached .jpg Screen captures:
    1. Why are two different gear ratios used? One is 3.73 and the other is 4.10. If you do the hand calculations, The value in the Current Tire Size box was used with the 4.10 gear ratio and the 'VSS Tire Revs per Dist-Trans' value to get the 'VSS Pulses per mile' value. However, the tire size is wrong (too big). But, if you use the 3.73 gear ratio, 'VSS Tire Revs per Dist' and VSS Pulses to find the tire size, the tire size is just about exactly what you would expect.

    2. Why is the value (67.79 for Yukon and 70.21 for SSR) in 'VSS Tire Revs per Dist-Err' so much different than the value in 'VSS Tire Revs per Dist-T Err' (683.97 for Yukon and 709.7 for SSR)? Shouldn't these values match on each respective vehicle?

    3. Continuing with question 2. If I choose a ratio (any ratio) and Tire Size, and then apply the changes using the 'Commit' button, Why does HP Tuners insert the same value in Dist-Err and Dist- T Err boxes when they are so obviously different in stock files? Shouldn't the new values be proportional in all boxes????

    4. Using the formulae from another post on this bulletin board (Click Here), a tire size of 30.93 with 4.10 gears gives the following hand calculations:
    Tire Rev/Mile of 652.0567
    Trans Rev/Mile of 2673.4326
    VSS Pulses/Mile of 106937.30.

    Using the stock SSR file, HP Tuners gives:
    Tire Rev/Dist of 652.04
    VSS Tire Rev/Dist -Err of 652.06
    VSS Pulses per Mile of 104698 (or 104694 as read from PCM)

    What is the reason for the discrepancy between hand calculated values and the values in the HP Tuner fields when using the commit button? Nearly 2300 counts off in the ppm value is a significant error. This seems to be a software bug.

    There has been a consistent problem with updating the speedos in LS2 SSRs after gear changes. To my knowledge, no one has been successful in correctly setting an SSR speedo after changing from stock gears (3.73) to 4.56 when using HP Tuners. However, I understand there has been some success using HP Tuners after changing to 4.10. I suspect that 4.10 works because that is one of the settings in the stock file.

    Perhaps with insight into the reason for different ratios in the stock file we might figure out what is needed to make the 3.73 to 4.56 changes for both a Yukon and SSR??

    Anybody???
    Last edited by DBCKSSR; 09-03-2007 at 03:38 AM.

  7. #7
    Супер Модератор EC_Tune's Avatar
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    The front wheel sensor info is from the ABS system and is not changeable with HPT. Wish it was though...

    If you have an ABS light on you are going to have to play "fast & loose if you want the trans to shift correctly and not have ABS problems. The speedo should be calculated by the VSS Pulses per Mile value. That value can be calculated correctly using the roll out of the installed tires.

    Roll out Inches/Pi = Rolling tire diameter.
    Diameter * Final Drive * 40 (pulses per revolution) = VSS Pulses per Mile value
    Inches per mile (63360) / Roll out Inches = Tire Turns per Mile
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  8. #8
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    Quote Originally Posted by EC_Tune
    The speedo should be calculated by the VSS Pulses per Mile value. That value can be calculated correctly using the roll out of the installed tires.

    Roll out Inches/Pi = Rolling tire diameter.
    Diameter * Final Drive * 40 (pulses per revolution) = VSS Pulses per Mile value
    Inches per mile (63360) / Roll out Inches = Tire Turns per Mile
    Quote Originally Posted by DBCKSSR
    4. Using the formulae from another post on this bulletin board (CLICK HERE), a tire size of 30.93 with 4.10 gears gives the following hand calculations:
    Tire Rev/Mile of 652.0567
    Trans Rev/Mile of 2673.4326
    VSS Pulses/Mile of 106937.30.

    Using the stock SSR file, HP Tuners gives:
    Tire Rev/Dist of 652.04
    VSS Tire Rev/Dist -Err of 652.06
    VSS Pulses per Mile of 104698 (or 104694 as read from PCM)

    What is the reason for the discrepancy between hand calculated values and the values in the HP Tuner fields when using the commit button? Nearly 2300 counts off in the ppm value is a significant error. This seems to be a software bug.
    Those are good formulas and make perfect sense!! I even used them from one of your previous posts!! ... so I wonder why the values calculated using them do not match the values kicked out by HPT when you just enter the tire size and gear ratio and then hit commit? What is HPT doing different?

    And why the different gear ratios and inconsistent values in the different fields on the stock files?

  9. #9
    Супер Модератор EC_Tune's Avatar
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    That is a great question with no answer by me... Guess GM has 10,001 ways to calculate the speedo now...
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  10. #10
    Is your speedometer just reading incorrectly or freaking out? Where are you seeing the front wheel speed readings?

    I have a problem with my speedometer also... it pegs out by 8 mph (as indicated by gps) and then depending on the value entered in the VSS Pulses per Mile field it falls to 0 mph at speed. I am thinking I have a problem with the signal coming from my front wheel speed sensors as mentioned above.

  11. #11

    C6 Speedo Calc's

    This thing was really a challenge to dial in. I had to raise the failure rpms ffor the stall speed. Also did the auto scale, then put the tire height and gear ratio back to where it originally was. The car is a 2005 YB A4 with 2800 stall and 3.42 gears. BTW This car is a rocket with just these mods!

    I also did a 2007 YB A6 with 3.15 gears and used the same strategy other than the stall speed (It was still stock) and had no issues.
    Mark
    Mark